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Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis
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Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis Min Hu a, Hua Wang a, Yi Wang a, Yun Zhang a,*, Jie Wu a, Bin Xu b, Daojiang Gao a, Jian Bi a, Guangyin Fan a,* a
College of Chemistry and Materials Science, Sichuan Normal University, Chengdu, 610068, PR China Key Laboratory of Green Chemistry of Sichuan Institutes of Higher Education, Sichuan University of Science and Engineering, Zigong, 643000, PR China
b
article info
abstract
Article history:
Effective catalysts for hydrogen generation from ammonia borane (AB) hydrolysis should
Received 3 June 2017
be developed for the versatile applications of hydrogen. In this study, ruthenium nano-
Received in revised form
particles (NPs) supported on alumina nanofibers (Ru/Al2O3-NFs) were synthesized by
5 August 2017
reducing the Ru(Ш) ions impregnated on Al2O3-NFs during AB hydrolysis. Results showed
Accepted 8 August 2017
that the Ru NPs with an average size of 2.9 nm were uniformly dispersed on the Al2O3-NFs
Available online xxx
support. The as-synthesized Ru/Al2O3-NFs exhibited a high turnover frequency of 327 mol H2 (mol Ru min)1 and an activation energy of 36.1 kJ mol1 for AB hydrolysis at 25 C.
Keywords:
Kinetic studies showed that the AB hydrolysis catalyzed by Ru/Al2O3-NFs was a first-order
Ammonia borane
reaction with regard to the Ru concentration and a zero-order reaction with respect to the
Ruthenium
AB concentration. The present work reveals that Ru/Al2O3-NFs show promise as a catalyst
Alumina nanofibers
in developing a highly efficient hydrogen storage system for fuel cell applications.
Hydrogen generation
© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Hydrogen is a clean, non-toxic, and abundant energy carrier that serves an alternative towards sustainable energy in the future [1e3]. Among the approaches for hydrogen production, water splitting is attractive [4]. However, the water oxidation half reaction is the bottleneck of water splitting to produce hydrogen [5e7]. Therefore, hydrogen generation from chemical hydrogen storage materials, such as sodium borohydride (NaBH4) [8,9], ammonia borane (H3NBH3, AB) [10,11], hydrazine
(N2H4$H2O) [12], and formic acid (HCOOH) [13] has been identified as a very promising strategy. Particularly, AB shows promise due to its low molecular weight (30.9 g mol1), high hydrogen content (19.6 wt%), environmental benignity, and high stability under ambient conditions [14e18]. Releasing hydrogen from AB via catalytic hydrolysis has gained attention because of the high solubility and stability of AB in the aqueous phase. Theoretically, 1 mol of AB can release 3 equivalents of hydrogen from AB hydrolysis under a suitable catalyst (Eq. (1)).
* Corresponding authors. E-mail addresses: [email protected] (Y. Zhang), [email protected] (G. Fan). http://dx.doi.org/10.1016/j.ijhydene.2017.08.051 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
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H3 NBH3 ðaqÞ þ 2H2 OðlÞ/NHþ 4 ðaqÞ þ BO2 ðaqÞ þ 3H2 ðgÞ
(1)
Numerous efforts have focused on the design and synthesis of catalysts with high activity and stability using different supports, among which Ru-based catalysts are preferable because of their high catalytic efficiency towards AB hydrolysis [19e30]. The nature of catalytic support significantly affects the performance of Ru-based catalysts. Suitable supports can prohibit the aggregation of Ru nanoparticles (NPs), thereby effectively improving their catalytic property [31]. Among the supporting materials, metal oxides, such as SiO2 [32], TiO2 [33,34], CeO2 [35], and Al2O3 [36e38] have been intensively investigated as carriers for Ru catalysts during AB hydrolysis. However, the activities of these catalysts were not satisfactory, especially the Ru catalysts on Al2O3 support. For instance, Ru catalyst supported on g-Al2O3 only had a turnover frequency (TOF) of 23.1 mol H2 (mol Ru min)1 towards AB hydrolysis [37]. RuCu/g-Al2O3 and RuCo/g-Al2O3 catalysts possessed TOFs of 16.4 and 32.9 mol H2 (mol Ru min)1, respectively [38]. The TOF of Ru@Al2O3 catalyst was 83.8 mol H2 (mol Ru min)1 [36]. Hence, developing highly active Rumetal oxide catalysts for hydrogen generation from AB hydrolysis remains challenging. Given their surface area and morphological advantages, alumina nanofibers (Al2O3-NFs) were selected in this study as a stabilizing support of Ru NPs during AB hydrolysis [39]. Ru NPs were dispersed on Al2O3-NFs by using a facile one-pot strategy under mild conditions without any external capping agent. A temperature-dependent kinetic study was performed to obtain the activation energy (Ea) of the reaction. Control experiments under different concentrations of catalyst and AB were also conducted to explore the rate law for Ru/Al2O3NF-catalyzed AB hydrolysis. Moreover, the recyclability of Ru/ Al2O3-NFs was investigated for hydrogen evolution from AB hydrolysis. The as-prepared Ru/Al2O3-NFs exhibited favorable catalytic activity for AB hydrolysis with a high TOF of 327 mol H2 (mol Ru min)1 and a low activation energy of 36.1 kJ mol1 at 25 C.
