- Email: [email protected]
Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids
international journal of hydrogen energy xxx (xxxx) xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids S.Z. Hasan a,1,*, K.N. Ahmad a, W.N.R.W. Isahak a,b, M.S. Masdar a,b, J.M. Jahim a,b a
Research Centre for Sustainable Development Technology, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600, UKM, Bangi, Selangor, Malaysia b Chemical Engineering Programme, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600, UKM, Bangi, Selangor, Malaysia
highlights Synthesis of high surface energy NiO (111) using easy and one pot solid-state fusion method. The use of low-cost heterogeneous catalysts in CO2 hydrogenation. Significant amount of formic acid (8.13 mmol/L) and acetic acid (7.63 mmol/L) were produced.
article info
abstract
Article history:
Reducing gaseous carbon dioxide to valuable chemicals and fuels by using gaseous
Received 14 May 2019
hydrogen can decrease the concentration of greenhouse gases that contribute to global
Received in revised form
warming. Carbon dioxide conversion into fuels such as methane, methanol, and formic
19 August 2019
acid is a good hydrogen-storage method. In this paper, a comparative study of CO2 con-
Accepted 11 September 2019
version into formic and acetic acids on alumina-supported nickel oxide with and without
Available online xxx
the presence of carbon is reported. NiO (111) with high surface area was synthesized
Keywords:
thesized catalysts were tested in carbon dioxide hydrogenation reaction in a batch slurry
through a simple and one-pot fusion solid-state method at 550 C and 700 C. The synCO2 utilization
reactor at 130 C and under mild pressure. Interestingly, the optimum condition of the
Mitigation
reaction also successfully produced C2 carboxylic acid in significant amounts. The highest
NiO (111)
levels of formic acid and acetic acid production were 8.13 and 7.63 mmol/L, respectively.
Formic acid
© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
CeC bond
Introduction The prosperity era of energy-source production from fossil fuels such as coals, oils, and natural gases will inevitably end
because they are nonrenewable and not environment friendly. Fossil fuels produce CO2, a side product of combustion processes. Thus, other alternatives should be investigated to prevent the depletion of energy sources. Renewable energy sources, such as hydropower, modern biomass,
* Corresponding author. E-mail addresses: [email protected] (S.Z. Hasan), [email protected] (W.N.R.W. Isahak). 1 This paper is an extended and revised article presented at the International Conference on Sustainable Energy and Green Technology 2018 (SEGT 2018) on 11e14 December 2018 in Kuala Lumpur, Malaysia. https://doi.org/10.1016/j.ijhydene.2019.09.102 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
2
international journal of hydrogen energy xxx (xxxx) xxx
geothermal, solar, wind, and wave tide, should be considered alternatives to replace these nonrenewable energy sources [1,2]. To date, the use of hydrogen as an alternative energy source is a new promising way to replace energy sources from fossil fuels. The current investigation proves that only hydrogen acts as renewable energy carrier that can be prepared in real time and obtained efficiently without any material restriction [3,4]. To date, many researches reported various techniques and resources to produce hydrogen such as biological sources, wind, thermolysis, electrolysis, and photosplitting of water, reforming fossil fuels, metal hydrides compounds and chemical hydrides such as methane, methanol and formic acid [5,6]. Other than that, global warming also becomes an interesting topic nowadays since it has threatened the natural environment. It is known that the CO2 presence in the atmospheric space has caused global warming, and in 2016, approximately 94% of carbon dioxide emission was from fossil fuel consumption [7]. Global warming is a critical issue affecting the world to date. The increase in greenhouse gases from CO2 (65%) generally causes global warming [8]. At present, the CO2 concentration has increased up to 410 ppm in 2019, and from the last five years, the increment is approximately 3e4 ppm, as measured at Mauna Loa [9]. This phenomenon causes great concern because global warming leads to climate change, which in turn results in (1) tropical storms, (2) rise in sea level and coastal flooding, (3) El Nino, and La Nina that may affect rainfall and water supplies, (4) threats to inland plants and animals, and (5) worsened human health [10]. Therefore, reducing the atmospheric CO2 concentration must be mitigated. In order to mitigate CO2 concentration, technologies such as carbon capture and utilization have been developed [11e17]. CO2 conversion and utilization are two different terms with the same meaning used to mitigate CO2 in atmosphere space. The term CO2 conversion refers to CO2 transformation into chemically different forms that contain the CO2 carbon or that make use of its active “oxygen atom”. Meanwhile, CO2 utilization is the use of CO2 in both physical and chemical processes [18]. Compared with other methods (CO2 capture and CO2 storage), CO2 conversion and utilization reduce atmospheric CO2 concentration and convert CO2 into other valuable chemicals and fuels. CO2 is a simple molecule that consists of two oxygen atoms that are covalently bonded to one carbon atom. However, this molecule is thermodynamically very stable to be reduced to another valuable chemical. Therefore, the catalyst presence is very important because it can speed up the reaction rate by reducing the activation barrier for the reaction to proceed. Hydrogen is highly abundant, renewable fuel, clean, high energy density, safe and it was a most prominent fuel resources in the future [19e21]. Most of research into hydrogen storage is focused on storing hydrogen as a lightweight, liquid state and compact energy carrier for mobile applications [20], and this cause technology such as chemical hydride is needed. Currently, formic acid production from CO2 as the main feedstock has attracted scientists’ attention globally [22e25]. Formic acid production from CO2 reduces atmospheric CO2 concentration and stores H2 in liquid form, which is safe and nontoxic. In general, formic acid can be applied as a fuel in
direct formic acid fuel cells and can also be used as a potential chemical hydrogen storage material [26,27]. Therefore, the state-of-the-art of this study is to reduce CO2 into formic acid under a low-temperature reaction with the presence of the good activity of a low-cost catalyst. The use of highly active heterogeneous catalysts in the CO2 hydrogenation process is believed to convert CO2 into other valuable chemicals even at low temperature condition. Hence, tailoring the structure and properties of the catalyst with the simple synthesis method may achieve this objective. In order to reduce thermodynamically stable of CO2 molecule, highly potential modified transition metals may be use in the hydrogenation process. The use of noble metals as catalysts was applied many years ago. According to previous research, palladium (Pd), aurum (Au), and ruthenium (Ru) have been investigated in heterogeneous catalysts of CO2 hydrogenation into formate and formic acid products [28e34]. However, these catalysts are expensive and have limited availability, thus making them impractical to be used in catalytic hydrogenation from the industrial point of view. The use of non-noble metals is a good alternative in replacing noble metals because they exhibit both high activity and stability. Therefore, the aim of this work was to study the effect of NiO-based catalysts (with and without the presence of carbon) on CO2 hydrogenation reaction. The catalysts were prepared using a simple one-pot synthesis method namely fusion solidstate method. The catalysts were characterized using X-ray diffraction (XRD), BrunauereEmmetteTeller (BET) surface area, high-resolution field emission scanning electron microscopy (FESEM), Auger electron spectroscopy with X-ray photoelectron spectrometry (AES-XPS), and transmission electron microscopy (TEM). Moreover, the products from hydrogenation process were characterized using high performance liquid chromatography (HPLC) and gas chromatography (GC).
Experimental methods Catalyst synthesis and characterization NiOeC/Al2O3 catalysts were synthesized by fusion solid-state method where the precursors were mixed physically. Approximately 18.75 g of aluminum nitrate nonahydrate, 28.74 g citric acid, and 5.35 g nickel nitrate tetrahydrate were mixed together. After being well-mixed using a mortar, the catalyst samples were fused at 100 C in an oven and later calcined in air at 550 C and 700 C for 4 h [35]. The catalysts were labeled as NiOeC/Al2O3-550 and NiOeC/Al2O3-700 according to their calcination temperature. Another series of catalysts was synthesized using the same procedure with the citric acid absence. The catalysts were denoted as NiO/Al2O3550 and NiO/Al2O3-700. XRD was used to identify the phase structures of the catalysts (D8 Advanced, Bruker AXS Germany), with Cu Ka radiation in the range of 5 e80 at room temperature. Highresolution FESEM (Merlin Compact) was used to investigate the morphologies of the catalysts, and TEM analysis was performed on TEM Philips cm-12. A small quantity of the
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
international journal of hydrogen energy xxx (xxxx) xxx
catalysts was dispersed in ethanol and dried on the copper grids for the next measurement. For the specific surface area of the catalysts, Micromeritic ASAP 2020 with BET method was employed. The chemical state information of the element was investigated using AES-XPS (Axis Ultra DLD, Kratos/ Shimadzu).
Hydrogenation of CO2 CO2 was hydrogenated in a high-pressure stainless-steel autoclave reactor (250 mL; internal diameter, 60 mm) with a mechanical stirrer. In each experiment, 0.2 g of the catalyst was inserted into a batch reactor with 35 mL of 1,4-dioxane as a solvent. Prior to hydrogenation, the reactor was purged with H2 for 1 min. Then, the reactor was pressurized with 10 bar of CO2 and was filled up with H2 to the initial pressure of 35 bar. The system was heated to 130 C by a mantle fitted with a digital temperature controller. The reaction was conducted for a few hours. Next, the reactor was cooled down to room temperature naturally, and the gaseous sample was collected using a gasbag. Then, the remaining pressure was released to ambient condition. The liquid products obtained were filtered and analyzed with Agilent LC1100/1200 series high-performance liquid chromatography (HPLC) system with RP80 column (250 mm) at 30 C by using 0.1% H3PO4 as an eluent. The flow rate was maintained at 1 mL/min with a run time of 20 min and a UV detector of 210 nm. For gaseous products, the gas chromatography (GC) system from Agilent Technologies (6890 N) with thermal conductivity detector (TCD) was used to identify the gas composition from the reaction. Propack Q and molecular sieve column were used for the GC system. Fig. S1 shows the catalyst syntheses and CO2 hydrogenation.
