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Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route
FUPROC-04426; No of Pages 7 Fuel Processing Technology xxx (2015) xxx–xxx
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Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route Chuan-Ying Liu, Rui-Ping Wei ⁎, Gao-Li Geng, Ming-Hao Zhou, Li-Jing Gao, Guo-Min Xiao ⁎ School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, PR China
a r t i c l e
i n f o
Article history: Received 31 October 2014 Received in revised form 22 January 2015 Accepted 23 January 2015 Available online xxxx Keywords: Hierarchical Y zeolite Sodium alginate Furfural hydrogenation
a b s t r a c t A series of nickel-based catalysts with the hierarchical Y zeolite, which directly synthesized using sodium alginate (SA) as the template, as support were synthesized and evaluated on the aqueous-phase hydrogenation of furfural (FFR). Effects of reaction time (RTE), reaction temperature (RTP), hydrogen pressure (HP) and catalyst amount (CA) on the conversion of FFR as well as the yield of cyclopentanone (CPON) were investigated systematically. The results indicated that the hierarchical Y zeolite catalysts exhibited evidently high catalytic activity on hydrogenation of FFR toward CPON. The highest FFR conversion was up to 96.5% with a CPON yield up to 86.5%. The synthesized hierarchical Y zeolite had high crystallinity, big BET surface area (BETSA), abundant mesopores volume and appropriate acidity. The structural and textural properties of the hierarchical Y zeolite could be controlled by the amount of template SA. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The sustained and rapid development of world economy has accelerated the demand for energy. However the fossil fuel resources are so limited as to result in high oil prices for a long time and growing pressure on energy [1]. Therefore the development of new catalytic processes for preparation of chemicals attracts more and more attention to supplement or replace those derived from petroleum [2]. At present, bio-oil derived from fast pyrolysis or liquefaction of lignocellulosic biomass, as one of the renewable energy source, is considered to replace limited fossil fuels in the future to relieve the crisis of excessive use of energy [3,4]. Bio-oil component furfural (FFR) is an important and appropriate precursor material used to produce lots of useful chemical products [5,6]. Moreover, a large number of studies have shown that the kinds of produces, such as furfuryl alcohol [7] and 2-methylfuran [8], can be prepared by vapor-phase or liquid-phase hydrogenation of FFR which is determined by different metal catalysts and solvents [9]. Cyclopentanone (CPON) is a kind of important fine chemical intermediate, as well as a raw material of pharmaceutical industry and spices. Recently, studies have shown that CPON could be prepared by the catalytic hydrogenation of FFR using water as solvent with the high selectivity. Hronec et al. [10] used various solvents (e.g., water, n-butanol, n-decanol and tetrahydrofuran) and different kinds of noble metals (e.g., Pt, Pd, Ru) catalysts to study the effect of the transformation of FFR to CPON. They used the noble metal at a relatively higher temperature of 160–175 °C with the conversion of FFR to 100% while the highest yield of CPON was only 76.5%. Besides, noble metal, as ⁎ Corresponding authors. Tel./fax: +86 25 52090612. E-mail addresses: [email protected] (R.-P. Wei), [email protected] (G.-M. Xiao).
high cost and deficient resources, is not conducive to industrial production. Nickel-based catalysts are widely used in hydrogenation because of their inexpensive price and plentiful resources [11,12]. Y zeolite, as a kind of solid acid materials with uniform microporous structure, has been widely used as catalysts because of its good hydrothermal stability and strong acidity [13,14]. However, the innate small microporous channel will limit the diffusion of reactants to reach the active sites and reaction products to break away from the active sites [15,16]. The long retention time of the reaction products on the strong acidic sits will lead to a secondary cracking and excessive by-products [17]. At last they lead to a great decrease of the target product yield. The hierarchical zeolites, which combine both the mesoporous structure advantage and the strong acidity, viewed as promising materials for catalytic applications, have attracted a great attention over the past decades [18–20]. In general, the fabrication of hierarchical zeolites can be summed up in two different approaches [21]. One method is the post-treatments, which can be approximately classified into dealumination or desilication depending on the dissolved framework constituent [22,23]. For example, dealumination is commonly performed in the synthesis of hierarchical Y zeolite since its high framework Al content [24]. But dealumination is much severer for low-Al zeolites and the process is too difficult to control, which may result in the reductive of the acid site, unordered mesoporous structure and the collapse of zeolites structure [25]. The second method is the constructive approach via a templating method using soft or hard template [21]. More and more researchers devote to directly synthesize hierarchical Y zeolite by mesoporous template method. In view of the low cost of non-noble metal and the outstanding diffusion ability of hierarchical Y zeolite, we initiated the direct hydrogenation
http://dx.doi.org/10.1016/j.fuproc.2015.01.030 0378-3820/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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of FFR to prepare CPON over the Ni-bearing hierarchical Y zeolite catalysts with high conversion and yield. Herein, we used a green and inexpensive biological agent sodium alginate (SA) as the template to successfully introduce mesoporosity in Y zeolite around 2.5 days. We further prepared the hierarchical Y zeolite supported Ni-bearing catalysts for the hydrogenation of FFR to CPON. Under the optimized reaction conditions, the FFR conversion was up to 96.4% with a CPON yield up to 86.5%. 2. Experimental 2.1. Materials All chemicals were directly used as received without any further purification. Sodium hydroxide (NaOH), sodium metaaluminate (NaAlO2), SA, ammonium chloride (NH4Cl), nickel nitrate hexahydrate (Ni(NO3)2·6H2O), FFR, CPON and cyclopentanol (CPOL) were purchased from Sinopharm Chemical Reagent Co. Ltd., China. Water glass (24.91 wt.% SiO2 and 7.25 wt.% Na2O) was purchased from Shanghai Wenhua Chemicals Co. Ltd., China. 2.2. Synthesis of hierarchical Y zeolites The synthesis procedure included two steps. The first step was preparation of the structure directing agent (SDA), the second step was the feedstock gel (FG) synthesis and crystallization under 373 K. All of the SDA were performed according to the following composition of 10.6 Na2O:1.0 Al2O3:10 SiO2:180 H2O (molar); the SDA addition percentage was 5 wt.%, which represented weight ratio of Al2O3 in SDA to overall gel (OG). In a typical synthesis of SDA, 1.01 g NaAlO2 was dissolved in the distilled water and then 3.37 g NaOH was added; after completely dissolved and cooled to room temperature, 14.87 g water glass was slowly poured under agitation for 0.5 h and further aged at 301 K for 24 h. The FG was prepared in a similar fashion to that of the seed gel except that it was used immediately without aging. After then the SDA was slowly added to obtain OG; after stirring agitation for 10 min SA was added under stirring agitation for 4 h at 301 K, and the mixture was transferred into a Teflon-lined autoclave and heated at 373 K for 25 h. After the completion of crystallization, the samples were cooled down to room temperature. The samples were washed several times with distilled water by filtration until the value of pH reach to 7–8, and after then were dried at 373 K 12 h. The OG molar composition was 4.62 Na2O:1.0 Al2O3:10.5 SiO2:180 H2O. The obtained samples were referred to as NaY-n (n = 0, 0.010, 0.014, 0.018, 0.022, 0.026), where n represented the mass ratio of SA and OG (g/g). All the assynthesized samples were calcined at 823 K for 5 h to remove the organic species. The samples were ion exchanged with a 0.2 M NH4Cl solution (liquid-to-solid ratio = 30:1 ml/g) for two times at 353 K, 1 h each time. Then the samples were washed, filtered, and dried at 373 K 12 h to get the hierarchical HY-n zeolites.