Experimental
1.7 mg/mL) was added into a two-necked-round bottom flask (25 mL) flask containing Al2O3-NFs (10.0 mg) powder and water (3.8 mL). The mixture was treated under ultrasonic for 30 min. The resulting suspension was further stirred about 30 min to ensure complete attachment of Ru (Ш) ions on the carrier. The hydrolysis of AB was performed at the same reaction flask. One neck was connected to a gas burette to detect the volume of released gas, and the other was sealed with a rubber stopper to introduce 1.0 mL of aqueous solution containing 34.2 mg of AB (AB solution). The temperature of the reaction solution was maintained at 25 C by water bath. Upon injecting the fresh AB solution into the flask, catalytic AB hydrolysis immediately began. The volume of generated hydrogen was measured by recording the displacement of water every 10 s in all experiments. For comparison, the as-synthesized Ru(Ш)/ Al2O3-NFs was firstly reduced by adding the NaBH4 aqueous solution with a NaBH4/Ru(Ш) molar ratio of 9. After the reduction, 1.0 mL of aqueous solution containing 34.2 mg of AB was introduced to the reactor. The generated hydrogen was monitored. The recyclability of Ru/Al2O3-NFs was conducted for five times. Briefly, after completing the previous run of AB hydrolysis, the catalyst was isolated through centrifugation and was washed with about 40 mL of water. The isolated catalyst was redispersed in 4 mL of aqueous solution under vigorous stirring for 30 min, and a second run of AB hydrolysis was initiated by adding another equivalent of fresh AB solution.
Characterization The morphology of Ru/Al2O3-NFs catalyst was characterized by transmission electron microscopy (TEM, FEI Tecnai G2 20) with an operating voltage of 200 kV. The crystal structure of Ru/Al2O3-NFs was investigated using the X-ray diffraction (XRD) patterns obtained with a Rigaku X-ray diffractometer D/ max-2200/PC equipped with Cu Ka radiation operating at 20 mA and 40 kV in a 2q ranging from 5 to 80 . X-ray photoelectron spectroscopy (XPS) measurement was conducted on a Thermo ESCALAB 250 Axis Ultra spectrometer using a monochromatic Al K (hy ¼ 1486.6 eV). Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis was conducted using SPECTRO ARCOS spectrometer.
Chemicals RuCl3$nH2O (Ru content: 37.0 wt%) was purchased from Kunming Institute of Precious Metal (China). AB complex (90%) was bought from Sigma-Aldrich. Al2O3-NFs with an average length of 200e300 nm and a BET surface area of 300 m2 g1 were purchased from Nanjing XFNANO Materials Tech Co., Ltd. (China). NaBH4 (99%) was bought from Aladdin Industrial Inc., China. All chemicals were commercially available and used without further purification. Ultrapure water was used in all tests.
Synthesis of Ru/Al2O3-NFs catalyst for AB hydrolysis The in situ formation of Ru/Al2O3-NFs and concomitant hydrogen generation from AB hydrolysis were performed according to the literature with some modification [40,41]. Typically, 0.2 mL of RuCl3 aqueous solution (Ru concentration:
Results and discussion Catalyst characterization The morphology and particle size of the as-prepared Ru/Al2O3NFs were investigated using TEM. The TEM images of Ru/ Al2O3-NFs in Fig. 1a and b shows that the Ru NPs with an average particle size of 2.9 nm are uniformly dispersed on the Al2O3-NFs (Fig. 1c). As well known, small-sized metal NPs are favorable for the catalytic reactivity. Therefore, it can be speculated that the Ru/Al2O3-NFs catalyst with small-sized Ru will show high catalytic activity for hydrogen evolution from AB hydrolysis. Fig. 2a shows the XRD patterns of Al2O3-NFs and the fabricated Ru/Al2O3-NFs catalyst. The XRD pattern of Al2O3NFs shows four characteristic peaks at 37.2 , 39.6 , 45.8 , and
Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
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Fig. 1 e TEM images of Ru/Al2O3-NFs (a, b). TEM images of Ru/Al2O3-NFs recycled for five times (d, e). Particle size distributions of the fresh and recycled catalysts (c, f).
66.9 , corresponding to (311), (222), (400), and (440) planes, respectively, of a typical g-Al2O3 phase (JCPDS:29-0063). The XRD pattern of Ru/Al2O3-NFs has diffraction peaks similar to those of Al2O3-NFs, indicating that the immobilization of Ru NPs does not change the crystal structure of the support. Furthermore, the peaks corresponding to Ru or Ru oxides are not detected, which is probably attributed to the low loading and high dispersion of Ru NPs.