Results and discussion Characterization of nano-NiO supported on Al2O3 Fig. 1(a) shows the XRD spectra for both NiOeC/Al2O3-550 and NiOeC/Al2O3-700 recorded in the range 5 e80 . The patterns were very different for both catalysts. However, they exhibited peak characteristics of NiO and g-Al2O3. NiOphase peaks were detected at 37.18 (311), 43.52 (200), 63.22 (220), and 75.83 (311). The NiO presence in NiOeC/Al2O3-550 was confirmed to be NiAl2O4 (PDF 01-078-6950). After calcination at 700 C, the diffraction pattern changed slightly with the no diffraction line at 63.22 and was confirmed with the database as NiAl2O4 (PDF 01-075-9711). Reportedly, composite containing NiAl2O4 phase may serve as a good catalyst in catalytic activity processes, such as steam reforming [36]. Moreover, the peaks for carbon were detected together at 19.74 , 31.75 , and 59.79 [37,38]. Carbon was generated from the citric acid addition as a gelling agent in the catalyst preparation. However, from the XRD diffraction line for NiOeC/Al2O3-550, the peak for carbon was not detected because of the structure formation of the catalyst as illustrated in Fig. 2(a). The illustration shows that the NiO nanoparticles had covered the Al2O3 surface and were connected with a carbon layer in between. Fig. 1(a) shows the
3
XRD spectra for samples obtained without using citric acid. The XRD pattern for both samples calcined at 550 C and 700 C were the same, and the peaks exhibited high intensity compared with the synthesized samples with the presence of citric acid. NiO-phase peaks were detected at 37.33 (111), 43.38 (200), 63.02 (220), and 75.59 (311) and were confirmed to be nickel oxide (PDF 01-073-1519). Compared with the catalyst synthesis by using citric acid, the NiO and Al2O3 peaks were separated, indicating slight NiAl2O4 formation. Fig. 2(b) shows the structure formation illustration of the catalysts. Fig. S2 displays the XRD spectra of the synthesized pure Al2O3 and NiO. The NiO spectrum shows all peaks exhibited high intensity, indicating the sample was in crystalline phase. In contrast to NiO, the peaks for Al2O3 were very broad, proving that the sample was in amorphous state. XRD results verified the carbon presence (from citric acid), causing strong interaction between the NiO particles and Al2O3 particle through the NiAl2O4 formation. The crystallite size of the samples can be calculated using the Scherrer's formula as shown in Equation (1) [39]. As shown in Fig. S3, the crystallite size for all samples varies. Al2O3 exhibited smaller crystallite size (11.27 nm) compared with NiO (26.85 nm). Combination of both NiO and Al2O3 via fusion solid-state method produced nanoparticles with crystallite size in the range of 7.19e24.61 nm. With increased temperature, the crystallite size of the catalyst increased from 7.19 nm (NiOeC/Al2O3-550) to 22.94 nm (NiOeC/Al2O3-700). Meanwhile, for NiO/Al2O3-550 and NiO/Al2O3-700, the crystallite size has changed from 22.39 nm to 24.61 nm. Moreover, the percentage crystallinity values recorded in the range of 5 e80 for NiOeC/Al2O3-550 and NiOeC/Al2O3-700 were found to be 53.4% and 43.1%, respectively. Increased temperature improves the crystallinity of Al2O3 [40]. However, this study obtained a contradicted result, and the decrease in crystallinity may be attributed to the exposed mesoporous carbon detected by the XRD analysis. Samples synthesized without the presence of citric acid showed a contrast result in terms of crystallinity percentage. With increased temperature from 550 C to 700 C, crystallinity also increased from 37.6% to 42.4% possibly because of the crystalline structure of Al2O3 and from XRD spectrum. Clearly, the intensity peaks for Al2O3 increased. Fig. 1(b) and S4 show the N2 adsorptionedesorption graphs and pore size distribution of all catalysts. All catalysts exhibited type IV physisorption isotherm where its hysteresis loops show the initial part attributed to the monolayer and multilayer adsorption [41]. As shown in Fig. S4, NiO and Al2O3 exhibited type H3 and H4 loops, respectively. Type H3 loop does not exhibit any limiting adsorption at high P/Po and is observed with the aggregates of plate-like particles [41]. However, the catalysts synthesized with and without citric acid showed the difference in hysteresis loops, wherein catalysts synthesized with the carbon presence exhibited type H2 loop that corresponded to the difference in mechanism between condensation and evaporation processes occurring in “ink-bottle” pores. Meanwhile, catalysts with the carbon absence exhibited type H4 loop often associated with narrow slit-like pores [41]. Table 1 and Table S3 show the physisorption measurement results for all synthesized catalysts. The crystalline NiO
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
4
international journal of hydrogen energy xxx (xxxx) xxx
Fig. 1 e (a) XRD spectra; (b) N2 adsorptionedesorption graphs of NiOeC/Al2O3 and NiO/Al2O3 and (c) XPS spectra (Ni 2p) of NiO/Al2O3 and NiOeC/Al2O3 calcined at 550 C.
Fig. 2 e Structure of (a) NiOeC/Al2O3 and (b) NiO/Al2O3 calcined at 550 C and 700 C. Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
international journal of hydrogen energy xxx (xxxx) xxx
Table 1 e BET surface area of NiO-supported Al2O3 calcined at 550 C and 700 C. Sample NiOeC/Al2O3550 NiOeC/Al2O3700 NiO/Al2O3550 NiO/Al2O3700
Surface area (m2/g)
Pore volume (cm3/g)
Pore size (nm)
160.2953
0.1465
3.9912
80.2440
0.0984
4.1746
195.4736
0.2045
3.8943
236.3036
0.1387
3.5266
exhibited the smallest surface area with 5.65 m2/g compared with Al2O3 (91.51 m2/g). However, by using Barrett, Joyner, and Halenda method for pore size measurement, NiO exhibited the largest pore size with 23.84 nm and the lowest pore volume (0.011 cm3/g). The NiOeC/Al2O3-550 exhibited a large specific surface area of 160.30 m2/g, pore volume (0.1465 cm3/ g), and small pore size with 3.99 nm. Meanwhile, NiOeC/ Al2O3-700 exhibited the smallest surface area (80.24 m2/g), pore volume (0.098 cm3/g), and the largest pore size with 4.18 nm. Results showed that the surface area of the catalyst decreased with increased temperature in catalyst with carbon. However, catalysts synthesized without citric acid showed larger surface area, pore volume, and smaller pore size compared with catalysts synthesized with citric acid. NiO/Al2O3-550 exhibited surface area (195.47 m2/g), pore volume (0.21 cm3/g), and pore size (3.9 nm). Moreover, with increased temperature, the surface area of the catalysts increased up to 236.30 m2/g but decreased in pore volume (0.14 cm3/g) and pore size of 3.53 nm (calcination temperature 700 C). The XPS catalysts were analyzed at the oxidized state, as shown in Fig. 1(c). From the obtained result, the binding energy values for Ni2p3/2 and Ni2p1/2 core level photoelectrons (NiOeC/Al2O3-550) were 854.41 and 871.6 eV, respectively, and satellite peaks were observed at 861.08 and 877.28 eV. Meanwhile, for NiO/Al2O3-550, the binding energy values for Ni2p3/2 and Ni2p1/2 core level photoelectrons were 855.11 and 872.6 eV, respectively. These results indicated that the nickel species in all samples were consists of Ni2þ. Figs. S5 and S6 show wide spectra of all elements occurring in the catalysts calcined at 550 C. All elements, such as Ni, Al, O, and C, are present in the samples. Even though catalyst synthesized with the carbon absence should not have C, a very low intensity peak of C is observed, corresponding to the adventitious carbon which usually found on the surface of most air exposed samples during calcination. dc ¼ kl=b cos q
(1)
where dc is the mean crystal size of catalyst particle (nm); k is the crystallite shape constant (0.94); l is the X-ray wavelength (0.15406 nm, Cu Ka); b is the full width at half maximum of peak, and q is the Bragg angle of peak. Fig. 3(a)e(d) and S7 show the FESEM images of the synthesized catalysts including NiO and Al2O3 samples. Under 50 000 magnification, the FESEM image of Al2O3 shows exhibited pores that contributed to the high surface area. In contrast to
5
Al2O3, NiO shows very agglomerated particles with nonuniform shape under the same magnification. The morphology of the samples started to change when both Al2O3 and NiO were synthesized together with and without the citric acid presence. In the sample synthesized with the presence of citric acid, NiOeC/Al2O3-550 exhibited a group of closely arranged spore-like morphology. In contrast to NiOeC/Al2O3550, NiOeC/Al2O3-700 exhibited the characteristic of a nonuniform rod-like morphology. As for samples synthesized with the absence of citric acid, nanoparticles clearly exhibited nearly uniform size for NiO/Al2O3-550. When the sample was calcined at 700 C, the nanoparticle shape became spherical and the nanoparticle size increased where particles compacting due to the sintering process. Results showed that the carbon presence and calcination temperature affected the morphologies of the products. Moreover, Fig. 3(e)e(h) shows the percentage of each element present in the catalysts where all catalysts contain the same amount of Ni (about 22%). To study the structure and size of synthesized catalysts under nanometer scale, TEM analysis was performed, as shown in Fig. 3(i)e(l). For NiOeC/Al2O3-550, the NiO nanoparticles were well-distributed on the support surface from small to large sizes. The sizes of NiO nanoparticles from NiOeC/Al2O3-550 and NiOeC/Al2O3-700 were in the range of 40e55 and 12e35 nm, respectively. As for samples synthesized with the absence of citric acid, the shape of the NiO nanoparticles with hexagonal shape can be clearly seen attached to the Al2O3 particles with the size of 35e40 nm. With increased calcination temperature, the NiO nanoparticle size and shape increased. Thus, the NiO nanoparticle size increased to 30e100 nm with increased temperature. Although TEM analysis showed increased NiO nanoparticle size, the crystallite size at (111) facet decreased from 17.5 nm to 12.7 nm (Fig. S3). Catalytic activity reportedly increases with decreased in nanoparticle size [42,43]. Thus, the combination between small nanoparticle size and high surface energy NiO (111) may increase the catalytic activity for CO2 hydrogenation. In contrast to NiO nanoparticles, the Al2O3 size became small for NiO/Al2O3-700. All the above results showed that increased temperature from 550 C to 700 C changed the morphology, size, crystallinity, and surface area of the catalyst.
Catalytic performance for CO2 hydrogenation to carboxylic acids The CO2 hydrogenation reaction was carried out in a batch reactor at 130 C for the evaluation of catalytic performance. The reactions were performed at different reaction times, from 2 h to 12 h for all catalysts. At the end of the reaction, liquid and gaseous products were analyzed using HPLC and a GC-TCD detector. Only liquid products were detected, and no gaseous products were detected except for CO2 and H2. With the presence of NiO supported on Al2O3 in 1,4-dioxane, CO2 was reduced to formic acid and acetic acid only in this study. The product yield was also calculated with an internal standard.