was analyzed using area normalization method by Ouhua GC 9160 equipped with a SE-54 capillary column (30 m × 0.32 mm × 0.5 μm). The temperature of the column was 130 °C, detector temperature was 280 °C, and injector temperature was 300 °C. The main product was CPON, and the FFR conversion and the product yield were calculated and defined as follows: 0 0 0 X F FR ¼ n F FR ‐n F FR =n F FR; Yi ¼ ni =n F FR where X represents conversion, Y represents yield; i represents the product in the reaction; n0FFR and nFFR depict the amounts of FFR before and after reaction, respectively, in mol; and ni is the amount of product i, in mol. 2.4. Characterization of the catalyst The powder X-ray diffraction patterns were recorded on a Rigaku D/max-A instrument with a Cu Ka radiation at 50 KV and 30 mA with a scan speed of 6°/min. SEM was recorded on a Hitachi S-4800, with an accelerating voltage of 15 KV to assess pore shape and distribution. The samples were treated by spray-gold before SEM analysis. Transmission electron microscopy (TEM) images were taken using Tecnai G2 20. The powder sample was dispersed in ethanol and kept in an ultrasonic bath for 0.5 h, then the sample was deposited onto a carbon-covered Cu supporting grid and dried at 25 °C for TEM analysis. Nitrogen adsorption/desorption isotherms were measured at 77 K with a Micromeritics ASAP-2020 analyzer after vacuum degassing the samples at 423 K for 5 h. The surface area, pore size distribution and pore volume were determined by BET (Brunauer–Emmett–Teller) and BJH (Barrett– Joyner–Halende) equations. Prior to the measurements, all the samples were degassed at 523 K for 4 h. Surface acidity of the catalysts was measured by NH3-TPD in TP-5076 apparatus at atmospheric pressure. The sample (100 mg) was preheated at 400 °C for 1 h in flowing He. 3. Results and discussion 3.1. Characterization of hierarchical NaY zeolites From Fig. 1, one can see that all NaY-n (n = 0, 0.010, 0.014, 0.018, 0.022, 0.026) samples have the same characteristic diffraction peaks of Y zeolite in the wide angle range [26]. There are no other crystal structures in the patterns, which indicts between the addition of template SA and the synthesis of Y zeolite have a good interact force well with each other. Add SA has little impact on the intensities of the diffraction peaks. The differences between the five hierarchical NaY-n (n = 0.010, 0.014, 0.018, 0.022, 0.026) samples show that the intensity of diffraction peaks is gradually enhanced when the n increased from 0.010 to 0.018.
2.3. Preparation and catalytic testing of the catalyst Ni/HY-n catalysts were prepared by impregnation method. The obtained HY-n zeolites were immersed into an aqueous solution of Ni(NO3)2·6H2O under stirring for 24 h. Then, the obtained solution was slowly evaporated and then dried at 373 K 12 h. The obtained solid was calcined at 673 K for 4 h. After grind through 80 mesh sieve, it was loaded in a tubular reactor and reduced under H2 flow at 673 K for 2 h. The aqueous-phase catalytic hydrogenation of FFR was performed in a 150 mL stainless autoclave. For a general hydrogenation reaction, 5 wt.% aqueous FFR solution and a certain amount of catalyst were loaded into the reactor vessel. Then it was filled and vented by N2 for 3 times and H2 for 3 times to exclude air. The liquid reaction mixture
Fig. 1. XRD patterns of NaY-n samples synthesized with different amounts of SA.
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
C.-Y. Liu et al. / Fuel Processing Technology xxx (2015) xxx–xxx
Because SA is the hydrophilic polymer material, the moderate amount of template SA can promote the growth of NaY zeolite leading to more silicon aluminum species growing into a complete Y zeolite structure; hence NaY-0.018 sample has better intensity of diffraction peaks. However as template SA increases to 0.026, the intensity of diffraction peaks becomes distinctly lowered and slightly broadened, suggesting that NaY-0.026 sample shows very lower crystallinity. This phenomenon indicates that hierarchical Y zeolite crystal is affected greatly by the amount of template SA under the same synthesis condition. On the other hand, the excess amount of template SA could cause the gel system to become thicker leading the interaction force between SA and silica–alumina mineral to become weaker and weaker. It results in the resistance of the crystallization of complete hierarchical Y zeolite [27, 28] and the lattice defects. From the images in Fig. 2, the typical octahedral structure is observed in the samples with a wide size range from a few tens of nanometers to submicron. The particle size of Y zeolites has changed little. But the change of the morphology of edges and corners and distribution of the particles can be observed in Fig. 2. Moreover, the image of NaY-0.018 sample shows much more clearly edges and corners and uniform distribution. But NaY-0.026 sample has obvious sleeker corners and obvious phenomenon of reunion. So it doesn't mean that the more amount of template SA is added the better morphology of hierarchical Y zeolite is obtained. Adding moderate amount of template SA can help obtain higher crystallinity and better octahedral structure of hierarchical Y zeolite under the same conditions. This result is in line with the analyzing of XRD. As demonstrated in Fig. 3a, we can see the hysteresis loops at higher relative pressure in all isotherms due to capillary condensation phenomenon proves the successful formation of mesopores [15]. It is apparent that with the increasing amount of template SA, the hysteresis loops become bigger first and smaller then. The NaY-0.018 sample presents the biggest hysteresis loop. Compared with those of hierarchical NaY-n samples, isotherm of NaY-0.026 sample shows much more steep-growing hysteresis loop. Herein we reasonably assign it to that
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having larger pore size. As seen in Fig. 3b, both hierarchical zeolite samples except NaY-0.026 sample show the peak between 10 and 30 nm in both pore size distributions which suggests the existence of mesopores. NaY-0.018 shows a bigger pore volume concentrated around 20 nm. However NaY-0.026 sample shows a larger pore size 30–50 nm which is consistent with the result of the N2 sorption isotherms. This demonstrates that there exists a balance between the amount of template SA and growth of hierarchical Y zeolite. With the increasing amount of template SA, the SA hydrogels increase that makes the pore volume become bigger. When excess amount of template SA was continuously added, the SA hydrogels can be stacked growth leading to generate disorderly bigger aperture. From Table 1, we can see that traditional NaY-0 sample has the lowest BET surface area (BETSA) (368 m2/g), pore volume (0.21 cm3/g) and almost not mesoporous. It is obvious that the BETSA and pore volume of hierarchical NaY-n (n = 0.010, 0.014, 0.018, 0.022, 0.026) samples are all larger than traditional NaY-0 sample. It demonstrates that introducing mesoporous to the traditional Y zeolite is good for enhancing the BETSA and pore volume. On the other hand, the BETSA and pore volume increase first and reduce next with the increasing amount of template SA. NaY-0.018 sample has the biggest BETSA (896 m2/g) and pore volume (0.55 cm3/g). Nevertheless, no obvious descent of the mesoporous pore volume can be seen when n = 0.014, 0.018, 0.022, indicating that the mesoporosity is maintained. Additionally, the pore volume and surface area of micropores in NaY-0.026 sample are smallest, which may be due to the decrease of pore quantity. The phenomenon is due to adding excess template SA leads to some SA hydrogel overgrowth to form aggregates resulting in the decrease of pore quantity. As shown in Fig. 4, there is a main desorption peak of NH3 at 200 °C– 300 °C which attributes to the adsorption to NH3 of the weak acid sites observed in all the samples. The intensity of weak acid site enhances first and declines next with the increasing amount of template SA, and reaches the highest level for the HY-0.018 sample. Moreover, the sample of HY-0.018 has the largest weak acid amount. It may be due to biggest BETSA and pore volume, and higher crystallinities of NaY-0.018
Fig. 2. SEM images of NaY-n: NaY-0 (a), NaY-0.010 (b), NaY-0.018 (c), and NaY-0.026 (d).