XPS was conducted to characterize the surface compositions and chemical states of the as-prepared Ru/Al2O3-NFs. XPS survey scan of Ru/Al2O3-NFs shows the typical signals of Al, O, and Ru elements, indicating that Ru NPs are successfully stabilized on the Al2O3-NFs support. High-resolution XPS spectra of these elements were also recorded. As shown in Fig. 2b and c, the binding energies of Al2p and O1s were 74.5 eV and 531.5 eV, respectively, indicating that the support was
Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
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Fig. 2 e XRD patterns of Al2O3-NFs, Ru/Al2O3-NFs NPs and Ru/Al2O3-NFs recycled five times (a). XPS spectra of Al2p (b), O1s (c), Ru3p (d).
composed of alumina [42]. This result is consistent with the observation from XRD. The chemical state of Ru on the Al2O3NFs surface was determined by recording the spectra at the 3p region. As shown in Fig. 2d, the XPS spectrum of Ru3p in Ru/ Al2O3-NFs has two prominent peaks situated at the binding energies of 462.0 and 484.1 eV, which can be attributed to the metallic Ru 3p3/2 and Ru 3p1/2, respectively [43e45].
Catalytic activity of Ru/Al2O3-NFs for AB hydrolysis The catalytic activity of Ru/Al2O3-NFs catalyst was investigated for hydrogen evolution from AB hydrolysis at 25 C. AB hydrolysis without Ru/Al2O3-NFs showed no hydrogen evolution, indicating that the Ru species were the active sites for this reaction. Except for hydrogen, by-products, such as ammonia, were not detected, indicating that Ru/Al2O3-NFscatalyzed AB hydrolysis was highly selective to hydrogen formation. First, the reaction kinetics of AB hydrolytic dehydrogenation with Ru/Al2O3-NFs catalyst was studied by varying the Ru concentrations while keeping the other reaction conditions constant. Fig. 3a shows the plot of mol H2/mol AB versus time during Ru/Al2O3-NFs-catalyzed AB hydrolysis under different Ru concentrations at 25 C. The time required
for complete AB hydrolysis decreases with the increasing Ru concentration. However, the hydrogen generation rate is gradually decreased in the course of AB hydrolysis. This result indicates that the catalyst is not stable and deactivated during the reaction, which is assigned to the small-sized Ru NPs in Ru/Al2O3-NFs catalyst. Moreover, the catalyst poisoning could also be attributed to the formation of metaborate with increasing concentration in the course of reaction. The Ru loadings of Ru/Al2O3-NFs was determined by ICP. The ICP results show that the Ru loadings are 2.52, 3.18, 3.67 and 4.91 wt %, respectively, which are lower that the theoretical Ru loadings. These results demonstrate that Ru is not fully loaded on the support, and some of them remain in the solution. Considering the unsupported Ru also can act as active sites for AB hydrolysis, TOF values are calculated on all the Ru according to a previously reported method to compare the catalytic activities of Ru/Al2O3-NFs for AB hydrolysis [46]. For comparison, TOF value after completing the reduction of Ru was calculated from Fig. S1 since most of the reported TOF values in Table 1 were calculated with heterogeneous catalysts. It can be seen that the reduced catalyst shows a TOF of 327 mol H2 (mol Ru min)1 for hydrogen evolution from AB hydrolysis. Although this value is lower than the in-situ
Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
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Fig. 3 e The plots of mol H2/mol AB versus time for Ru/Al2O3-NFs catalyzed AB hydrolysis with different Ru concentrations at 25 C (a). The plots of hydrogen generation rate versus Ru concentration, both in logarithmic scales (b). The plots of mol H2/mol AB versus time for Ru/Al2O3-NFs catalyzed AB hydrolysis with different AB concentrations at 25 C (c). The plots of hydrogen generation rate versus the concentration of AB, both in logarithmic scales (d).
generation catalyst (TOF: 420 mol H2 (mol Ru min)1), it is still higher than most of the TOFs of previously reported Ru catalysts (Table 1). Fig. 3b shows the plot of hydrogen generation rate versus Ru concentration with both variables in logarithmic scales. The slope of the fitting line is 0.943, indicating that Ru/Al2O3-NFs-catalyzed AB hydrolysis is a first-order reaction in terms of Ru concentration. Hydrolysis was performed at various AB concentrations from 100 to 400 mM while keeping the other reaction conditions constant to study the effect of AB concentration on the catalytic activity of Ru/Al2O3-NFs. Fig. 3c shows the plot of mol H2/mol AB versus time during Ru/Al2O3-NFs-catalyzed hydrolysis under different AB concentrations at 25 C. The volume of hydrogen generation increases with the increasing AB concentration. The initial rates of hydrogen generation were calculated using the initial linear portion of the plot at different concentrations. Fig. 3d illustrates the plot of hydrogen generation rate versus AB concentration in logarithmic scales. The calculated slope of 0.43 indicates that Ru/ Al2O3-NFs-catalyzed AB hydrolysis follows zero-order kinetics in terms of AB concentration.