Effect of Al2O3 support Fig. S8 shows the results obtained from hydrogenation by using various catalysts. Formation of formic acid and acetic
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
6
international journal of hydrogen energy xxx (xxxx) xxx
Fig. 3 e SEM images of (a) NiOeC/Al2O3-550, (b) NiOeC/Al2O3-700, (c) NiO/Al2O3-550, (d) NiO/Al2O3-700; EDX spectra of (e) NiOeC/Al2O3-550, (f) NiOeC/Al2O3-700, (g) NiO/Al2O3-550, (h) NiO/Al2O3-700 and TEM images of (i) NiOeC/Al2O3-550, (j) NiOeC/Al2O3-700, (k) NiO/Al2O3-550 (l) NiO/Al2O3-700.
acid were low with the values of 0.24 and 0.73 mmol/L, respectively, when no catalysts are used at the same experimental condition (Fig. S8, Blank 1). When the experiment was run at room temperature (28 C) and with the presence of NiO/ Al2O3 (Fig. S8, Blank 2), the formation of the products was the lowest with the values of 0.05 mmol/L (formic acid) and 0.09 mmol/L (acetic acid). These results show the absence of catalyst and heat and the slow reaction rate in the formation of the products. With increased temperature, the energy increased and can be converted into activation energy in a collision that enhances the reaction rate. Al2O3 and NiO were tested separately to observe the effect of both support and catalyst during hydrogenation. Both support and catalyst
showed minimal formation of products with the values of formic acid and acetic acid of 0.59 and 0.51 mmol/L (Al2O3) and 0.39 and 1.68 mmol/L for NiO, respectively. However, when NiO nanoparticles were synthesized together with Al2O3 to produce Al2O3-supported NiO, the formation of products increased for all catalysts synthesized with and without the carbon presence. The synergistic effect between Al2O3 and NiO produced high concentration of carboxylic acids, whereas the use of only NiO or Al2O3 did not. It was reported in several researches that the presence of support in the catalyst system plays an important role by providing high surface area for an abundance clean active facets on the edge sites [25,44]. In this case, the exposed facet of NiO nanoparticles plays an
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
international journal of hydrogen energy xxx (xxxx) xxx
important role in catalytic activity. As mentioned previously, the NiO with (111) plane exhibited high surface energy, wherein charged planes produce a dipole moment perpendicular to the surface and thus can be associated with adsorption of foreign atoms, such as CO2 and H2 [45]. In catalysts synthesized with the presence of citric acid, the NiAl2O4 phase formation with high index surface (311) plane will own several step-edges and kinks for the adjacent surfaces of simple metals [46,47].
Effect of carbon on catalytic hydrogenation Fig. 4(a) and (b) show the product yield obtained from the CO2 hydrogenation by using catalysts synthesized with the carbon presence. For the NiOeC/Al2O3-550 catalyst, formic acid production increased from 2 h to 12 h, and the highest product concentration obtained was 0.61 mmol/L. However, this result was in contrast to that of acetic acid because prolonged time caused the acetic acid concentration to decrease from 0.04 mmol/L to 0 mmol/L. The product obtained for NiOeC/ Al2O3-700 was higher than that obtained for NiOeC/Al2O3-550. The optimum yield of formic acid obtained at 6 h was 4.08 mmo/L. However, the acetic acid yield was not comparable with formic acid because the obtained significant concentrations were 1.43 and 1.58 mmol/L at 6 and 10 h, respectively. The catalytic activity of NiOeC/Al2O3-700, which was better than that of NiOeC/Al2O3-550, was attributed to the catalyst structure and NiO size. As illustrated in Fig. 2(a), the rod-like structure provides a good catalytic activity because of NiO separation from carbon. Based on the result, when NiO completely linked together with carbon, the production of carboxylic acids was quite low. The interaction between NiO
7
with carbon might be the main reason for the low production of carboxylic acids because carbon is known to deactivate the catalyst and slows down the reaction rate [48]. Moreover, the small size of NiO nanoparticles provided a large active site that enhances the catalytic activity [49] and in this study, it enhances the CO2 and H2 adsorption on the nickel surface to produce several carboxylic acids. Although the surface area of NiOeC/Al2O3-700 was smaller than that of NiOeC/Al2O3-550, the production of carboxylic acids was high. This result proves that surface area is not the main factor affecting catalytic activity [50].
Effect of no carbon on catalytic hydrogenation Fig. 4(c) and (d) show the product formation from CO2 and H2 hydrogenation by using catalysts synthesized with the carbon absence. The results show that formation of products was higher when catalysts were synthesized with the carbon absence used during hydrogenation compared with the catalysts synthesized with the carbon presence. At 6 h reaction time, NiO/Al2O3-550 produced the highest concentration of formic acid and acetic acid with the values of 4.89 and 7.63 mmol/L, respectively, whereas NiO/Al2O3-700 produced 3.96 and 2.16 mmol/L formic acid and acetic acid, respectively. After 6 h reaction time, the product yield decreased and started to reach the dynamic equilibrium at 12 h reaction time. At 12 h reaction time, NiO/Al2O3-700 produced high yields of formic acid and acetic acid of 8.13 and 5 mmol/L, whereas NiO/ Al2O3-550 produced 1.72 mmol/L formic acid and 2.22 mmol/L acetic acid. A number of research were conducted to study the CO2 conversion into formic acid by using hydrothermal method
Fig. 4 e Formic acid and acetic acid yield as a function of NiO-based catalysts (a) NiOeC/Al2O3-550 (b), NiOeC/Al2O3-700 (c), NiO/Al2O3-550 (d) and NiO/Al2O3-700. Reaction conditions: 0.2 g of catalyst, 35 mL of 1,4-dioxane, pressure of 35 bar and temperature of 130 C. Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
8
international journal of hydrogen energy xxx (xxxx) xxx
(see Table 1). The results from this study were comparable with the results reported by others that used Ni and Cu-based catalysts in the studies [31,51e53]. However, when compared with noble metal catalysts, such as Ru on Al2O3 [32,33], the present study showed lower yield (Table 2). Currently, no established technologies are available that can transform CO2 from air into formic acid and use it directly in a fuel cell system. Researchers reported that in the future, to combine separate processes to produce an integrated system, which can utilize CO2 as the raw material to generate electricity by using a fuel cell system, is possible [54e56]. Therefore, the findings of this study can be used as additional knowledge for the production of formic acid from CO2 under low temperature and mild condition with the presence of a low-cost catalyst.
intermediate route, the formed intermediate combined with hydrogen to form formic acid and detached from the catalyst surface. As for acetic acid formation, the adsorbed CO2 on the surface of the catalysts will continue to react with H2 to form intermediate molecule (Fig. S10) and proceed for the further CeC bond formation in the presence of CO2 molecules. The CH bond activation of the adsorbed intermediate molecule by the aid of framework oxygen and surface organic species, formate, is the crucial step for the CeC bond generation from C1 formic acid. Acetic acid was desorbed from the surface of the catalyst, leaving the hydroxyl group (OH) on the NiO/Al2O3 surface to form NiO(OH)2/Al2O3.
Plausible mechanism of the reaction for formic acid and acetic acid formation
Nano-nickel (II) oxide-supported alumina catalysts were successfully synthesized at 550 C and 700 C by using the fusion solid-state method with and without the presence of citric acid. A comparative investigation of the carbon dioxide conversion into formic acid and acetic acid on alumina-supported nickel oxide with and without the presence of carbon is reported. The XRD results showed the presence of nickel (II) oxide with (111) facet, spinel nickel aluminate (311) facet, and alumina mixture in the samples. Moreover, only nickel (II) species was detected for nickel element. Samples synthesized with the presence of citric acid showed the carbon which influence in the morphology formation that affected the formation of formic acid and acetic acid. However, it does not exceed the yield of the catalysts without carbon content. With increased temperature, the morphology, size, crystallinity, and surface area changed. The temperature calcination played an important role in carbon dioxide hydrogenation. Nickel (II) oxides supported on alumina calcined at 700 C presented a good activity for carbon dioxide hydrogenation to carboxylic acids at mild condition pressure and low temperature of 35 bar and 130 C, respectively. Nickel (II) oxide supported on alumina calcined at 700 C exhibiting a rod-like morphology and small crystallite size of nickel (II) oxide nanoparticles (12.7 nm) at (111) facet produced the highest formic acid and acetic acid with values of 8.13 and 5.00 mmol/L, respectively.
Eqs. (2) and (3) show the stoichiometric equations for the formation of formic acid and acetic acid from CO2 and H2 reaction by using NiO/Al2O3. CO2 ðgÞ þ H2 ðgÞ/ HCOOH; ðlÞ NiO=Al2 O3
(2)
2CO2 ðgÞ þ 3H2 ðgÞ/H3 CCOOH ðlÞ þ NiOðOHÞ2 Al2 O3 ðsÞ NiO=Al2 O3 (3) The theoretical study on the reaction pathways for the formation of formic acid and acetic acid from CO2 hydrogenation via heterogeneous catalysts has been reported [57e60]. The study on density functional theory (about electronic structure methods) can be semi-quantitatively used for surface treatment processes on transition-metal surfaces to investigate the reaction pathway [61]. In this study, direct CO2 hydrogenation into formic acid and acetic acid can be performed via formate intermediates. Hydrogen and carbon dioxide were adsorbed on the NiO/Al2O3 surface, and CO2 was adsorbed in the form of formate intermediate. Herein, a possible reaction mechanism for formic acid production was proposed, as illustrated in Fig. S9. From the formate-
Conclusion
Table 2 e Comparison of hydrogenation of CO2 into formic acid and acetic acid.
Acknowledgements
Catalyst
This work was supported by Ministry of Higher Education (MOHE) Malaysia (FRGS/1/2015/SG01/UKM/02/2, DIP-2016-010, DIP-2018-021); Universiti Kebangsaan Malaysia for the scholarship (Zamalah scheme) and instruments (Centre of Research & Innovation Management and Electron Microscope Unit).
NiO/Al2O3-550 NiO/Al2O3-700 NiOeC/Al2O3-550 NiOeC/Al2O3-700 Fe NiFe Cu/ZnO/Al2O3 PdNi/CNT-GR Ru/Al2O3 Ru/Al2O3-n
Yield of products (mmol) HCOOH
CH3COOH
4.89 8.13 0.61 4.08 1.9 0.06 0.41 1.92 9.1 13.1
7.63 5.00 0 1.43 2.4 No formation No formation No formation No formation No formation
Ref.
This This This This [53] [51] [52] [31] [32] [33]
study study study study
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.ijhydene.2019.09.102.