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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Fig. 3. a—N2 adsorption–desorption isotherms. b—Pore size distributions measured by BJH method.
resulting in a higher proportion of framework Al species [29]. The desorption peaks of NH3 appear at 300 °C–500 °C, which attributes to medium strong acid sites, also shown on the surface of all samples except for HY-0 and HY-0.010 samples. And traditional HY-0 sample shows only the least weak acid strength and amount over the surface. The phenomenon indicates that hierarchical Y zeolite has stronger acid strength and much more acid amount. The peak for medium strong acid sites is not very obvious over the surface of HY-0.018 sample, maybe because the large amount of weak acid amount covers the peak of medium strong acid sites on the surface. The highest medium strong acid strength and amount are obtained over the surface of HY-0.022 sample, which contributes to the highest conversion of FFR (seen from Table 2). Seen from Fig. 5, the surface of the fresh hierarchical 20wt.%Ni/HY0.018 catalyst shows smooth and no particle reunion phenomenon. But there exists some part of obvious particle on the surfaces of the fresh traditional 20wt.%Ni/HY-0 catalyst. It may be because the bigger BETSA promotes the Ni metal dispersion on the surface of the hierarchical HY-0.018. The used catalysts shows changes compared to the fresh catalysts. It can be observed obvious Y zeolite structure in the used hierarchical 20wt.%Ni/HY-0.018 catalyst with some reunion and little particle on its surface. However, the used traditional 20wt.%Ni/HY-0 catalyst shows no obvious Y zeolite structure and much of particle reunion with some compounds on its surface. It can be due to much more products and reactants depositing on its surface, reunion with Ni metal particle and destroying of the traditional HY-0 zeolite structure in the reaction. The difference between the used catalysts indicates that 20wt.%HY-0.018 catalyst with hierarchical structure shows improved stability due to the high diffusion rate of the reactant and products on the hierarchical structure of the catalyst. The morphology and microstructure of catalysts are studied further. As can be seen in Fig. 6, most of Ni particles display on the surface of Y zeolite. The Ni particles are much more homogeneously distributed with even diameters over the surface of the fresh hierarchical 20wt.%Ni/HY-0.018 catalyst than the fresh traditional 20wt.%Ni/HY-0
catalyst. It results in better catalytic activity on the hydrogenation of FFR using hierarchical 20wt.%Ni/HY-0.018 catalyst. Part of aggregated and different Ni particles size over the surface of the fresh traditional 20wt.%Ni/HY-0 catalyst are observed. After reaction, the Ni particles over the surface of the used catalysts become bigger and part aggregate together. The used traditional 20wt.%Ni/HY-0 catalyst shows obvious reunion and some velvet materials on the surface of Ni particles and the catalyst. It can be due to the smaller pore structure in the traditional 20wt.%Ni/HY-0 catalyst limits the products and reactants spreading out in time. The used hierarchical 20wt.%Ni/HY-0.018 catalyst shows that Ni particle still disperse uniformly and its surface is smooth with only little aggregation of Ni particles. It demonstrates that the hierarchical structure is not only conducive for better dispersion of Ni particles over the fresh catalysts but also to prevent the reunion and the growing of Ni particles over the used catalysts. Moreover its hierarchical structure reduces the deposit of the compounds on the surface of the catalysts and Ni particles. 3.2. Catalytic activity The catalytic performance of both the as-synthesized hierarchical Y zeolite catalysts and traditional Y zeolite catalysts were evaluated under the same catalytic condition. As could be seen from Table 2, the result shows that the main product is CPON with water as the solution leading to the furan ring rearrangement to CPON, which is consistent with the early report by Milan Hronec and Katarina Fulajtarová [10, 30] and Yang [31]. As listed in Table 2, it shows that all hierarchical 20wt.%Ni/HY-n (n = 0.010, 0.014, 0.018, 0.022) catalysts exhibit evidently higher
Table 1 Surface area and pore volume of NaY samples. Sample
SBET (m2/g)
Smic (m2/g)
SExt (m2/g)
Vtotal (cm3/g)
Vmicro (cm3/g)
Vmeso (cm3/g)
NaY-0 NaY-0.010 NaY-0.014 NaY-0.018 NaY-0.022 NaY-0.026
368 613 832 896 745 548
357 481 631 722 551 465
11 132 201 174 194 83
0.21 0.38 0.54 0.55 0.48 0.33
0.17 0.22 0.30 0.33 0.24 0.21
0.04 0.16 0.24 0.22 0.24 0.12
Fig. 4. NH3-TPD profiles of different HY-n samples.
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
C.-Y. Liu et al. / Fuel Processing Technology xxx (2015) xxx–xxx Table 2 Catalytic performance of 20wt.%Ni/HY-n catalysts was investigated on the aqueous-phase hydrogenation of FFR. Catalysts
20wt.%Ni/HY-0 20wt.%Ni/HY-0.010 20wt.%Ni/HY-0.014 20wt.%Ni/HY-0.018 20wt.%Ni/HY-0.022 20wt.%Ni/HY-0.026
Conversion (%)
88.5 94.4 95.7 96.4 99.0 73.5
Yield (%) CPON
CPOL
62.5 70.9 74.5 86.5 75.9 52.7
5.1 3.6 4.1 4.9 3.2 2.2
Reaction condition: 5 wt.% FFR solution, 1.5 wt.% catalyst, 150 °C, H2 pressure 4 MPa, 9 h.