The effect of reaction temperature on the catalytic performance of Ru/Al2O3-NFs was further investigated under different temperatures from 20 to 35 C. As shown in Fig. 4a, the generation rate of hydrogen increases with the increasing temperature. The values of rate constant k at different temperatures were calculated from the slope of the linear portion of each plot shown in Fig. 4a to obtain the activation energy (Ea) of Ru/Al2O3-NFs-catalyzed AB hydrolysis. According to Arrhenius Equation (Eq. (2)), ln k was plotted against 1/T in Fig. 4b. The activation energy of Ru/Al2O3-NFs-catalyzed AB hydrolysis is approximately 36.1 kJ/mol, which is lower than most of previously reported results and shows the superiority of Ru/Al2O3-NFs catalyst in AB hydrolysis (Table 1). ln k ¼ Ea =RT þ ln A
(2)
The reusability of Ru/Al2O3-NFs catalyst in AB hydrolysis was also investigated and the results are shown in Fig. 4c and d. Fig. 4c shows the plot of mol H2/mol AB versus time for Ru/ Al2O3-NFs-catalyzed AB hydrolysis from the first to the fifth cycle at 25 C. As can be seen, complete AB hydrolysis is achieved with the generation of 3 equivalents of hydrogen per
Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
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Table 1 e Comparison of catalytic activity of previously reported ruthenium based catalysts applied for AB hydrolysis. Catalysts Ru/carbon Ru0/HfO2 Ru/Graphene Ru/C Ru@SiO2 Ru(0)/TiO2 Ru/TiO2(B) Ru@Al2O3 Ru/gAl2O3 RuCu(1:1)/gAl2O3 RuCo(1:1)/gAl2O3 Ru0/CeO2 Ru/TiO2 RuNi/TiO2 Ru/Al2O3-NFs a
TOF (mol Ea References H2$(molmetal$min)1) (kJ/mol) 670 170 600 429.5 200 241 303 83.3 23.1 16.4 32.9 361 604 914 327a
14.3 65 12.7 34.8 38.2 70 45.6 48 67 52 47 51 37.7 28.1 36.1
[22] [24] [25] [29] [32] [33] [34] [36] [37] [38] [38] [47] [48] [48] This work
The catalyst was firstly reduced by NaBH4 and applied as catalyst for AB hydrolysis.
mole of AB in each run. The reaction rates decreases with the increasing number of recycling, indicating that the stability of the catalyst is not substantial. However, the complete conversion of AB could be achieved in each run. Leaching tests by ICP-OES showed that Ru leaching was negligible. Therefore, the nature of the recycled catalyst was determined through XRD and TEM. As shown in Fig. 2a, the XRD pattern of the recycled catalyst is almost similar to that of the fresh catalyst, indicating that the crystal structure of the catalyst remains intact during the recycling tests. Fig. 1d and e shows the TEM images of the catalyst after recycling for five times. The morphology of Ru NPs on the surface of Al2O3-NFs remains unchanged, whereas the particle size of Ru NPs slightly increases to 3.1 nm (Fig. 1f), which corresponds to the loss of catalytic activity. Moreover, the increasing viscosity of the solution and the metaborate concentration in the successive reaction cycles could be attributed to the deactivation of the Ru/Al2O3-NFs catalyst. Further work is needed to improve the cycling stability of the Ru/Al2O3-NFs catalyst for AB hydrolysis.
Fig. 4 e The plots of mol H2/mol AB versus time for Ru/Al2O3-NFs catalyzed AB hydrolysis at different temperatures (a). Arrhenius plots of lnk versus 1/T (b). The plots of mol H2/mol AB versus time for Ru/Al2O3-NFs catalyzed AB hydrolysis with successive runs at 25 C (c). AB conversion of each recycling run (d).
Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
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Conclusions In summary, Ru NPs were dispersed on Al2O3-NFs through a facile one-pot strategy. Ru NPs with an average size of 2.9 nm were uniformly deposited on the surface of Al2O3-NFs, and consequently exhibited excellent catalytic activity for hydrogen evolution from AB hydrolysis. The catalyst had a high TOF of 327 mol H2 (mol Ru min)1 and an activation energy of 36.1 kJ mol1. The high catalytic activity of Ru/Al2O3NFs could be attributed to the small size of Ru NPs that were stabilized on the surface of Al2O3-NFs. Thus, additional active sites are available for AB hydrolysis. Kinetic studies also showed that the Al2O3-NFs-catalyzed AB hydrolysis was a first-order reaction with respect to Ru concentration and a zero-order reaction with respect to AB concentration. The asprepared Al2O3-NFs show promise as a catalyst in the development of a highly efficient hydrogen storage system for fuel cell applications.