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
international journal of hydrogen energy xxx (xxxx) xxx
references
[1] Franzitta V, Curto D, Milone D, Rao D. Assessment of renewable sources for the energy consumption in Malta in the Mediterranean Sea. Energies 2016;9:1034. [2] Abe J, Ajenifuja E, Popoola O. Hydrogen energy, economy and storage: review and recommendation. Int J Hydrogen Energy 2019;44:15072e86. [3] Andreas Zu¨ttel AB, Schlapbach Louis. Hydrogen as a future energy carrier: book review. Environ Eng Manag J 2008;7:343e4. [4] Teichmann D, Arlt W, Wasserscheid P. Liquid Organic Hydrogen Carriers as an efficient vector for the transport and storage of renewable energy. Int J Hydrogen Energy 2012;37:18118e32. [5] Niaz S, Manzoor T, Pandith AH. Hydrogen storage: materials, methods and perspectives. Renew Sustain Energy Rev 2015;50:457e69. [6] Baykara SZ. Hydrogen: a brief overview on its sources, production and environmental impact. Int J Hydrogen Energy 2018;43:10605e14. [7] Administration EI. Greenhouse gas emissions and atmospheric concentrations have increased over the past 150 years. 2018. . [Accessed 28 February 2019]. [8] United States Environmental Protection Agency. Greenhouse gas emissions. https://wwwepagov/ghgemissions/overviewgreenhouse-gases. [Accessed 1 May 2017]. [9] Earth System Research Laboratory, Trends in atmospheric carbon dioxide. http://wwwesrlnoaagov/gmd/ccgg/trends/ 2018 (accessed 26.11.2018). [10] Hansen J, Kharecha P, Sato M, Masson-Delmotte V, Ackerman F, Beerling DJ, et al. Assessing “dangerous climate change”: required reduction of carbon emissions to protect young people, future generations and nature. PLoS One 2013;8:e81648. n M, Vega F, Alonso[11] Baena-Moreno FM, Rodrı´guez-Gala ~ as B, Vilches Arenas LF, Navarrete B. Carbon capture Farin and utilization technologies: a literature review and recent advances. Energy Sources, Part A Recovery, Util Environ Eff 2019;41:1403e33. [12] Bui M, Adjiman CS, Bardow A, Anthony EJ, Boston A, Brown S, et al. Carbon capture and storage (CCS): the way forward. Energy Environ Sci 2018;11:1062e176. [13] Nahar S, Zain M, Kadhum AAH, Hasan HA, Hasan MR. Advances in photocatalytic CO2 reduction with water: a review. Materials 2017;10:629. [14] Wan Isahak WNR, Che Ramli ZA, Mohamed Hisham MW, Yarmo MA. The formation of a series of carbonates from carbon dioxide: capturing and utilisation. Renew Sustain Energy Rev 2015;47:93e106. [15] Abdullah H, Khan MMR, Ong HR, Yaakob Z. Modified TiO2 photocatalyst for CO2 photocatalytic reduction: an overview. J CO2 Util 2017;22:15e32. [16] Abdullah H, Khan MR, Pudukudy M, Yaakob Z, Ismail NA. CeO2-TiO2 as a visible light active catalyst for the photoreduction of CO2 to methanol. J Rare Earths 2015;33:1155e61. [17] Hakim A, Marliza TS, Abu Tahari NM, Wan Isahak RW, Yusop RM, Mohamed Hisham WM, et al. Studies on CO2 adsorption and desorption properties from various types of iron oxides (FeO, Fe2O3, and Fe3O4). Ind Eng Chem Res 2016;55:7888e97. [18] Song C. CO2 conversion and utilization: an overview. ACS Symp Ser 2002;809:2e30. [19] Veziro T, Barbir F. Hydrogen: the wonder fuel. Int J Hydrogen Energy 1992;17:391e404.
9
€ nkvist S. Large-scale storage of hydrogen. [20] Andersson J, Gro Int J Hydrogen Energy 2019;44:11901e19. [21] Kojima Y. Hydrogen storage materials for hydrogen and energy carriers. Int J Hydrogen Energy 2019;44:18179e92. [22] Gunasekar GH, Park K, Jung K-D, Yoon S. Recent developments in the catalytic hydrogenation of CO2 to formic acid/formate using heterogeneous catalysts. Inorgan Chem Front 2016;3:882e95. rez-Fortes M, Scho € neberger JC, Boulamanti A, Harrison G, [23] Pe Tzimas E. Formic acid synthesis using CO2 as raw material: techno-economic and environmental evaluation and market potential. Int J Hydrogen Energy 2016;41:16444e62. [24] Yao G, Zeng X, Jin Y, Zhong H, Duo J, Jin F. Hydrogen production by water splitting with Al and in-situ reduction of CO2 into formic acid. Int J Hydrogen Energy 2015;40:14284e9. [25] Liu K-H, Zhong H-X, Li S-J, Duan Y-X, Shi M-M, Zhang X-B, et al. Advanced catalysts for sustainable hydrogen generation and storage via hydrogen evolution and carbon dioxide/nitrogen reduction reactions. Prog Mater Sci 2018;92:64e111. [26] Singh AK, Singh S, Kumar A. Hydrogen energy future with formic acid: a renewable chemical hydrogen storage system. Catal Sci Technol 2016;6:12e40. [27] Rice C, Ha S, Masel R, Waszczuk P, Wieckowski A, Barnard T. Direct formic acid fuel cells. J Power Sources 2002;111:83e9. [28] Stalder CJ, Chao S, Summers DP, Wrighton MS. Supported palladium catalysts for the reduction of sodium bicarbonate to sodium formate in aqueous solution at room temperature and one atmosphere of hydrogen. J Am Chem Soc 1983;105:6318e20. [29] Preti D, Resta C, Squarcialupi S, Fachinetti G. Carbon dioxide hydrogenation to formic acid by using a heterogeneous gold catalyst. Angew Chem Int Ed 2011;50:12551e4. [30] Su J, Lu M, Lin H. High yield production of formate by hydrogenating CO2 derived ammonium carbamate/ carbonate at room temperature. Green Chem 2015;17:2769e73. [31] Nguyen LTM, Park H, Banu M, Kim JY, Youn DH, Magesh G, et al. Catalytic CO2 hydrogenation to formic acid over carbon nanotube-graphene supported PdNi alloy catalysts. RSC Adv 2015;5:105560e6. [32] Hao C, Wang S, Li M, Kang L, Ma X. Hydrogenation of CO2 to formic acid on supported ruthenium catalysts. Catal Today 2011;160:184e90. [33] Liu N, Du RJ, Li W. Hydrogenation CO2 to formic acid over Ru supported on g-Al2O3 nanorods. Adv Mater Res 2013;821:1330e5. [34] Filonenko GA, Vrijburg WL, Hensen EJ, Pidko EA. On the activity of supported Au catalysts in the liquid phase hydrogenation of CO2 to formates. J Catal 2016;343:97e105. [35] Pudukudy M, Yaakob Z, Takriff MS. Methane decomposition into COx free hydrogen and multiwalled carbon nanotubes over ceria, zirconia and lanthana supported nickel catalysts prepared via a facile solid state citrate fusion method. Energy Convers Manag 2016;126:302e15. [36] Nathan TJ, Pottebaum AJ, Uz V, Laine RM. The bottom up approach is not always the best processing method: dense aAl2O3/NiAl2O4 composites. Adv Funct Mater 2014;24:3392e408. [37] Rajan AS, Sampath S, Shukla AK. An in situ carbon-grafted alkaline iron electrode for iron-based accumulators. Energy Environ Sci 2014;7:1110e6. [38] Inagaki M, Okada Y, Miura H, Konno H. Preparation of carbon-coated transition metal particles from mixtures of metal oxide and polyvinylchloride. Carbon 1999;37:329e34. [39] Varghese T, Balakrishna K. Nanotechnology: an introduction to synthesis, properties and applications. New Delhi: Atlantic Publishers; 2011.
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
10
international journal of hydrogen energy xxx (xxxx) xxx
[40] Sun Z-X, Zheng T-T, Bo Q-B, Du M, Forsling W. Effects of calcination temperature on the pore size and wall crystalline structure of mesoporous alumina. J Colloid Interface Sci 2008;319:247e51. [41] Sing KS. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984). Pure Appl Chem 1985;57:603e19. [42] Farin D, Kiwi J, Avnir D. Size effects in photoprocesses on dispersed catalysts. J Phys Chem 1989;93:5851e4. ski A, Bonarowska M. Relation between crystallite [43] Borodzin size and dispersion on supported metal catalysts. Langmuir 1997;13:5613e20. [44] Zhong H-X, Zhang Q, Wang J, Zhang X-B, Wei X-L, Wu Z-J, et al. Engineering ultrathin C3N4 quantum dots on graphene as a metal-free water reduction electrocatalyst. ACS Catal 2018;8:3965e70. [45] Tasker PW. The stability of ionic crystal surfaces. J Phys C Solid State Phys 1979;12:4977e84. [46] Sun W, Ceder G. A topological screening heuristic for lowenergy, high-index surfaces. Surf Sci 2018;669:50e6. [47] Bao D, Zhang Q, Meng FL, Zhong HX, Shi MM, Zhang Y, et al. Electrochemical reduction of N2 under ambient conditions for artificial N2 fixation and renewable energy storage using N2/NH3 cycle. Adv Mater 2017;29:1604799. [48] Huang C, Chen S, Fei X, Liu D, Zhang Y. Catalytic hydrogenation of CO2 to methanol: study of synergistic effect on adsorption properties of CO2 and H2 in CuO/ZnO/ZrO2 system. Catalysts 2015;5:1846e61. [49] Jung Y-S, Yoon W-L, Seo Y-S, Rhee Y-W. The effect of precipitants on Ni-Al2O3 catalysts prepared by a coprecipitation method for internal reforming in molten carbonate fuel cells. Catal Commun 2012;26:103e11. [50] Kobayashi Y, Horiguchi J, Kobayashi S, Yamazaki Y, Omata K, Nagao D, et al. Effect of NiO content in mesoporous
[51]
[52]
[53]
[54]
[55] [56] [57]
[58]
[59]
[60]
[61]
NiOeAl2O3 catalysts for high pressure partial oxidation of methane to syngas. Appl Catal Gen 2011;395:129e37. Takahashi H, Liu L, Yashiro Y, Ioku K, Bignall G, Yamasaki N, et al. CO2 reduction using hydrothermal method for the selective formation of organic compounds. J Mater Sci 2006;41:1585e9. Chiang C-L, Lin K-S, Chuang H-W. Direct synthesis of formic acid via CO2 hydrogenation over Cu/ZnO/Al2O3 catalyst. J Clean Prod 2018;172:1957e77. He C, Tian G, Liu Z, Feng S. A mild hydrothermal route to fix carbon dioxide to simple carboxylic acids. Org Lett 2010;12:649e51. Jeong K-J, Miesse CM, Choi J-H, Lee J, Han J, Yoon SP, et al. Fuel crossover in direct formic acid fuel cells. J Power Sources 2007;168:119e25. Cano-Castillo U. Hydrogen and fuel cells: potential elements in the energy transition scenario. Rev Mex Fis 2013;59:85e92. McKeown C, Rhen FM. Pt-Au film catalyst for formic acid oxidation. Procedia Eng 2017;215:211e8. Peng G, Sibener S, Schatz GC, Ceyer ST, Mavrikakis M. CO2 hydrogenation to formic acid on Ni (111). J Phys Chem C 2012;116:3001e6. Peng G, Sibener S, Schatz GC, Mavrikakis M. CO2 hydrogenation to formic acid on Ni (110). Surf Sci 2012;606:1050e5. Vesselli E, Rizzi M, De Rogatis L, Ding X, Baraldi A, Comelli G, et al. Hydrogen-assisted transformation of CO2 on nickel: the role of formate and carbon monoxide. J Phys Chem Lett 2009;1:402e6. Sirijaraensre J, Limtrakul J. Hydrogenation of CO2 to formic acid over a Cu-embedded graphene: a DFT study. Appl Surf Sci 2016;364:241e8. Wang J-G, Liu C-J, Zhang Y-P, Eliasson B. A DFT study of synthesis of acetic acid from methane and carbon dioxide. Chem Phys Lett 2003;368:313e8.