catalytic activity on the hydrogenation of FFR toward CPON than traditional 20wt.%Ni/HY-0 catalyst. It indicts that introduction of mesopores to Y zeolite can promote the catalytic performance on the hydrogenation of FFR to CPON. This is mainly owing to the following reasons: firstly, the abundant mesopore volume in the hierarchical Y zeolite renders the reactant more conveniently diffused into the zeolite and active sites leading to high conversion of FFR; secondly, the fast diffusion rate on the hierarchical catalysts leads to less reactants and product deposition on the catalysts and the occurrence of adverse events; thirdly, the much stronger acid strength and more acid amount, and the high accessibility of acidity sites lead to the more available active sites for the reaction. 20wt.%Ni/HY-0.018 catalyst exhibits the highest catalytic activity under the same reaction condition, the conversion of FFR reaches to 96.4% and the yield of CPON reaches to 86.5%. It can be explained that the much more acid amount and abundant mesoporous offer a short diffusion path, a high diffusion rate and more accessibility of active sites [16,32] leading to CPON spreading out in a timely manner and reducing the occurrence of adverse events. 20wt.%Ni/HY-0.026 catalyst exhibits lowest catalytic activity with a conversion of FFR to 73.5% and a yield
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of CPON to 52.7% after a reaction time (RTE) of 9 h. It is mainly because of the lowest crystallinity resulting in easy collapse of the Y zeolite structure when catalysts are synthesized. The effect of RTE, reaction temperature (RTP), hydrogen pressure (HP) and catalyst amount (CA) on the conversion of FFR and product yield of aqueous-phase catalytic hydrogenation of FFR is investigated systematically by 20wt.%Ni/HY-0.018 catalyst. From Fig. 7a we can see with the extension of time that CPON is the main product from beginning to the end and its yield increases from 14.1% to 86.5%. However, in spite of the conversion of FFR increases from 96.4% to 100% when the RTE prolongs to 10 h, the yield of CPON declines to 80.9% and the yield of CPOL is up to 6.4%. This situation can be interpreted as a further hydrogenation of CPON due to the prolongation of RTE. So we chose 9 h as the optimum RTE to get better yield toward CPON in this reaction. As can be observed from Fig. 7b, conversion and yield are improved obviously when the RTP is raised from 120 °C to 150 °C; the highest yield of CPON reaches to 86.5%. However, when the temperature increases from 150 °C to 160 °C the conversion of FFR decreases a little from 96.4% to 91.3% and meanwhile the yield of CPON also decreases a lot from 86.5% to 73.3%. It could be explained by the partial decomposition of FFR during high temperature and the further hydrogenation to by-product CPOL and pentanediol [33]. Therefore the RTP has a great impact on aqueous-phase catalytic hydrogenation of FFR to CPON. As a result, we chose 150 °C as the optimum RTP to get better yield toward CPON in this reaction. As seen in Fig. 7c, the conversion of FFR increases fast from 2 MPa (42.6%) to 3 MPa (94.2%), and then it increases little but the yield of CPON increases first and falls after when the HP continually increases. It demonstrates that the relatively lower and higher HP are all not conducive to the hydrogenation of FFR to CPON. When the HP increases to 4 MPa, the yield of CPON is up to 86.5%. However, the yield of CPON decreases as the HP increases from 4 MPa to 6 MPa. It can be mainly explained by the following two reasons: firstly, some amount of hydrogen
Fig. 5. The SEM images of the fresh and used catalysts: fresh 20wt.%HY-0 catalyst (a), used 20wt.%HY-0 catalyst (b), fresh 20wt.%HY-0.018 catalyst (c), and used 20wt.%HY-0.018 catalyst (d).
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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Fig. 6. TEM images of the fresh and used catalysts: fresh 20wt.%HY-0 catalyst (a), used 20wt.%HY-0 catalyst (b), fresh 20wt.%HY-0.018 catalyst (c), and used 20wt.%HY-0.018 catalyst (d).
Fig. 7. a—Effect of reaction time on the hydrogenation of FFR. b—Effect of reaction temperature on the hydrogenation of FFR. c—Effect of reaction pressure on the hydrogenation of FFR. d—Effect of catalyst amount on the hydrogenation of FFR.
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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dissolves in the liquid phase which is all considered to the furan ring rearrangement rather than to the consecutive hydrogenation of primarily formed CPON; secondly, consecutive hydrogenation of CPON to CPOL as the yield of CPOL increases rapidly from 0.4% to 16.2% in Fig. 7c. Therefore, 4 MPa should be the optimal HP to this reaction. The CA is also one of the most important variables on the aqueousphase catalytic hydrogenation of FFR. As seen from Fig. 7d, high conversion and yield toward CPON are obtained with the increase of catalyst dosage. As it is evident from Fig. 7d with the increasing amount of CA, the yield toward CPON increases first but then almost remains unchanged, which suggests that the influence of CA on the yield of CPON is significantly different from that of the HP, the RTP, and the RTE for the catalyst studied. There is no obvious continuous improvement in conversion and yield when continuing to add the CA higher than 1.5 wt.% due to the reaction equilibrium. Hence, 1.5 wt.% is chosen as the better CA to this reaction. 4. Conclusions A facile route to synthesize nickel-based catalysts with the hierarchical Y zeolite as support was proposed for the aqueous-phase catalytic hydrogenation of FFR to CPON. Significantly larger BETSA and mesopore volume were obtained in the hierarchical Y zeolite which could be controlled by the amount of SA. The hierarchical Y zeolite catalysts showed much more improved catalytic properties than the traditional Y zeolite catalyst. The optimal reaction condition was under 150 °C of the RTP, 4.0 MPa of the initial H2 pressure, 9 h of the RTE and 1.5 wt.% catalyst. The high conversion of FFR and yield of CPON were owing to the suitable acidity of the catalysts, high diffusion rate of the reactant and products, and more accessibility of active sites on the hierarchical structure of the catalysts. Acknowledgments The authors thank the Natural Science Foundation of China (Nos. 20906013 and 21406034), Jiangsu Province Key Laboratory of Biomass Energy and Materials Open Foundation (N0.JSBEM201202), and the National Key Technology R&D Program (2012BAD32B03) for financial supports. References [1] A. Tumbalam Gooty, D. Li, C. Briens, F. Berruti, Fractional condensation of bio-oil vapors produced from birch bark pyrolysis, Separation and Purification Technology 124 (2014) 81–88. [2] D. Vargas-Hernández, J.M. Rubio-Caballero, J. Santamaría-González, R. Moreno-Tost, J.M. Mérida-Robles, M.A. Pérez-Cruz, A. Jiménez-López, R. Hernández-Huesca, P. Maireles-Torres, Furfuryl alcohol from furfural hydrogenation over copper supported on SBA-15 silica catalysts, Journal of Molecular Catalysis A: Chemical 383–384 (2014) 106–113. [3] W. Chen, Z.Y. Luo, C.J. Yu, Y. Yang, G.X. Li, J.X. Zhang, Catalytic conversion of guaiacol in ethanol for bio-oil upgrading to stable oxygenated organics, Fuel Processing Technology 126 (2014) 420–428. [4] M.H. Zhou, L.F. Tian, L. Niu, C. Li, G.M. Xiao, R. Xiao, Upgrading of liquid fuel from fast pyrolysis of biomass over modified Ni/CNT catalysts, Fuel Processing Technology 126 (2014) 12–18. [5] C.H. Xu, L.K. Zheng, J.Y. Liu, Z.Y. Huang, Furfural hydrogenation on nickel-promoted Cu-containing catalysts prepared from hydrotalcite-like precursors, Chinese Journal of Chemistry 29 (2011) 691–697. [6] Z.L. Li, S. Kelkar, C.H. Lam, K. Luczek, J.E. Jackson, D.J. Miller, C.M. Saffron, Aqueous electrocatalytic hydrogenation of furfural using a sacrificial anode, Electrochimica Acta 64 (2012) 87–93. [7] S. Sitthisa, D.E. Resasco, Hydrodeoxygenation of furfural over supported metal catalysts: a comparative study of Cu, Pd and Ni, Catalysis Letters 141 (2011) 784–791.