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[10]
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Acknowledgments This work was financially supported by the Sichuan Youth Science and Technology Foundation (2016JQ0052), the Opening Project of Key Laboratory of Green Chemistry of Sichuan Institutes of Higher Education (LZJ1603), the Open Foundation of Key Laboratory of Sichuan Province Higher Education System (SWWT2015-2), the National Natural Science Foundation of China (21207109), the Scientific Research Fund of Sichuan Provincial Education Department of Sichuan Province (16TD0007).
[13]
[14]
[15]
[16]
Appendix A. Supplementary data
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Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ijhydene.2017.08.051.
[18]
references
[19]
[1] Eberle U, Felderhoff M, Schuth F. Chemical and physical solutions for hydrogen storage. Angew Chem Int Ed Eng 2009;48:6608e30. [2] Ball M, Wietschel M. The future of hydrogeneopportunities and challenges. Int J Hydrogen Energy 2009;34:615e27. [3] Schlapbach L, Zu¨ttel A. Hydrogen-storage materials for mobile applications. Nature 2001;414:353e8. ska M, Tomo T, [4] Najafpour MM, Hosseini SM, Hołyn Allakhverdiev SI. Platinum/manganese oxide nanocomposites as water-oxidizing catalysts: new findings and current controversies. Int J Hydrogen Energy 2015;40:10825e32. [5] Najafpour MM, Allakhverdiev SI. Manganese compounds as water oxidizing catalysts for hydrogen production via water splitting: from manganese complexes to nanosized manganese oxides. Int J Hydrogen Energy 2012;37:8753e64. [6] Najafpour MM, Leonard KC, Fan F-RF, Tabrizi MA, Bard AJ, King'ondu CK, et al. Nano-size layered manganese-calcium
[20]
[21]
[22]
[23]
[24]
7
oxide as an efficient and biomimetic catalyst for water oxidation under acidic conditions: comparable to platinum. Dalton Trans 2013;42:5085e91. Najafpour MM, Rahimi F, Aro E-M, Lee C-H, Allakhverdiev SI. Nano-sized manganese oxides as biomimetic catalysts for water oxidation in artificial photosynthesis: a review. J R Soc Interface 2012;9:2383. Nunes H, Ferreira M, Rangel C, Pinto A. Hydrogen generation and storage by aqueous sodium borohydride (NaBH4) hydrolysis for small portable fuel cells (H2ePEMFC). Int J Hydrogen Energy 2016;41:15426e32. Li X, Fan G, Zeng C. Synthesis of ruthenium nanoparticles deposited on graphene-like transition metal carbide as an effective catalyst for the hydrolysis of sodium borohydride. Int J Hydrogen Energy 2014;39:14927e34. Wu Z, Duan Y, Ge S, Yip ACK, Yang F, Li Y, et al. Promoting hydrolysis of ammonia borane over multiwalled carbon nanotube-supported Ru catalysts via hydrogen spillover. Catal Commun 2017;91:10e5. Demirci UB. Ammonia borane, a material with exceptional properties for chemical hydrogen storage. Int J Hydrogen Energy 2017;42:9978e10013. Wu D, Wen M, Gu C, Wu Q. 2D NiFe/CeO2 basic-siteenhanced catalyst via in-situ topotactic reduction for selectively catalyzing the H2 generation from N2H4$H2O. ACS Appl Mater Interfaces 2017;9:16103e8. Pan Y, Pan CL, Zhang Y, Li H, Min S, Guo X, et al. Selective hydrogen generation from formic acid with well-defined complexes of ruthenium and phosphorus-nitrogen PN3pincer ligand. Chem Asian J 2016;11:1357e60. Umegaki T, Yan J-M, Zhang X-B, Shioyama H, Kuriyama N, Xu Q. Boron- and nitrogen-based chemical hydrogen storage materials. Int J Hydrogen Energy 2009;34:2303e11. Wang P. Solid-state thermolysis of ammonia borane and related materials for high-capacity hydrogen storage. Dalton Trans 2012;41:4296e302. Moussa G, Moury R, Demirci UB, S‚ener T, Miele P. Boronbased hydrides for chemical hydrogen storage. Int J Energy Res 2013;37:825e42. Bandaru S, English NJ, Phillips AD, MacElroy J. Exploring promising catalysts for chemical hydrogen storage in ammonia borane: a density functional theory study. Catalysts 2017;7:140e54. Staubitz