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids S.Z. Hasan a,1,*, K.N. Ahmad a, W.N.R.W. Isahak a,b, M.S. Masdar a,b, J.M. Jahim a,b a
Research Centre for Sustainable Development Technology, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600, UKM, Bangi, Selangor, Malaysia b Chemical Engineering Programme, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600, UKM, Bangi, Selangor, Malaysia
highlights Synthesis of high surface energy NiO (111) using easy and one pot solid-state fusion method. The use of low-cost heterogeneous catalysts in CO2 hydrogenation. Significant amount of formic acid (8.13 mmol/L) and acetic acid (7.63 mmol/L) were produced.
article info
abstract
Article history:
Reducing gaseous carbon dioxide to valuable chemicals and fuels by using gaseous
Received 14 May 2019
hydrogen can decrease the concentration of greenhouse gases that contribute to global
Received in revised form
warming. Carbon dioxide conversion into fuels such as methane, methanol, and formic
19 August 2019
acid is a good hydrogen-storage method. In this paper, a comparative study of CO2 con-
Accepted 11 September 2019
version into formic and acetic acids on alumina-supported nickel oxide with and without
Available online xxx
the presence of carbon is reported. NiO (111) with high surface area was synthesized
Keywords:
thesized catalysts were tested in carbon dioxide hydrogenation reaction in a batch slurry
through a simple and one-pot fusion solid-state method at 550 C and 700 C. The synCO2 utilization
reactor at 130 C and under mild pressure. Interestingly, the optimum condition of the
Mitigation
reaction also successfully produced C2 carboxylic acid in significant amounts. The highest
NiO (111)
levels of formic acid and acetic acid production were 8.13 and 7.63 mmol/L, respectively.
Formic acid
© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
CeC bond
Introduction The prosperity era of energy-source production from fossil fuels such as coals, oils, and natural gases will inevitably end
because they are nonrenewable and not environment friendly. Fossil fuels produce CO2, a side product of combustion processes. Thus, other alternatives should be investigated to prevent the depletion of energy sources. Renewable energy sources, such as hydropower, modern biomass,
* Corresponding author. E-mail addresses: [email protected] (S.Z. Hasan), [email protected] (W.N.R.W. Isahak). 1 This paper is an extended and revised article presented at the International Conference on Sustainable Energy and Green Technology 2018 (SEGT 2018) on 11e14 December 2018 in Kuala Lumpur, Malaysia. https://doi.org/10.1016/j.ijhydene.2019.09.102 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
2
international journal of hydrogen energy xxx (xxxx) xxx
geothermal, solar, wind, and wave tide, should be considered alternatives to replace these nonrenewable energy sources [1,2]. To date, the use of hydrogen as an alternative energy source is a new promising way to replace energy sources from fossil fuels. The current investigation proves that only hydrogen acts as renewable energy carrier that can be prepared in real time and obtained efficiently without any material restriction [3,4]. To date, many researches reported various techniques and resources to produce hydrogen such as biological sources, wind, thermolysis, electrolysis, and photosplitting of water, reforming fossil fuels, metal hydrides compounds and chemical hydrides such as methane, methanol and formic acid [5,6]. Other than that, global warming also becomes an interesting topic nowadays since it has threatened the natural environment. It is known that the CO2 presence in the atmospheric space has caused global warming, and in 2016, approximately 94% of carbon dioxide emission was from fossil fuel consumption [7]. Global warming is a critical issue affecting the world to date. The increase in greenhouse gases from CO2 (65%) generally causes global warming [8]. At present, the CO2 concentration has increased up to 410 ppm in 2019, and from the last five years, the increment is approximately 3e4 ppm, as measured at Mauna Loa [9]. This phenomenon causes great concern because global warming leads to climate change, which in turn results in (1) tropical storms, (2) rise in sea level and coastal flooding, (3) El Nino, and La Nina that may affect rainfall and water supplies, (4) threats to inland plants and animals, and (5) worsened human health [10]. Therefore, reducing the atmospheric CO2 concentration must be mitigated. In order to mitigate CO2 concentration, technologies such as carbon capture and utilization have been developed [11e17]. CO2 conversion and utilization are two different terms with the same meaning used to mitigate CO2 in atmosphere space. The term CO2 conversion refers to CO2 transformation into chemically different forms that contain the CO2 carbon or that make use of its active “oxygen atom”. Meanwhile, CO2 utilization is the use of CO2 in both physical and chemical processes [18]. Compared with other methods (CO2 capture and CO2 storage), CO2 conversion and utilization reduce atmospheric CO2 concentration and convert CO2 into other valuable chemicals and fuels. CO2 is a simple molecule that consists of two oxygen atoms that are covalently bonded to one carbon atom. However, this molecule is thermodynamically very stable to be reduced to another valuable chemical. Therefore, the catalyst presence is very important because it can speed up the reaction rate by reducing the activation barrier for the reaction to proceed. Hydrogen is highly abundant, renewable fuel, clean, high energy density, safe and it was a most prominent fuel resources in the future [19e21]. Most of research into hydrogen storage is focused on storing hydrogen as a lightweight, liquid state and compact energy carrier for mobile applications [20], and this cause technology such as chemical hydride is needed. Currently, formic acid production from CO2 as the main feedstock has attracted scientists’ attention globally [22e25]. Formic acid production from CO2 reduces atmospheric CO2 concentration and stores H2 in liquid form, which is safe and nontoxic. In general, formic acid can be applied as a fuel in
direct formic acid fuel cells and can also be used as a potential chemical hydrogen storage material [26,27]. Therefore, the state-of-the-art of this study is to reduce CO2 into formic acid under a low-temperature reaction with the presence of the good activity of a low-cost catalyst. The use of highly active heterogeneous catalysts in the CO2 hydrogenation process is believed to convert CO2 into other valuable chemicals even at low temperature condition. Hence, tailoring the structure and properties of the catalyst with the simple synthesis method may achieve this objective. In order to reduce thermodynamically stable of CO2 molecule, highly potential modified transition metals may be use in the hydrogenation process. The use of noble metals as catalysts was applied many years ago. According to previous research, palladium (Pd), aurum (Au), and ruthenium (Ru) have been investigated in heterogeneous catalysts of CO2 hydrogenation into formate and formic acid products [28e34]. However, these catalysts are expensive and have limited availability, thus making them impractical to be used in catalytic hydrogenation from the industrial point of view. The use of non-noble metals is a good alternative in replacing noble metals because they exhibit both high activity and stability. Therefore, the aim of this work was to study the effect of NiO-based catalysts (with and without the presence of carbon) on CO2 hydrogenation reaction. The catalysts were prepared using a simple one-pot synthesis method namely fusion solidstate method. The catalysts were characterized using X-ray diffraction (XRD), BrunauereEmmetteTeller (BET) surface area, high-resolution field emission scanning electron microscopy (FESEM), Auger electron spectroscopy with X-ray photoelectron spectrometry (AES-XPS), and transmission electron microscopy (TEM). Moreover, the products from hydrogenation process were characterized using high performance liquid chromatography (HPLC) and gas chromatography (GC).
Experimental methods Catalyst synthesis and characterization NiOeC/Al2O3 catalysts were synthesized by fusion solid-state method where the precursors were mixed physically. Approximately 18.75 g of aluminum nitrate nonahydrate, 28.74 g citric acid, and 5.35 g nickel nitrate tetrahydrate were mixed together. After being well-mixed using a mortar, the catalyst samples were fused at 100 C in an oven and later calcined in air at 550 C and 700 C for 4 h [35]. The catalysts were labeled as NiOeC/Al2O3-550 and NiOeC/Al2O3-700 according to their calcination temperature. Another series of catalysts was synthesized using the same procedure with the citric acid absence. The catalysts were denoted as NiO/Al2O3550 and NiO/Al2O3-700. XRD was used to identify the phase structures of the catalysts (D8 Advanced, Bruker AXS Germany), with Cu Ka radiation in the range of 5 e80 at room temperature. Highresolution FESEM (Merlin Compact) was used to investigate the morphologies of the catalysts, and TEM analysis was performed on TEM Philips cm-12. A small quantity of the
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
international journal of hydrogen energy xxx (xxxx) xxx
catalysts was dispersed in ethanol and dried on the copper grids for the next measurement. For the specific surface area of the catalysts, Micromeritic ASAP 2020 with BET method was employed. The chemical state information of the element was investigated using AES-XPS (Axis Ultra DLD, Kratos/ Shimadzu).
Hydrogenation of CO2 CO2 was hydrogenated in a high-pressure stainless-steel autoclave reactor (250 mL; internal diameter, 60 mm) with a mechanical stirrer. In each experiment, 0.2 g of the catalyst was inserted into a batch reactor with 35 mL of 1,4-dioxane as a solvent. Prior to hydrogenation, the reactor was purged with H2 for 1 min. Then, the reactor was pressurized with 10 bar of CO2 and was filled up with H2 to the initial pressure of 35 bar. The system was heated to 130 C by a mantle fitted with a digital temperature controller. The reaction was conducted for a few hours. Next, the reactor was cooled down to room temperature naturally, and the gaseous sample was collected using a gasbag. Then, the remaining pressure was released to ambient condition. The liquid products obtained were filtered and analyzed with Agilent LC1100/1200 series high-performance liquid chromatography (HPLC) system with RP80 column (250 mm) at 30 C by using 0.1% H3PO4 as an eluent. The flow rate was maintained at 1 mL/min with a run time of 20 min and a UV detector of 210 nm. For gaseous products, the gas chromatography (GC) system from Agilent Technologies (6890 N) with thermal conductivity detector (TCD) was used to identify the gas composition from the reaction. Propack Q and molecular sieve column were used for the GC system. Fig. S1 shows the catalyst syntheses and CO2 hydrogenation.