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Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route Chuan-Ying Liu, Rui-Ping Wei ⁎, Gao-Li Geng, Ming-Hao Zhou, Li-Jing Gao, Guo-Min Xiao ⁎ School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, PR China
a r t i c l e
i n f o
Article history: Received 31 October 2014 Received in revised form 22 January 2015 Accepted 23 January 2015 Available online xxxx Keywords: Hierarchical Y zeolite Sodium alginate Furfural hydrogenation
a b s t r a c t A series of nickel-based catalysts with the hierarchical Y zeolite, which directly synthesized using sodium alginate (SA) as the template, as support were synthesized and evaluated on the aqueous-phase hydrogenation of furfural (FFR). Effects of reaction time (RTE), reaction temperature (RTP), hydrogen pressure (HP) and catalyst amount (CA) on the conversion of FFR as well as the yield of cyclopentanone (CPON) were investigated systematically. The results indicated that the hierarchical Y zeolite catalysts exhibited evidently high catalytic activity on hydrogenation of FFR toward CPON. The highest FFR conversion was up to 96.5% with a CPON yield up to 86.5%. The synthesized hierarchical Y zeolite had high crystallinity, big BET surface area (BETSA), abundant mesopores volume and appropriate acidity. The structural and textural properties of the hierarchical Y zeolite could be controlled by the amount of template SA. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The sustained and rapid development of world economy has accelerated the demand for energy. However the fossil fuel resources are so limited as to result in high oil prices for a long time and growing pressure on energy [1]. Therefore the development of new catalytic processes for preparation of chemicals attracts more and more attention to supplement or replace those derived from petroleum [2]. At present, bio-oil derived from fast pyrolysis or liquefaction of lignocellulosic biomass, as one of the renewable energy source, is considered to replace limited fossil fuels in the future to relieve the crisis of excessive use of energy [3,4]. Bio-oil component furfural (FFR) is an important and appropriate precursor material used to produce lots of useful chemical products [5,6]. Moreover, a large number of studies have shown that the kinds of produces, such as furfuryl alcohol [7] and 2-methylfuran [8], can be prepared by vapor-phase or liquid-phase hydrogenation of FFR which is determined by different metal catalysts and solvents [9]. Cyclopentanone (CPON) is a kind of important fine chemical intermediate, as well as a raw material of pharmaceutical industry and spices. Recently, studies have shown that CPON could be prepared by the catalytic hydrogenation of FFR using water as solvent with the high selectivity. Hronec et al. [10] used various solvents (e.g., water, n-butanol, n-decanol and tetrahydrofuran) and different kinds of noble metals (e.g., Pt, Pd, Ru) catalysts to study the effect of the transformation of FFR to CPON. They used the noble metal at a relatively higher temperature of 160–175 °C with the conversion of FFR to 100% while the highest yield of CPON was only 76.5%. Besides, noble metal, as ⁎ Corresponding authors. Tel./fax: +86 25 52090612. E-mail addresses: [email protected] (R.-P. Wei), [email protected] (G.-M. Xiao).
high cost and deficient resources, is not conducive to industrial production. Nickel-based catalysts are widely used in hydrogenation because of their inexpensive price and plentiful resources [11,12]. Y zeolite, as a kind of solid acid materials with uniform microporous structure, has been widely used as catalysts because of its good hydrothermal stability and strong acidity [13,14]. However, the innate small microporous channel will limit the diffusion of reactants to reach the active sites and reaction products to break away from the active sites [15,16]. The long retention time of the reaction products on the strong acidic sits will lead to a secondary cracking and excessive by-products [17]. At last they lead to a great decrease of the target product yield. The hierarchical zeolites, which combine both the mesoporous structure advantage and the strong acidity, viewed as promising materials for catalytic applications, have attracted a great attention over the past decades [18–20]. In general, the fabrication of hierarchical zeolites can be summed up in two different approaches [21]. One method is the post-treatments, which can be approximately classified into dealumination or desilication depending on the dissolved framework constituent [22,23]. For example, dealumination is commonly performed in the synthesis of hierarchical Y zeolite since its high framework Al content [24]. But dealumination is much severer for low-Al zeolites and the process is too difficult to control, which may result in the reductive of the acid site, unordered mesoporous structure and the collapse of zeolites structure [25]. The second method is the constructive approach via a templating method using soft or hard template [21]. More and more researchers devote to directly synthesize hierarchical Y zeolite by mesoporous template method. In view of the low cost of non-noble metal and the outstanding diffusion ability of hierarchical Y zeolite, we initiated the direct hydrogenation
http://dx.doi.org/10.1016/j.fuproc.2015.01.030 0378-3820/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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of FFR to prepare CPON over the Ni-bearing hierarchical Y zeolite catalysts with high conversion and yield. Herein, we used a green and inexpensive biological agent sodium alginate (SA) as the template to successfully introduce mesoporosity in Y zeolite around 2.5 days. We further prepared the hierarchical Y zeolite supported Ni-bearing catalysts for the hydrogenation of FFR to CPON. Under the optimized reaction conditions, the FFR conversion was up to 96.4% with a CPON yield up to 86.5%. 2. Experimental 2.1. Materials All chemicals were directly used as received without any further purification. Sodium hydroxide (NaOH), sodium metaaluminate (NaAlO2), SA, ammonium chloride (NH4Cl), nickel nitrate hexahydrate (Ni(NO3)2·6H2O), FFR, CPON and cyclopentanol (CPOL) were purchased from Sinopharm Chemical Reagent Co. Ltd., China. Water glass (24.91 wt.% SiO2 and 7.25 wt.% Na2O) was purchased from Shanghai Wenhua Chemicals Co. Ltd., China. 2.2. Synthesis of hierarchical Y zeolites The synthesis procedure included two steps. The first step was preparation of the structure directing agent (SDA), the second step was the feedstock gel (FG) synthesis and crystallization under 373 K. All of the SDA were performed according to the following composition of 10.6 Na2O:1.0 Al2O3:10 SiO2:180 H2O (molar); the SDA addition percentage was 5 wt.%, which represented weight ratio of Al2O3 in SDA to overall gel (OG). In a typical synthesis of SDA, 1.01 g NaAlO2 was dissolved in the distilled water and then 3.37 g NaOH was added; after completely dissolved and cooled to room temperature, 14.87 g water glass was slowly poured under agitation for 0.5 h and further aged at 301 K for 24 h. The FG was prepared in a similar fashion to that of the seed gel except that it was used immediately without aging. After then the SDA was slowly added to obtain OG; after stirring agitation for 10 min SA was added under stirring agitation for 4 h at 301 K, and the mixture was transferred into a Teflon-lined autoclave and heated at 373 K for 25 h. After the completion of crystallization, the samples were cooled down to room temperature. The samples were washed several times with distilled water by filtration until the value of pH reach to 7–8, and after then were dried at 373 K 12 h. The OG molar composition was 4.62 Na2O:1.0 Al2O3:10.5 SiO2:180 H2O. The obtained samples were referred to as NaY-n (n = 0, 0.010, 0.014, 0.018, 0.022, 0.026), where n represented the mass ratio of SA and OG (g/g). All the assynthesized samples were calcined at 823 K for 5 h to remove the organic species. The samples were ion exchanged with a 0.2 M NH4Cl solution (liquid-to-solid ratio = 30:1 ml/g) for two times at 353 K, 1 h each time. Then the samples were washed, filtered, and dried at 373 K 12 h to get the hierarchical HY-n zeolites.