A, Robertson AP, Manners I. Ammonia-borane and related compounds as dihydrogen sources. Chem Rev 2010;110:4079e124. Fan Y, Li X, He X, Zeng C, Fan G, Liu Q, et al. Effective hydrolysis of ammonia borane catalyzed by ruthenium nanoparticles immobilized on graphic carbon nitride. Int J Hydrogen Energy 2014;39:19982e9. Fan G, Liu Q, Tang D, Li X, Bi J, Gao D. Nanodiamond supported Ru nanoparticles as an effective catalyst for hydrogen evolution from hydrolysis of ammonia borane. Int J Hydrogen Energy 2016;41:1542e9. € Durap F, Caliskan S, Ozkar S, Karakas K, Zahmakiran M. Dihydrogen phosphate stabilized ruthenium(0) nanoparticles: efficient nanocatalyst for the hydrolysis of ammonia-borane at room temperature. Materials 2015;8:4226e38. Navlani-Garcı´a M, Mori K, Nozaki A, Kuwahara Y, Yamashita H. Highly efficient Ru/carbon catalysts prepared by pyrolysis of supported Ru complex towards the hydrogen production from ammonia borane. Appl Catal A 2016;527:45e52. Zhou Q, Yang H, Xu C. Nanoporous Ru as highly efficient catalyst for hydrolysis of ammonia borane. Int J Hydrogen Energy 2016;41:12714e21. € Kalkan EB, Akbayrak S, Ozkar S. Ruthenium(0) nanoparticles supported on nanohafnia: a highly active and long-lived
Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
8
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e8
catalyst in hydrolytic dehydrogenation of ammonia borane. Mol Catal 2017;430:29e35. Du C, Ao Q, Cao N, Yang L, Luo W, Cheng G. Facile synthesis of monodisperse ruthenium nanoparticles supported on graphene for hydrogen generation from hydrolysis of ammonia borane. Int J Hydrogen Energy 2015;40:6180e7. Yang K, Zhou L, Yu G, Xiong X, Ye M, Li Y, et al. Ru nanoparticles supported on MIL-53(Cr, Al) as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane. Int J Hydrogen Energy 2016;41:6300e9. Wen L, Su J, Wu X, Cai P, Luo W, Cheng G. Ruthenium supported on MIL-96: an efficient catalyst for hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage. Int J Hydrogen Energy 2014;39:17129e35. Cao N, Liu T, Su J, Wu X, Luo W, Cheng G. Ruthenium supported on MIL-101 as an efficient catalyst for hydrogen generation from hydrolysis of amine boranes. New J Chem 2014;38:4032e5. Liang H, Chen G, Desinan S, Rosei R, Rosei F, Ma D. In situ facile synthesis of ruthenium nanocluster catalyst supported on carbon black for hydrogen generation from the hydrolysis of ammonia-borane. Int J Hydrogen Energy 2012;37:17921e7. Li X, Zeng C, Fan G. Magnetic RuCo nanoparticles supported on two-dimensional titanium carbide as highly active catalysts for the hydrolysis of ammonia borane. Int J Hydrogen Energy 2015;40:9217e24. Zhao Y, Luo Y, Yang X, Yang Y, Song Q. Tunable preparation of ruthenium nanoparticles with superior size-dependent catalytic hydrogenation properties. J Hazard Mater 2017;332:124e31. Yao Q, Shi W, Feng G, Lu Z-H, Zhang X, Tao D, et al. Ultrafine Ru nanoparticles embedded in SiO2 nanospheres: highly efficient catalysts for hydrolytic dehydrogenation of ammonia borane. J Power Sources 2014;257:293e9. € _ Ozkar Akbayrak S, Tanyıldızı S, Morkan I, S. Ruthenium(0) nanoparticles supported on nanotitania as highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane. Int J Hydrogen Energy 2014;39:9628e37. Ma Y, Li X, Zhang Y, Chen L, Wu J, Gao D, et al. Ruthenium nanoparticles supported on TiO2(B) nanotubes: effective catalysts in hydrogen evolution from the hydrolysis of ammonia borane. J Alloy Compd 2017;708:270e7. Wang R, Wang Y, Ren M, Sun G, Gao D, Chin Chong YR, et al. Effect of ceria morphology on the catalytic activity of Ru/ ceria for the dehydrogenation of ammonia borane. Int J Hydrogen Energy 2017;42:6757e64. € A facile synthesis of nearly monodisperse Can H, Metin O. ruthenium nanoparticles and their catalysis in the hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage. Appl Catal B 2012;125:304e10.