Results and discussion Characterization of nano-NiO supported on Al2O3 Fig. 1(a) shows the XRD spectra for both NiOeC/Al2O3-550 and NiOeC/Al2O3-700 recorded in the range 5 e80 . The patterns were very different for both catalysts. However, they exhibited peak characteristics of NiO and g-Al2O3. NiOphase peaks were detected at 37.18 (311), 43.52 (200), 63.22 (220), and 75.83 (311). The NiO presence in NiOeC/Al2O3-550 was confirmed to be NiAl2O4 (PDF 01-078-6950). After calcination at 700 C, the diffraction pattern changed slightly with the no diffraction line at 63.22 and was confirmed with the database as NiAl2O4 (PDF 01-075-9711). Reportedly, composite containing NiAl2O4 phase may serve as a good catalyst in catalytic activity processes, such as steam reforming [36]. Moreover, the peaks for carbon were detected together at 19.74 , 31.75 , and 59.79 [37,38]. Carbon was generated from the citric acid addition as a gelling agent in the catalyst preparation. However, from the XRD diffraction line for NiOeC/Al2O3-550, the peak for carbon was not detected because of the structure formation of the catalyst as illustrated in Fig. 2(a). The illustration shows that the NiO nanoparticles had covered the Al2O3 surface and were connected with a carbon layer in between. Fig. 1(a) shows the
3
XRD spectra for samples obtained without using citric acid. The XRD pattern for both samples calcined at 550 C and 700 C were the same, and the peaks exhibited high intensity compared with the synthesized samples with the presence of citric acid. NiO-phase peaks were detected at 37.33 (111), 43.38 (200), 63.02 (220), and 75.59 (311) and were confirmed to be nickel oxide (PDF 01-073-1519). Compared with the catalyst synthesis by using citric acid, the NiO and Al2O3 peaks were separated, indicating slight NiAl2O4 formation. Fig. 2(b) shows the structure formation illustration of the catalysts. Fig. S2 displays the XRD spectra of the synthesized pure Al2O3 and NiO. The NiO spectrum shows all peaks exhibited high intensity, indicating the sample was in crystalline phase. In contrast to NiO, the peaks for Al2O3 were very broad, proving that the sample was in amorphous state. XRD results verified the carbon presence (from citric acid), causing strong interaction between the NiO particles and Al2O3 particle through the NiAl2O4 formation. The crystallite size of the samples can be calculated using the Scherrer's formula as shown in Equation (1) [39]. As shown in Fig. S3, the crystallite size for all samples varies. Al2O3 exhibited smaller crystallite size (11.27 nm) compared with NiO (26.85 nm). Combination of both NiO and Al2O3 via fusion solid-state method produced nanoparticles with crystallite size in the range of 7.19e24.61 nm. With increased temperature, the crystallite size of the catalyst increased from 7.19 nm (NiOeC/Al2O3-550) to 22.94 nm (NiOeC/Al2O3-700). Meanwhile, for NiO/Al2O3-550 and NiO/Al2O3-700, the crystallite size has changed from 22.39 nm to 24.61 nm. Moreover, the percentage crystallinity values recorded in the range of 5 e80 for NiOeC/Al2O3-550 and NiOeC/Al2O3-700 were found to be 53.4% and 43.1%, respectively. Increased temperature improves the crystallinity of Al2O3 [40]. However, this study obtained a contradicted result, and the decrease in crystallinity may be attributed to the exposed mesoporous carbon detected by the XRD analysis. Samples synthesized without the presence of citric acid showed a contrast result in terms of crystallinity percentage. With increased temperature from 550 C to 700 C, crystallinity also increased from 37.6% to 42.4% possibly because of the crystalline structure of Al2O3 and from XRD spectrum. Clearly, the intensity peaks for Al2O3 increased. Fig. 1(b) and S4 show the N2 adsorptionedesorption graphs and pore size distribution of all catalysts. All catalysts exhibited type IV physisorption isotherm where its hysteresis loops show the initial part attributed to the monolayer and multilayer adsorption [41]. As shown in Fig. S4, NiO and Al2O3 exhibited type H3 and H4 loops, respectively. Type H3 loop does not exhibit any limiting adsorption at high P/Po and is observed with the aggregates of plate-like particles [41]. However, the catalysts synthesized with and without citric acid showed the difference in hysteresis loops, wherein catalysts synthesized with the carbon presence exhibited type H2 loop that corresponded to the difference in mechanism between condensation and evaporation processes occurring in “ink-bottle” pores. Meanwhile, catalysts with the carbon absence exhibited type H4 loop often associated with narrow slit-like pores [41]. Table 1 and Table S3 show the physisorption measurement results for all synthesized catalysts. The crystalline NiO
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
4
international journal of hydrogen energy xxx (xxxx) xxx
Fig. 1 e (a) XRD spectra; (b) N2 adsorptionedesorption graphs of NiOeC/Al2O3 and NiO/Al2O3 and (c) XPS spectra (Ni 2p) of NiO/Al2O3 and NiOeC/Al2O3 calcined at 550 C.
Fig. 2 e Structure of (a) NiOeC/Al2O3 and (b) NiO/Al2O3 calcined at 550 C and 700 C. Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
international journal of hydrogen energy xxx (xxxx) xxx
Table 1 e BET surface area of NiO-supported Al2O3 calcined at 550 C and 700 C. Sample NiOeC/Al2O3550 NiOeC/Al2O3700 NiO/Al2O3550 NiO/Al2O3700
Surface area (m2/g)
Pore volume (cm3/g)
Pore size (nm)
160.2953
0.1465
3.9912
80.2440
0.0984
4.1746
195.4736
0.2045
3.8943
236.3036
0.1387
3.5266
exhibited the smallest surface area with 5.65 m2/g compared with Al2O3 (91.51 m2/g). However, by using Barrett, Joyner, and Halenda method for pore size measurement, NiO exhibited the largest pore size with 23.84 nm and the lowest pore volume (0.011 cm3/g). The NiOeC/Al2O3-550 exhibited a large specific surface area of 160.30 m2/g, pore volume (0.1465 cm3/ g), and small pore size with 3.99 nm. Meanwhile, NiOeC/ Al2O3-700 exhibited the smallest surface area (80.24 m2/g), pore volume (0.098 cm3/g), and the largest pore size with 4.18 nm. Results showed that the surface area of the catalyst decreased with increased temperature in catalyst with carbon. However, catalysts synthesized without citric acid showed larger surface area, pore volume, and smaller pore size compared with catalysts synthesized with citric acid. NiO/Al2O3-550 exhibited surface area (195.47 m2/g), pore volume (0.21 cm3/g), and pore size (3.9 nm). Moreover, with increased temperature, the surface area of the catalysts increased up to 236.30 m2/g but decreased in pore volume (0.14 cm3/g) and pore size of 3.53 nm (calcination temperature 700 C). The XPS catalysts were analyzed at the oxidized state, as shown in Fig. 1(c). From the obtained result, the binding energy values for Ni2p3/2 and Ni2p1/2 core level photoelectrons (NiOeC/Al2O3-550) were 854.41 and 871.6 eV, respectively, and satellite peaks were observed at 861.08 and 877.28 eV. Meanwhile, for NiO/Al2O3-550, the binding energy values for Ni2p3/2 and Ni2p1/2 core level photoelectrons were 855.11 and 872.6 eV, respectively. These results indicated that the nickel species in all samples were consists of Ni2þ. Figs. S5 and S6 show wide spectra of all elements occurring in the catalysts calcined at 550 C. All elements, such as Ni, Al, O, and C, are present in the samples. Even though catalyst synthesized with the carbon absence should not have C, a very low intensity peak of C is observed, corresponding to the adventitious carbon which usually found on the surface of most air exposed samples during calcination. dc ¼ kl=b cos q
(1)
where dc is the mean crystal size of catalyst particle (nm); k is the crystallite shape constant (0.94); l is the X-ray wavelength (0.15406 nm, Cu Ka); b is the full width at half maximum of peak, and q is the Bragg angle of peak. Fig. 3(a)e(d) and S7 show the FESEM images of the synthesized catalysts including NiO and Al2O3 samples. Under 50 000 magnification, the FESEM image of Al2O3 shows exhibited pores that contributed to the high surface area. In contrast to
5
Al2O3, NiO shows very agglomerated particles with nonuniform shape under the same magnification. The morphology of the samples started to change when both Al2O3 and NiO were synthesized together with and without the citric acid presence. In the sample synthesized with the presence of citric acid, NiOeC/Al2O3-550 exhibited a group of closely arranged spore-like morphology. In contrast to NiOeC/Al2O3550, NiOeC/Al2O3-700 exhibited the characteristic of a nonuniform rod-like morphology. As for samples synthesized with the absence of citric acid, nanoparticles clearly exhibited nearly uniform size for NiO/Al2O3-550. When the sample was calcined at 700 C, the nanoparticle shape became spherical and the nanoparticle size increased where particles compacting due to the sintering process. Results showed that the carbon presence and calcination temperature affected the morphologies of the products. Moreover, Fig. 3(e)e(h) shows the percentage of each element present in the catalysts where all catalysts contain the same amount of Ni (about 22%). To study the structure and size of synthesized catalysts under nanometer scale, TEM analysis was performed, as shown in Fig. 3(i)e(l). For NiOeC/Al2O3-550, the NiO nanoparticles were well-distributed on the support surface from small to large sizes. The sizes of NiO nanoparticles from NiOeC/Al2O3-550 and NiOeC/Al2O3-700 were in the range of 40e55 and 12e35 nm, respectively. As for samples synthesized with the absence of citric acid, the shape of the NiO nanoparticles with hexagonal shape can be clearly seen attached to the Al2O3 particles with the size of 35e40 nm. With increased calcination temperature, the NiO nanoparticle size and shape increased. Thus, the NiO nanoparticle size increased to 30e100 nm with increased temperature. Although TEM analysis showed increased NiO nanoparticle size, the crystallite size at (111) facet decreased from 17.5 nm to 12.7 nm (Fig. S3). Catalytic activity reportedly increases with decreased in nanoparticle size [42,43]. Thus, the combination between small nanoparticle size and high surface energy NiO (111) may increase the catalytic activity for CO2 hydrogenation. In contrast to NiO nanoparticles, the Al2O3 size became small for NiO/Al2O3-700. All the above results showed that increased temperature from 550 C to 700 C changed the morphology, size, crystallinity, and surface area of the catalyst.
Catalytic performance for CO2 hydrogenation to carboxylic acids The CO2 hydrogenation reaction was carried out in a batch reactor at 130 C for the evaluation of catalytic performance. The reactions were performed at different reaction times, from 2 h to 12 h for all catalysts. At the end of the reaction, liquid and gaseous products were analyzed using HPLC and a GC-TCD detector. Only liquid products were detected, and no gaseous products were detected except for CO2 and H2. With the presence of NiO supported on Al2O3 in 1,4-dioxane, CO2 was reduced to formic acid and acetic acid only in this study. The product yield was also calculated with an internal standard.