was analyzed using area normalization method by Ouhua GC 9160 equipped with a SE-54 capillary column (30 m × 0.32 mm × 0.5 μm). The temperature of the column was 130 °C, detector temperature was 280 °C, and injector temperature was 300 °C. The main product was CPON, and the FFR conversion and the product yield were calculated and defined as follows: 0 0 0 X F FR ¼ n F FR ‐n F FR =n F FR; Yi ¼ ni =n F FR where X represents conversion, Y represents yield; i represents the product in the reaction; n0FFR and nFFR depict the amounts of FFR before and after reaction, respectively, in mol; and ni is the amount of product i, in mol. 2.4. Characterization of the catalyst The powder X-ray diffraction patterns were recorded on a Rigaku D/max-A instrument with a Cu Ka radiation at 50 KV and 30 mA with a scan speed of 6°/min. SEM was recorded on a Hitachi S-4800, with an accelerating voltage of 15 KV to assess pore shape and distribution. The samples were treated by spray-gold before SEM analysis. Transmission electron microscopy (TEM) images were taken using Tecnai G2 20. The powder sample was dispersed in ethanol and kept in an ultrasonic bath for 0.5 h, then the sample was deposited onto a carbon-covered Cu supporting grid and dried at 25 °C for TEM analysis. Nitrogen adsorption/desorption isotherms were measured at 77 K with a Micromeritics ASAP-2020 analyzer after vacuum degassing the samples at 423 K for 5 h. The surface area, pore size distribution and pore volume were determined by BET (Brunauer–Emmett–Teller) and BJH (Barrett– Joyner–Halende) equations. Prior to the measurements, all the samples were degassed at 523 K for 4 h. Surface acidity of the catalysts was measured by NH3-TPD in TP-5076 apparatus at atmospheric pressure. The sample (100 mg) was preheated at 400 °C for 1 h in flowing He. 3. Results and discussion 3.1. Characterization of hierarchical NaY zeolites From Fig. 1, one can see that all NaY-n (n = 0, 0.010, 0.014, 0.018, 0.022, 0.026) samples have the same characteristic diffraction peaks of Y zeolite in the wide angle range [26]. There are no other crystal structures in the patterns, which indicts between the addition of template SA and the synthesis of Y zeolite have a good interact force well with each other. Add SA has little impact on the intensities of the diffraction peaks. The differences between the five hierarchical NaY-n (n = 0.010, 0.014, 0.018, 0.022, 0.026) samples show that the intensity of diffraction peaks is gradually enhanced when the n increased from 0.010 to 0.018.
2.3. Preparation and catalytic testing of the catalyst Ni/HY-n catalysts were prepared by impregnation method. The obtained HY-n zeolites were immersed into an aqueous solution of Ni(NO3)2·6H2O under stirring for 24 h. Then, the obtained solution was slowly evaporated and then dried at 373 K 12 h. The obtained solid was calcined at 673 K for 4 h. After grind through 80 mesh sieve, it was loaded in a tubular reactor and reduced under H2 flow at 673 K for 2 h. The aqueous-phase catalytic hydrogenation of FFR was performed in a 150 mL stainless autoclave. For a general hydrogenation reaction, 5 wt.% aqueous FFR solution and a certain amount of catalyst were loaded into the reactor vessel. Then it was filled and vented by N2 for 3 times and H2 for 3 times to exclude air. The liquid reaction mixture
Fig. 1. XRD patterns of NaY-n samples synthesized with different amounts of SA.
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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Because SA is the hydrophilic polymer material, the moderate amount of template SA can promote the growth of NaY zeolite leading to more silicon aluminum species growing into a complete Y zeolite structure; hence NaY-0.018 sample has better intensity of diffraction peaks. However as template SA increases to 0.026, the intensity of diffraction peaks becomes distinctly lowered and slightly broadened, suggesting that NaY-0.026 sample shows very lower crystallinity. This phenomenon indicates that hierarchical Y zeolite crystal is affected greatly by the amount of template SA under the same synthesis condition. On the other hand, the excess amount of template SA could cause the gel system to become thicker leading the interaction force between SA and silica–alumina mineral to become weaker and weaker. It results in the resistance of the crystallization of complete hierarchical Y zeolite [27, 28] and the lattice defects. From the images in Fig. 2, the typical octahedral structure is observed in the samples with a wide size range from a few tens of nanometers to submicron. The particle size of Y zeolites has changed little. But the change of the morphology of edges and corners and distribution of the particles can be observed in Fig. 2. Moreover, the image of NaY-0.018 sample shows much more clearly edges and corners and uniform distribution. But NaY-0.026 sample has obvious sleeker corners and obvious phenomenon of reunion. So it doesn't mean that the more amount of template SA is added the better morphology of hierarchical Y zeolite is obtained. Adding moderate amount of template SA can help obtain higher crystallinity and better octahedral structure of hierarchical Y zeolite under the same conditions. This result is in line with the analyzing of XRD. As demonstrated in Fig. 3a, we can see the hysteresis loops at higher relative pressure in all isotherms due to capillary condensation phenomenon proves the successful formation of mesopores [15]. It is apparent that with the increasing amount of template SA, the hysteresis loops become bigger first and smaller then. The NaY-0.018 sample presents the biggest hysteresis loop. Compared with those of hierarchical NaY-n samples, isotherm of NaY-0.026 sample shows much more steep-growing hysteresis loop. Herein we reasonably assign it to that
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having larger pore size. As seen in Fig. 3b, both hierarchical zeolite samples except NaY-0.026 sample show the peak between 10 and 30 nm in both pore size distributions which suggests the existence of mesopores. NaY-0.018 shows a bigger pore volume concentrated around 20 nm. However NaY-0.026 sample shows a larger pore size 30–50 nm which is consistent with the result of the N2 sorption isotherms. This demonstrates that there exists a balance between the amount of template SA and growth of hierarchical Y zeolite. With the increasing amount of template SA, the SA hydrogels increase that makes the pore volume become bigger. When excess amount of template SA was continuously added, the SA hydrogels can be stacked growth leading to generate disorderly bigger aperture. From Table 1, we can see that traditional NaY-0 sample has the lowest BET surface area (BETSA) (368 m2/g), pore volume (0.21 cm3/g) and almost not mesoporous. It is obvious that the BETSA and pore volume of hierarchical NaY-n (n = 0.010, 0.014, 0.018, 0.022, 0.026) samples are all larger than traditional NaY-0 sample. It demonstrates that introducing mesoporous to the traditional Y zeolite is good for enhancing the BETSA and pore volume. On the other hand, the BETSA and pore volume increase first and reduce next with the increasing amount of template SA. NaY-0.018 sample has the biggest BETSA (896 m2/g) and pore volume (0.55 cm3/g). Nevertheless, no obvious descent of the mesoporous pore volume can be seen when n = 0.014, 0.018, 0.022, indicating that the mesoporosity is maintained. Additionally, the pore volume and surface area of micropores in NaY-0.026 sample are smallest, which may be due to the decrease of pore quantity. The phenomenon is due to adding excess template SA leads to some SA hydrogel overgrowth to form aggregates resulting in the decrease of pore quantity. As shown in Fig. 4, there is a main desorption peak of NH3 at 200 °C– 300 °C which attributes to the adsorption to NH3 of the weak acid sites observed in all the samples. The intensity of weak acid site enhances first and declines next with the increasing amount of template SA, and reaches the highest level for the HY-0.018 sample. Moreover, the sample of HY-0.018 has the largest weak acid amount. It may be due to biggest BETSA and pore volume, and higher crystallinities of NaY-0.018
Fig. 2. SEM images of NaY-n: NaY-0 (a), NaY-0.010 (b), NaY-0.018 (c), and NaY-0.026 (d).