[37] Rachiero GP, Demirci UB, Miele P. Facile synthesis by polyol method of a ruthenium catalyst supported on g-Al2O3 for hydrolytic dehydrogenation of ammonia borane. Catal Today 2011;170:85e92. [38] Rachiero GP, Demirci UB, Miele P. Bimetallic RuCo and RuCu catalysts supported on g-Al2O3. A comparative study of their activity in hydrolysis of ammonia-borane. Int J Hydrogen Energy 2011;36:7051e65. [39] Chowdhury MBI, Sui R, Lucky RA, Charpentier PA. One-pot procedure to synthesize high surface area alumina nanofibers using supercritical carbon dioxide. Langmuir 2010;26:2707e13. € € [40] Ozhava D, Ozkar S. Nanoalumina-supported rhodium(0) nanoparticles as catalyst in hydrogen generation from the methanolysis of ammonia borane. Mol Catal 2017;439:50e9. € € [41] Ozhava D, Ozkar S. Rhodium(0) nanoparticles supported on nanosilica: highly active and long lived catalyst in hydrogen generation from the methanolysis of ammonia borane. Appl Catal B 2016;181:716e26. [42] Jhin J, Kang H, Byun D, Kim D, Adesida I. Reactive sputtering of Al2O3 on AlGaN/GaN heterostructure field-effect transistor. Thin Solid Films 2008;516:6483e6. [43] Zahmakiran M. Preparation and characterization of LTAtype zeolite framework dispersed ruthenium nanoparticles and their catalytic application in the hydrolytic dehydrogenation of ammoniaeborane for efficient hydrogen generation. Mater Sci Eng B 2012;177:606e13. [44] Zahmakran M, Ozkar S. Zeolite confined nanostructured dinuclear ruthenium clusters: preparation, characterization and catalytic properties in the aerobic oxidation of alcohols under mild conditions. J Mater Chem 2009;19:7112e8. [45] Ertas IE, Gulcan M, Bulut A, Yurderi M, Zahmakiran M. Metalorganic framework (MIL-101) stabilized ruthenium nanoparticles: highly efficient catalytic material in the phenol hydrogenation. Microporous Mesoporous Mater 2016;226:94e103. [46] Pachfule P, Yang X, Zhu Q-L, Tsumori N, Uchida T, Xu Q. From Ru nanoparticle-encapsulated metal-organic frameworks to highly catalytically active Cu/Ru nanoparticle-embedded porous carbon. J Mater Chem A 2017;5:4835e41. [47] Akbayrak S, Tonbul Y, Ozkar S. Ceria-supported ruthenium nanoparticles as highly active and long-lived catalysts in hydrogen generation from the hydrolysis of ammonia borane. Dalton Trans 2016;45:10969e78. [48] Mori K, Miyawaki K, Yamashita H. Ru and RueNi nanoparticles on TiO2 support as extremely active catalysts for hydrogen production from ammoniaeborane. ACS Catal 2016;6:3128e35.
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Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis Min Hu a, Hua Wang a, Yi Wang a, Yun Zhang a,*, Jie Wu a, Bin Xu b, Daojiang Gao a, Jian Bi a, Guangyin Fan a,* a
College of Chemistry and Materials Science, Sichuan Normal University, Chengdu, 610068, PR China Key Laboratory of Green Chemistry of Sichuan Institutes of Higher Education, Sichuan University of Science and Engineering, Zigong, 643000, PR China
b
article info
abstract
Article history:
Effective catalysts for hydrogen generation from ammonia borane (AB) hydrolysis should
Received 3 June 2017
be developed for the versatile applications of hydrogen. In this study, ruthenium nano-
Received in revised form
particles (NPs) supported on alumina nanofibers (Ru/Al2O3-NFs) were synthesized by
5 August 2017
reducing the Ru(Ш) ions impregnated on Al2O3-NFs during AB hydrolysis. Results showed
Accepted 8 August 2017
that the Ru NPs with an average size of 2.9 nm were uniformly dispersed on the Al2O3-NFs
Available online xxx
support. The as-synthesized Ru/Al2O3-NFs exhibited a high turnover frequency of 327 mol H2 (mol Ru min)1 and an activation energy of 36.1 kJ mol1 for AB hydrolysis at 25 C.
Keywords:
Kinetic studies showed that the AB hydrolysis catalyzed by Ru/Al2O3-NFs was a first-order
Ammonia borane
reaction with regard to the Ru concentration and a zero-order reaction with respect to the
Ruthenium
AB concentration. The present work reveals that Ru/Al2O3-NFs show promise as a catalyst
Alumina nanofibers
in developing a highly efficient hydrogen storage system for fuel cell applications.
Hydrogen generation
© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Hydrogen is a clean, non-toxic, and abundant energy carrier that serves an alternative towards sustainable energy in the future [1e3]. Among the approaches for hydrogen production, water splitting is attractive [4]. However, the water oxidation half reaction is the bottleneck of water splitting to produce hydrogen [5e7]. Therefore, hydrogen generation from chemical hydrogen storage materials, such as sodium borohydride (NaBH4) [8,9], ammonia borane (H3NBH3, AB) [10,11], hydrazine
(N2H4$H2O) [12], and formic acid (HCOOH) [13] has been identified as a very promising strategy. Particularly, AB shows promise due to its low molecular weight (30.9 g mol1), high hydrogen content (19.6 wt%), environmental benignity, and high stability under ambient conditions [14e18]. Releasing hydrogen from AB via catalytic hydrolysis has gained attention because of the high solubility and stability of AB in the aqueous phase. Theoretically, 1 mol of AB can release 3 equivalents of hydrogen from AB hydrolysis under a suitable catalyst (Eq. (1)).