Effect of Al2O3 support Fig. S8 shows the results obtained from hydrogenation by using various catalysts. Formation of formic acid and acetic
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
6
international journal of hydrogen energy xxx (xxxx) xxx
Fig. 3 e SEM images of (a) NiOeC/Al2O3-550, (b) NiOeC/Al2O3-700, (c) NiO/Al2O3-550, (d) NiO/Al2O3-700; EDX spectra of (e) NiOeC/Al2O3-550, (f) NiOeC/Al2O3-700, (g) NiO/Al2O3-550, (h) NiO/Al2O3-700 and TEM images of (i) NiOeC/Al2O3-550, (j) NiOeC/Al2O3-700, (k) NiO/Al2O3-550 (l) NiO/Al2O3-700.
acid were low with the values of 0.24 and 0.73 mmol/L, respectively, when no catalysts are used at the same experimental condition (Fig. S8, Blank 1). When the experiment was run at room temperature (28 C) and with the presence of NiO/ Al2O3 (Fig. S8, Blank 2), the formation of the products was the lowest with the values of 0.05 mmol/L (formic acid) and 0.09 mmol/L (acetic acid). These results show the absence of catalyst and heat and the slow reaction rate in the formation of the products. With increased temperature, the energy increased and can be converted into activation energy in a collision that enhances the reaction rate. Al2O3 and NiO were tested separately to observe the effect of both support and catalyst during hydrogenation. Both support and catalyst
showed minimal formation of products with the values of formic acid and acetic acid of 0.59 and 0.51 mmol/L (Al2O3) and 0.39 and 1.68 mmol/L for NiO, respectively. However, when NiO nanoparticles were synthesized together with Al2O3 to produce Al2O3-supported NiO, the formation of products increased for all catalysts synthesized with and without the carbon presence. The synergistic effect between Al2O3 and NiO produced high concentration of carboxylic acids, whereas the use of only NiO or Al2O3 did not. It was reported in several researches that the presence of support in the catalyst system plays an important role by providing high surface area for an abundance clean active facets on the edge sites [25,44]. In this case, the exposed facet of NiO nanoparticles plays an
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
international journal of hydrogen energy xxx (xxxx) xxx
important role in catalytic activity. As mentioned previously, the NiO with (111) plane exhibited high surface energy, wherein charged planes produce a dipole moment perpendicular to the surface and thus can be associated with adsorption of foreign atoms, such as CO2 and H2 [45]. In catalysts synthesized with the presence of citric acid, the NiAl2O4 phase formation with high index surface (311) plane will own several step-edges and kinks for the adjacent surfaces of simple metals [46,47].
Effect of carbon on catalytic hydrogenation Fig. 4(a) and (b) show the product yield obtained from the CO2 hydrogenation by using catalysts synthesized with the carbon presence. For the NiOeC/Al2O3-550 catalyst, formic acid production increased from 2 h to 12 h, and the highest product concentration obtained was 0.61 mmol/L. However, this result was in contrast to that of acetic acid because prolonged time caused the acetic acid concentration to decrease from 0.04 mmol/L to 0 mmol/L. The product obtained for NiOeC/ Al2O3-700 was higher than that obtained for NiOeC/Al2O3-550. The optimum yield of formic acid obtained at 6 h was 4.08 mmo/L. However, the acetic acid yield was not comparable with formic acid because the obtained significant concentrations were 1.43 and 1.58 mmol/L at 6 and 10 h, respectively. The catalytic activity of NiOeC/Al2O3-700, which was better than that of NiOeC/Al2O3-550, was attributed to the catalyst structure and NiO size. As illustrated in Fig. 2(a), the rod-like structure provides a good catalytic activity because of NiO separation from carbon. Based on the result, when NiO completely linked together with carbon, the production of carboxylic acids was quite low. The interaction between NiO
7
with carbon might be the main reason for the low production of carboxylic acids because carbon is known to deactivate the catalyst and slows down the reaction rate [48]. Moreover, the small size of NiO nanoparticles provided a large active site that enhances the catalytic activity [49] and in this study, it enhances the CO2 and H2 adsorption on the nickel surface to produce several carboxylic acids. Although the surface area of NiOeC/Al2O3-700 was smaller than that of NiOeC/Al2O3-550, the production of carboxylic acids was high. This result proves that surface area is not the main factor affecting catalytic activity [50].
Effect of no carbon on catalytic hydrogenation Fig. 4(c) and (d) show the product formation from CO2 and H2 hydrogenation by using catalysts synthesized with the carbon absence. The results show that formation of products was higher when catalysts were synthesized with the carbon absence used during hydrogenation compared with the catalysts synthesized with the carbon presence. At 6 h reaction time, NiO/Al2O3-550 produced the highest concentration of formic acid and acetic acid with the values of 4.89 and 7.63 mmol/L, respectively, whereas NiO/Al2O3-700 produced 3.96 and 2.16 mmol/L formic acid and acetic acid, respectively. After 6 h reaction time, the product yield decreased and started to reach the dynamic equilibrium at 12 h reaction time. At 12 h reaction time, NiO/Al2O3-700 produced high yields of formic acid and acetic acid of 8.13 and 5 mmol/L, whereas NiO/ Al2O3-550 produced 1.72 mmol/L formic acid and 2.22 mmol/L acetic acid. A number of research were conducted to study the CO2 conversion into formic acid by using hydrothermal method
Fig. 4 e Formic acid and acetic acid yield as a function of NiO-based catalysts (a) NiOeC/Al2O3-550 (b), NiOeC/Al2O3-700 (c), NiO/Al2O3-550 (d) and NiO/Al2O3-700. Reaction conditions: 0.2 g of catalyst, 35 mL of 1,4-dioxane, pressure of 35 bar and temperature of 130 C. Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
8
international journal of hydrogen energy xxx (xxxx) xxx
(see Table 1). The results from this study were comparable with the results reported by others that used Ni and Cu-based catalysts in the studies [31,51e53]. However, when compared with noble metal catalysts, such as Ru on Al2O3 [32,33], the present study showed lower yield (Table 2). Currently, no established technologies are available that can transform CO2 from air into formic acid and use it directly in a fuel cell system. Researchers reported that in the future, to combine separate processes to produce an integrated system, which can utilize CO2 as the raw material to generate electricity by using a fuel cell system, is possible [54e56]. Therefore, the findings of this study can be used as additional knowledge for the production of formic acid from CO2 under low temperature and mild condition with the presence of a low-cost catalyst.
intermediate route, the formed intermediate combined with hydrogen to form formic acid and detached from the catalyst surface. As for acetic acid formation, the adsorbed CO2 on the surface of the catalysts will continue to react with H2 to form intermediate molecule (Fig. S10) and proceed for the further CeC bond formation in the presence of CO2 molecules. The CH bond activation of the adsorbed intermediate molecule by the aid of framework oxygen and surface organic species, formate, is the crucial step for the CeC bond generation from C1 formic acid. Acetic acid was desorbed from the surface of the catalyst, leaving the hydroxyl group (OH) on the NiO/Al2O3 surface to form NiO(OH)2/Al2O3.
Plausible mechanism of the reaction for formic acid and acetic acid formation
Nano-nickel (II) oxide-supported alumina catalysts were successfully synthesized at 550 C and 700 C by using the fusion solid-state method with and without the presence of citric acid. A comparative investigation of the carbon dioxide conversion into formic acid and acetic acid on alumina-supported nickel oxide with and without the presence of carbon is reported. The XRD results showed the presence of nickel (II) oxide with (111) facet, spinel nickel aluminate (311) facet, and alumina mixture in the samples. Moreover, only nickel (II) species was detected for nickel element. Samples synthesized with the presence of citric acid showed the carbon which influence in the morphology formation that affected the formation of formic acid and acetic acid. However, it does not exceed the yield of the catalysts without carbon content. With increased temperature, the morphology, size, crystallinity, and surface area changed. The temperature calcination played an important role in carbon dioxide hydrogenation. Nickel (II) oxides supported on alumina calcined at 700 C presented a good activity for carbon dioxide hydrogenation to carboxylic acids at mild condition pressure and low temperature of 35 bar and 130 C, respectively. Nickel (II) oxide supported on alumina calcined at 700 C exhibiting a rod-like morphology and small crystallite size of nickel (II) oxide nanoparticles (12.7 nm) at (111) facet produced the highest formic acid and acetic acid with values of 8.13 and 5.00 mmol/L, respectively.
Eqs. (2) and (3) show the stoichiometric equations for the formation of formic acid and acetic acid from CO2 and H2 reaction by using NiO/Al2O3. CO2 ðgÞ þ H2 ðgÞ/ HCOOH; ðlÞ NiO=Al2 O3
(2)
2CO2 ðgÞ þ 3H2 ðgÞ/H3 CCOOH ðlÞ þ NiOðOHÞ2 Al2 O3 ðsÞ NiO=Al2 O3 (3) The theoretical study on the reaction pathways for the formation of formic acid and acetic acid from CO2 hydrogenation via heterogeneous catalysts has been reported [57e60]. The study on density functional theory (about electronic structure methods) can be semi-quantitatively used for surface treatment processes on transition-metal surfaces to investigate the reaction pathway [61]. In this study, direct CO2 hydrogenation into formic acid and acetic acid can be performed via formate intermediates. Hydrogen and carbon dioxide were adsorbed on the NiO/Al2O3 surface, and CO2 was adsorbed in the form of formate intermediate. Herein, a possible reaction mechanism for formic acid production was proposed, as illustrated in Fig. S9. From the formate-
Conclusion
Table 2 e Comparison of hydrogenation of CO2 into formic acid and acetic acid.
Acknowledgements
Catalyst
This work was supported by Ministry of Higher Education (MOHE) Malaysia (FRGS/1/2015/SG01/UKM/02/2, DIP-2016-010, DIP-2018-021); Universiti Kebangsaan Malaysia for the scholarship (Zamalah scheme) and instruments (Centre of Research & Innovation Management and Electron Microscope Unit).
NiO/Al2O3-550 NiO/Al2O3-700 NiOeC/Al2O3-550 NiOeC/Al2O3-700 Fe NiFe Cu/ZnO/Al2O3 PdNi/CNT-GR Ru/Al2O3 Ru/Al2O3-n
Yield of products (mmol) HCOOH
CH3COOH
4.89 8.13 0.61 4.08 1.9 0.06 0.41 1.92 9.1 13.1
7.63 5.00 0 1.43 2.4 No formation No formation No formation No formation No formation
Ref.
This This This This [53] [51] [52] [31] [32] [33]
study study study study
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.ijhydene.2019.09.102.