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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Fig. 3. a—N2 adsorption–desorption isotherms. b—Pore size distributions measured by BJH method.
resulting in a higher proportion of framework Al species [29]. The desorption peaks of NH3 appear at 300 °C–500 °C, which attributes to medium strong acid sites, also shown on the surface of all samples except for HY-0 and HY-0.010 samples. And traditional HY-0 sample shows only the least weak acid strength and amount over the surface. The phenomenon indicates that hierarchical Y zeolite has stronger acid strength and much more acid amount. The peak for medium strong acid sites is not very obvious over the surface of HY-0.018 sample, maybe because the large amount of weak acid amount covers the peak of medium strong acid sites on the surface. The highest medium strong acid strength and amount are obtained over the surface of HY-0.022 sample, which contributes to the highest conversion of FFR (seen from Table 2). Seen from Fig. 5, the surface of the fresh hierarchical 20wt.%Ni/HY0.018 catalyst shows smooth and no particle reunion phenomenon. But there exists some part of obvious particle on the surfaces of the fresh traditional 20wt.%Ni/HY-0 catalyst. It may be because the bigger BETSA promotes the Ni metal dispersion on the surface of the hierarchical HY-0.018. The used catalysts shows changes compared to the fresh catalysts. It can be observed obvious Y zeolite structure in the used hierarchical 20wt.%Ni/HY-0.018 catalyst with some reunion and little particle on its surface. However, the used traditional 20wt.%Ni/HY-0 catalyst shows no obvious Y zeolite structure and much of particle reunion with some compounds on its surface. It can be due to much more products and reactants depositing on its surface, reunion with Ni metal particle and destroying of the traditional HY-0 zeolite structure in the reaction. The difference between the used catalysts indicates that 20wt.%HY-0.018 catalyst with hierarchical structure shows improved stability due to the high diffusion rate of the reactant and products on the hierarchical structure of the catalyst. The morphology and microstructure of catalysts are studied further. As can be seen in Fig. 6, most of Ni particles display on the surface of Y zeolite. The Ni particles are much more homogeneously distributed with even diameters over the surface of the fresh hierarchical 20wt.%Ni/HY-0.018 catalyst than the fresh traditional 20wt.%Ni/HY-0
catalyst. It results in better catalytic activity on the hydrogenation of FFR using hierarchical 20wt.%Ni/HY-0.018 catalyst. Part of aggregated and different Ni particles size over the surface of the fresh traditional 20wt.%Ni/HY-0 catalyst are observed. After reaction, the Ni particles over the surface of the used catalysts become bigger and part aggregate together. The used traditional 20wt.%Ni/HY-0 catalyst shows obvious reunion and some velvet materials on the surface of Ni particles and the catalyst. It can be due to the smaller pore structure in the traditional 20wt.%Ni/HY-0 catalyst limits the products and reactants spreading out in time. The used hierarchical 20wt.%Ni/HY-0.018 catalyst shows that Ni particle still disperse uniformly and its surface is smooth with only little aggregation of Ni particles. It demonstrates that the hierarchical structure is not only conducive for better dispersion of Ni particles over the fresh catalysts but also to prevent the reunion and the growing of Ni particles over the used catalysts. Moreover its hierarchical structure reduces the deposit of the compounds on the surface of the catalysts and Ni particles. 3.2. Catalytic activity The catalytic performance of both the as-synthesized hierarchical Y zeolite catalysts and traditional Y zeolite catalysts were evaluated under the same catalytic condition. As could be seen from Table 2, the result shows that the main product is CPON with water as the solution leading to the furan ring rearrangement to CPON, which is consistent with the early report by Milan Hronec and Katarina Fulajtarová [10, 30] and Yang [31]. As listed in Table 2, it shows that all hierarchical 20wt.%Ni/HY-n (n = 0.010, 0.014, 0.018, 0.022) catalysts exhibit evidently higher
Table 1 Surface area and pore volume of NaY samples. Sample
SBET (m2/g)
Smic (m2/g)
SExt (m2/g)
Vtotal (cm3/g)
Vmicro (cm3/g)
Vmeso (cm3/g)
NaY-0 NaY-0.010 NaY-0.014 NaY-0.018 NaY-0.022 NaY-0.026
368 613 832 896 745 548
357 481 631 722 551 465
11 132 201 174 194 83
0.21 0.38 0.54 0.55 0.48 0.33
0.17 0.22 0.30 0.33 0.24 0.21
0.04 0.16 0.24 0.22 0.24 0.12
Fig. 4. NH3-TPD profiles of different HY-n samples.
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
C.-Y. Liu et al. / Fuel Processing Technology xxx (2015) xxx–xxx Table 2 Catalytic performance of 20wt.%Ni/HY-n catalysts was investigated on the aqueous-phase hydrogenation of FFR. Catalysts
20wt.%Ni/HY-0 20wt.%Ni/HY-0.010 20wt.%Ni/HY-0.014 20wt.%Ni/HY-0.018 20wt.%Ni/HY-0.022 20wt.%Ni/HY-0.026
Conversion (%)
88.5 94.4 95.7 96.4 99.0 73.5
Yield (%) CPON
CPOL
62.5 70.9 74.5 86.5 75.9 52.7
5.1 3.6 4.1 4.9 3.2 2.2
Reaction condition: 5 wt.% FFR solution, 1.5 wt.% catalyst, 150 °C, H2 pressure 4 MPa, 9 h.
catalytic activity on the hydrogenation of FFR toward CPON than traditional 20wt.%Ni/HY-0 catalyst. It indicts that introduction of mesopores to Y zeolite can promote the catalytic performance on the hydrogenation of FFR to CPON. This is mainly owing to the following reasons: firstly, the abundant mesopore volume in the hierarchical Y zeolite renders the reactant more conveniently diffused into the zeolite and active sites leading to high conversion of FFR; secondly, the fast diffusion rate on the hierarchical catalysts leads to less reactants and product deposition on the catalysts and the occurrence of adverse events; thirdly, the much stronger acid strength and more acid amount, and the high accessibility of acidity sites lead to the more available active sites for the reaction. 20wt.%Ni/HY-0.018 catalyst exhibits the highest catalytic activity under the same reaction condition, the conversion of FFR reaches to 96.4% and the yield of CPON reaches to 86.5%. It can be explained that the much more acid amount and abundant mesoporous offer a short diffusion path, a high diffusion rate and more accessibility of active sites [16,32] leading to CPON spreading out in a timely manner and reducing the occurrence of adverse events. 20wt.%Ni/HY-0.026 catalyst exhibits lowest catalytic activity with a conversion of FFR to 73.5% and a yield
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of CPON to 52.7% after a reaction time (RTE) of 9 h. It is mainly because of the lowest crystallinity resulting in easy collapse of the Y zeolite structure when catalysts are synthesized. The effect of RTE, reaction temperature (RTP), hydrogen pressure (HP) and catalyst amount (CA) on the conversion of FFR and product yield of aqueous-phase catalytic hydrogenation of FFR is investigated systematically by 20wt.%Ni/HY-0.018 catalyst. From Fig. 7a we can see with the extension of time that CPON is the main product from beginning to the end and its yield increases from 14.1% to 86.5%. However, in spite of the conversion of FFR increases from 96.4% to 100% when the RTE prolongs to 10 h, the yield of CPON declines to 80.9% and the yield of CPOL is up to 6.4%. This situation can be interpreted as a further hydrogenation of CPON due to the prolongation of RTE. So we chose 9 h as the optimum RTE to get better yield toward CPON in this reaction. As can be observed from Fig. 7b, conversion and yield are improved obviously when the RTP is raised from 120 °C to 150 °C; the highest yield of CPON reaches to 86.5%. However, when the temperature increases from 150 °C to 160 °C the conversion of FFR decreases a little from 96.4% to 91.3% and meanwhile the yield of CPON also decreases a lot from 86.5% to 73.3%. It could be explained by the partial decomposition of FFR during high temperature and the further hydrogenation to by-product CPOL and pentanediol [33]. Therefore the RTP has a great impact on aqueous-phase catalytic hydrogenation of FFR to CPON. As a result, we chose 150 °C as the optimum RTP to get better yield toward CPON in this reaction. As seen in Fig. 7c, the conversion of FFR increases fast from 2 MPa (42.6%) to 3 MPa (94.2%), and then it increases little but the yield of CPON increases first and falls after when the HP continually increases. It demonstrates that the relatively lower and higher HP are all not conducive to the hydrogenation of FFR to CPON. When the HP increases to 4 MPa, the yield of CPON is up to 86.5%. However, the yield of CPON decreases as the HP increases from 4 MPa to 6 MPa. It can be mainly explained by the following two reasons: firstly, some amount of hydrogen
Fig. 5. The SEM images of the fresh and used catalysts: fresh 20wt.%HY-0 catalyst (a), used 20wt.%HY-0 catalyst (b), fresh 20wt.%HY-0.018 catalyst (c), and used 20wt.%HY-0.018 catalyst (d).
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
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C.-Y. Liu et al. / Fuel Processing Technology xxx (2015) xxx–xxx
Fig. 6. TEM images of the fresh and used catalysts: fresh 20wt.%HY-0 catalyst (a), used 20wt.%HY-0 catalyst (b), fresh 20wt.%HY-0.018 catalyst (c), and used 20wt.%HY-0.018 catalyst (d).
Fig. 7. a—Effect of reaction time on the hydrogenation of FFR. b—Effect of reaction temperature on the hydrogenation of FFR. c—Effect of reaction pressure on the hydrogenation of FFR. d—Effect of catalyst amount on the hydrogenation of FFR.
Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030
C.-Y. Liu et al. / Fuel Processing Technology xxx (2015) xxx–xxx
dissolves in the liquid phase which is all considered to the furan ring rearrangement rather than to the consecutive hydrogenation of primarily formed CPON; secondly, consecutive hydrogenation of CPON to CPOL as the yield of CPOL increases rapidly from 0.4% to 16.2% in Fig. 7c. Therefore, 4 MPa should be the optimal HP to this reaction. The CA is also one of the most important variables on the aqueousphase catalytic hydrogenation of FFR. As seen from Fig. 7d, high conversion and yield toward CPON are obtained with the increase of catalyst dosage. As it is evident from Fig. 7d with the increasing amount of CA, the yield toward CPON increases first but then almost remains unchanged, which suggests that the influence of CA on the yield of CPON is significantly different from that of the HP, the RTP, and the RTE for the catalyst studied. There is no obvious continuous improvement in conversion and yield when continuing to add the CA higher than 1.5 wt.% due to the reaction equilibrium. Hence, 1.5 wt.% is chosen as the better CA to this reaction. 4. Conclusions A facile route to synthesize nickel-based catalysts with the hierarchical Y zeolite as support was proposed for the aqueous-phase catalytic hydrogenation of FFR to CPON. Significantly larger BETSA and mesopore volume were obtained in the hierarchical Y zeolite which could be controlled by the amount of SA. The hierarchical Y zeolite catalysts showed much more improved catalytic properties than the traditional Y zeolite catalyst. The optimal reaction condition was under 150 °C of the RTP, 4.0 MPa of the initial H2 pressure, 9 h of the RTE and 1.5 wt.% catalyst. The high conversion of FFR and yield of CPON were owing to the suitable acidity of the catalysts, high diffusion rate of the reactant and products, and more accessibility of active sites on the hierarchical structure of the catalysts. Acknowledgments The authors thank the Natural Science Foundation of China (Nos. 20906013 and 21406034), Jiangsu Province Key Laboratory of Biomass Energy and Materials Open Foundation (N0.JSBEM201202), and the National Key Technology R&D Program (2012BAD32B03) for financial supports. References [1] A. Tumbalam Gooty, D. Li, C. Briens, F. Berruti, Fractional condensation of bio-oil vapors produced from birch bark pyrolysis, Separation and Purification Technology 124 (2014) 81–88. [2] D. Vargas-Hernández, J.M. Rubio-Caballero, J. Santamaría-González, R. Moreno-Tost, J.M. Mérida-Robles, M.A. Pérez-Cruz, A. Jiménez-López, R. Hernández-Huesca, P. Maireles-Torres, Furfuryl alcohol from furfural hydrogenation over copper supported on SBA-15 silica catalysts, Journal of Molecular Catalysis A: Chemical 383–384 (2014) 106–113. [3] W. Chen, Z.Y. Luo, C.J. Yu, Y. Yang, G.X. Li, J.X. Zhang, Catalytic conversion of guaiacol in ethanol for bio-oil upgrading to stable oxygenated organics, Fuel Processing Technology 126 (2014) 420–428. [4] M.H. Zhou, L.F. Tian, L. Niu, C. Li, G.M. Xiao, R. Xiao, Upgrading of liquid fuel from fast pyrolysis of biomass over modified Ni/CNT catalysts, Fuel Processing Technology 126 (2014) 12–18. [5] C.H. Xu, L.K. Zheng, J.Y. Liu, Z.Y. Huang, Furfural hydrogenation on nickel-promoted Cu-containing catalysts prepared from hydrotalcite-like precursors, Chinese Journal of Chemistry 29 (2011) 691–697. [6] Z.L. Li, S. Kelkar, C.H. Lam, K. Luczek, J.E. Jackson, D.J. Miller, C.M. Saffron, Aqueous electrocatalytic hydrogenation of furfural using a sacrificial anode, Electrochimica Acta 64 (2012) 87–93. [7] S. Sitthisa, D.E. Resasco, Hydrodeoxygenation of furfural over supported metal catalysts: a comparative study of Cu, Pd and Ni, Catalysis Letters 141 (2011) 784–791.
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Please cite this article as: C.-Y. Liu, et al., Aqueous-phase catalytic hydrogenation of furfural over Ni-bearing hierarchical Y zeolite catalysts synthesized by a facile route, Fuel Processing Technology (2015), http://dx.doi.org/10.1016/j.fuproc.2015.01.030