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
international journal of hydrogen energy xxx (xxxx) xxx
references
[1] Franzitta V, Curto D, Milone D, Rao D. Assessment of renewable sources for the energy consumption in Malta in the Mediterranean Sea. Energies 2016;9:1034. [2] Abe J, Ajenifuja E, Popoola O. Hydrogen energy, economy and storage: review and recommendation. Int J Hydrogen Energy 2019;44:15072e86. [3] Andreas Zu¨ttel AB, Schlapbach Louis. Hydrogen as a future energy carrier: book review. Environ Eng Manag J 2008;7:343e4. [4] Teichmann D, Arlt W, Wasserscheid P. Liquid Organic Hydrogen Carriers as an efficient vector for the transport and storage of renewable energy. Int J Hydrogen Energy 2012;37:18118e32. [5] Niaz S, Manzoor T, Pandith AH. Hydrogen storage: materials, methods and perspectives. Renew Sustain Energy Rev 2015;50:457e69. [6] Baykara SZ. Hydrogen: a brief overview on its sources, production and environmental impact. Int J Hydrogen Energy 2018;43:10605e14. [7] Administration EI. Greenhouse gas emissions and atmospheric concentrations have increased over the past 150 years. 2018. . [Accessed 28 February 2019]. [8] United States Environmental Protection Agency. Greenhouse gas emissions. https://wwwepagov/ghgemissions/overviewgreenhouse-gases. [Accessed 1 May 2017]. [9] Earth System Research Laboratory, Trends in atmospheric carbon dioxide. http://wwwesrlnoaagov/gmd/ccgg/trends/ 2018 (accessed 26.11.2018). [10] Hansen J, Kharecha P, Sato M, Masson-Delmotte V, Ackerman F, Beerling DJ, et al. Assessing “dangerous climate change”: required reduction of carbon emissions to protect young people, future generations and nature. PLoS One 2013;8:e81648. n M, Vega F, Alonso[11] Baena-Moreno FM, Rodrı´guez-Gala ~ as B, Vilches Arenas LF, Navarrete B. Carbon capture Farin and utilization technologies: a literature review and recent advances. Energy Sources, Part A Recovery, Util Environ Eff 2019;41:1403e33. [12] Bui M, Adjiman CS, Bardow A, Anthony EJ, Boston A, Brown S, et al. Carbon capture and storage (CCS): the way forward. Energy Environ Sci 2018;11:1062e176. [13] Nahar S, Zain M, Kadhum AAH, Hasan HA, Hasan MR. Advances in photocatalytic CO2 reduction with water: a review. Materials 2017;10:629. [14] Wan Isahak WNR, Che Ramli ZA, Mohamed Hisham MW, Yarmo MA. The formation of a series of carbonates from carbon dioxide: capturing and utilisation. Renew Sustain Energy Rev 2015;47:93e106. [15] Abdullah H, Khan MMR, Ong HR, Yaakob Z. Modified TiO2 photocatalyst for CO2 photocatalytic reduction: an overview. J CO2 Util 2017;22:15e32. [16] Abdullah H, Khan MR, Pudukudy M, Yaakob Z, Ismail NA. CeO2-TiO2 as a visible light active catalyst for the photoreduction of CO2 to methanol. J Rare Earths 2015;33:1155e61. [17] Hakim A, Marliza TS, Abu Tahari NM, Wan Isahak RW, Yusop RM, Mohamed Hisham WM, et al. Studies on CO2 adsorption and desorption properties from various types of iron oxides (FeO, Fe2O3, and Fe3O4). Ind Eng Chem Res 2016;55:7888e97. [18] Song C. CO2 conversion and utilization: an overview. ACS Symp Ser 2002;809:2e30. [19] Veziro T, Barbir F. Hydrogen: the wonder fuel. Int J Hydrogen Energy 1992;17:391e404.
9
€ nkvist S. Large-scale storage of hydrogen. [20] Andersson J, Gro Int J Hydrogen Energy 2019;44:11901e19. [21] Kojima Y. Hydrogen storage materials for hydrogen and energy carriers. Int J Hydrogen Energy 2019;44:18179e92. [22] Gunasekar GH, Park K, Jung K-D, Yoon S. Recent developments in the catalytic hydrogenation of CO2 to formic acid/formate using heterogeneous catalysts. Inorgan Chem Front 2016;3:882e95. rez-Fortes M, Scho € neberger JC, Boulamanti A, Harrison G, [23] Pe Tzimas E. Formic acid synthesis using CO2 as raw material: techno-economic and environmental evaluation and market potential. Int J Hydrogen Energy 2016;41:16444e62. [24] Yao G, Zeng X, Jin Y, Zhong H, Duo J, Jin F. Hydrogen production by water splitting with Al and in-situ reduction of CO2 into formic acid. Int J Hydrogen Energy 2015;40:14284e9. [25] Liu K-H, Zhong H-X, Li S-J, Duan Y-X, Shi M-M, Zhang X-B, et al. Advanced catalysts for sustainable hydrogen generation and storage via hydrogen evolution and carbon dioxide/nitrogen reduction reactions. Prog Mater Sci 2018;92:64e111. [26] Singh AK, Singh S, Kumar A. Hydrogen energy future with formic acid: a renewable chemical hydrogen storage system. Catal Sci Technol 2016;6:12e40. [27] Rice C, Ha S, Masel R, Waszczuk P, Wieckowski A, Barnard T. Direct formic acid fuel cells. J Power Sources 2002;111:83e9. [28] Stalder CJ, Chao S, Summers DP, Wrighton MS. Supported palladium catalysts for the reduction of sodium bicarbonate to sodium formate in aqueous solution at room temperature and one atmosphere of hydrogen. J Am Chem Soc 1983;105:6318e20. [29] Preti D, Resta C, Squarcialupi S, Fachinetti G. Carbon dioxide hydrogenation to formic acid by using a heterogeneous gold catalyst. Angew Chem Int Ed 2011;50:12551e4. [30] Su J, Lu M, Lin H. High yield production of formate by hydrogenating CO2 derived ammonium carbamate/ carbonate at room temperature. Green Chem 2015;17:2769e73. [31] Nguyen LTM, Park H, Banu M, Kim JY, Youn DH, Magesh G, et al. Catalytic CO2 hydrogenation to formic acid over carbon nanotube-graphene supported PdNi alloy catalysts. RSC Adv 2015;5:105560e6. [32] Hao C, Wang S, Li M, Kang L, Ma X. Hydrogenation of CO2 to formic acid on supported ruthenium catalysts. Catal Today 2011;160:184e90. [33] Liu N, Du RJ, Li W. Hydrogenation CO2 to formic acid over Ru supported on g-Al2O3 nanorods. Adv Mater Res 2013;821:1330e5. [34] Filonenko GA, Vrijburg WL, Hensen EJ, Pidko EA. On the activity of supported Au catalysts in the liquid phase hydrogenation of CO2 to formates. J Catal 2016;343:97e105. [35] Pudukudy M, Yaakob Z, Takriff MS. Methane decomposition into COx free hydrogen and multiwalled carbon nanotubes over ceria, zirconia and lanthana supported nickel catalysts prepared via a facile solid state citrate fusion method. Energy Convers Manag 2016;126:302e15. [36] Nathan TJ, Pottebaum AJ, Uz V, Laine RM. The bottom up approach is not always the best processing method: dense aAl2O3/NiAl2O4 composites. Adv Funct Mater 2014;24:3392e408. [37] Rajan AS, Sampath S, Shukla AK. An in situ carbon-grafted alkaline iron electrode for iron-based accumulators. Energy Environ Sci 2014;7:1110e6. [38] Inagaki M, Okada Y, Miura H, Konno H. Preparation of carbon-coated transition metal particles from mixtures of metal oxide and polyvinylchloride. Carbon 1999;37:329e34. [39] Varghese T, Balakrishna K. Nanotechnology: an introduction to synthesis, properties and applications. New Delhi: Atlantic Publishers; 2011.
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102
10
international journal of hydrogen energy xxx (xxxx) xxx
[40] Sun Z-X, Zheng T-T, Bo Q-B, Du M, Forsling W. Effects of calcination temperature on the pore size and wall crystalline structure of mesoporous alumina. J Colloid Interface Sci 2008;319:247e51. [41] Sing KS. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984). Pure Appl Chem 1985;57:603e19. [42] Farin D, Kiwi J, Avnir D. Size effects in photoprocesses on dispersed catalysts. J Phys Chem 1989;93:5851e4. ski A, Bonarowska M. Relation between crystallite [43] Borodzin size and dispersion on supported metal catalysts. Langmuir 1997;13:5613e20. [44] Zhong H-X, Zhang Q, Wang J, Zhang X-B, Wei X-L, Wu Z-J, et al. Engineering ultrathin C3N4 quantum dots on graphene as a metal-free water reduction electrocatalyst. ACS Catal 2018;8:3965e70. [45] Tasker PW. The stability of ionic crystal surfaces. J Phys C Solid State Phys 1979;12:4977e84. [46] Sun W, Ceder G. A topological screening heuristic for lowenergy, high-index surfaces. Surf Sci 2018;669:50e6. [47] Bao D, Zhang Q, Meng FL, Zhong HX, Shi MM, Zhang Y, et al. Electrochemical reduction of N2 under ambient conditions for artificial N2 fixation and renewable energy storage using N2/NH3 cycle. Adv Mater 2017;29:1604799. [48] Huang C, Chen S, Fei X, Liu D, Zhang Y. Catalytic hydrogenation of CO2 to methanol: study of synergistic effect on adsorption properties of CO2 and H2 in CuO/ZnO/ZrO2 system. Catalysts 2015;5:1846e61. [49] Jung Y-S, Yoon W-L, Seo Y-S, Rhee Y-W. The effect of precipitants on Ni-Al2O3 catalysts prepared by a coprecipitation method for internal reforming in molten carbonate fuel cells. Catal Commun 2012;26:103e11. [50] Kobayashi Y, Horiguchi J, Kobayashi S, Yamazaki Y, Omata K, Nagao D, et al. Effect of NiO content in mesoporous
[51]
[52]
[53]
[54]
[55] [56] [57]
[58]
[59]
[60]
[61]
NiOeAl2O3 catalysts for high pressure partial oxidation of methane to syngas. Appl Catal Gen 2011;395:129e37. Takahashi H, Liu L, Yashiro Y, Ioku K, Bignall G, Yamasaki N, et al. CO2 reduction using hydrothermal method for the selective formation of organic compounds. J Mater Sci 2006;41:1585e9. Chiang C-L, Lin K-S, Chuang H-W. Direct synthesis of formic acid via CO2 hydrogenation over Cu/ZnO/Al2O3 catalyst. J Clean Prod 2018;172:1957e77. He C, Tian G, Liu Z, Feng S. A mild hydrothermal route to fix carbon dioxide to simple carboxylic acids. Org Lett 2010;12:649e51. Jeong K-J, Miesse CM, Choi J-H, Lee J, Han J, Yoon SP, et al. Fuel crossover in direct formic acid fuel cells. J Power Sources 2007;168:119e25. Cano-Castillo U. Hydrogen and fuel cells: potential elements in the energy transition scenario. Rev Mex Fis 2013;59:85e92. McKeown C, Rhen FM. Pt-Au film catalyst for formic acid oxidation. Procedia Eng 2017;215:211e8. Peng G, Sibener S, Schatz GC, Ceyer ST, Mavrikakis M. CO2 hydrogenation to formic acid on Ni (111). J Phys Chem C 2012;116:3001e6. Peng G, Sibener S, Schatz GC, Mavrikakis M. CO2 hydrogenation to formic acid on Ni (110). Surf Sci 2012;606:1050e5. Vesselli E, Rizzi M, De Rogatis L, Ding X, Baraldi A, Comelli G, et al. Hydrogen-assisted transformation of CO2 on nickel: the role of formate and carbon monoxide. J Phys Chem Lett 2009;1:402e6. Sirijaraensre J, Limtrakul J. Hydrogenation of CO2 to formic acid over a Cu-embedded graphene: a DFT study. Appl Surf Sci 2016;364:241e8. Wang J-G, Liu C-J, Zhang Y-P, Eliasson B. A DFT study of synthesis of acetic acid from methane and carbon dioxide. Chem Phys Lett 2003;368:313e8.
Please cite this article as: Hasan SZ et al., Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.09.102