* Corresponding authors. E-mail addresses: [email protected] (Y. Zhang), [email protected] (G. Fan). http://dx.doi.org/10.1016/j.ijhydene.2017.08.051 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
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H3 NBH3 ðaqÞ þ 2H2 OðlÞ/NHþ 4 ðaqÞ þ BO2 ðaqÞ þ 3H2 ðgÞ
(1)
Numerous efforts have focused on the design and synthesis of catalysts with high activity and stability using different supports, among which Ru-based catalysts are preferable because of their high catalytic efficiency towards AB hydrolysis [19e30]. The nature of catalytic support significantly affects the performance of Ru-based catalysts. Suitable supports can prohibit the aggregation of Ru nanoparticles (NPs), thereby effectively improving their catalytic property [31]. Among the supporting materials, metal oxides, such as SiO2 [32], TiO2 [33,34], CeO2 [35], and Al2O3 [36e38] have been intensively investigated as carriers for Ru catalysts during AB hydrolysis. However, the activities of these catalysts were not satisfactory, especially the Ru catalysts on Al2O3 support. For instance, Ru catalyst supported on g-Al2O3 only had a turnover frequency (TOF) of 23.1 mol H2 (mol Ru min)1 towards AB hydrolysis [37]. RuCu/g-Al2O3 and RuCo/g-Al2O3 catalysts possessed TOFs of 16.4 and 32.9 mol H2 (mol Ru min)1, respectively [38]. The TOF of Ru@Al2O3 catalyst was 83.8 mol H2 (mol Ru min)1 [36]. Hence, developing highly active Rumetal oxide catalysts for hydrogen generation from AB hydrolysis remains challenging. Given their surface area and morphological advantages, alumina nanofibers (Al2O3-NFs) were selected in this study as a stabilizing support of Ru NPs during AB hydrolysis [39]. Ru NPs were dispersed on Al2O3-NFs by using a facile one-pot strategy under mild conditions without any external capping agent. A temperature-dependent kinetic study was performed to obtain the activation energy (Ea) of the reaction. Control experiments under different concentrations of catalyst and AB were also conducted to explore the rate law for Ru/Al2O3NF-catalyzed AB hydrolysis. Moreover, the recyclability of Ru/ Al2O3-NFs was investigated for hydrogen evolution from AB hydrolysis. The as-prepared Ru/Al2O3-NFs exhibited favorable catalytic activity for AB hydrolysis with a high TOF of 327 mol H2 (mol Ru min)1 and a low activation energy of 36.1 kJ mol1 at 25 C.
Experimental
1.7 mg/mL) was added into a two-necked-round bottom flask (25 mL) flask containing Al2O3-NFs (10.0 mg) powder and water (3.8 mL). The mixture was treated under ultrasonic for 30 min. The resulting suspension was further stirred about 30 min to ensure complete attachment of Ru (Ш) ions on the carrier. The hydrolysis of AB was performed at the same reaction flask. One neck was connected to a gas burette to detect the volume of released gas, and the other was sealed with a rubber stopper to introduce 1.0 mL of aqueous solution containing 34.2 mg of AB (AB solution). The temperature of the reaction solution was maintained at 25 C by water bath. Upon injecting the fresh AB solution into the flask, catalytic AB hydrolysis immediately began. The volume of generated hydrogen was measured by recording the displacement of water every 10 s in all experiments. For comparison, the as-synthesized Ru(Ш)/ Al2O3-NFs was firstly reduced by adding the NaBH4 aqueous solution with a NaBH4/Ru(Ш) molar ratio of 9. After the reduction, 1.0 mL of aqueous solution containing 34.2 mg of AB was introduced to the reactor. The generated hydrogen was monitored. The recyclability of Ru/Al2O3-NFs was conducted for five times. Briefly, after completing the previous run of AB hydrolysis, the catalyst was isolated through centrifugation and was washed with about 40 mL of water. The isolated catalyst was redispersed in 4 mL of aqueous solution under vigorous stirring for 30 min, and a second run of AB hydrolysis was initiated by adding another equivalent of fresh AB solution.
Characterization The morphology of Ru/Al2O3-NFs catalyst was characterized by transmission electron microscopy (TEM, FEI Tecnai G2 20) with an operating voltage of 200 kV. The crystal structure of Ru/Al2O3-NFs was investigated using the X-ray diffraction (XRD) patterns obtained with a Rigaku X-ray diffractometer D/ max-2200/PC equipped with Cu Ka radiation operating at 20 mA and 40 kV in a 2q ranging from 5 to 80 . X-ray photoelectron spectroscopy (XPS) measurement was conducted on a Thermo ESCALAB 250 Axis Ultra spectrometer using a monochromatic Al K (hy ¼ 1486.6 eV). Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis was conducted using SPECTRO ARCOS spectrometer.
Chemicals RuCl3$nH2O (Ru content: 37.0 wt%) was purchased from Kunming Institute of Precious Metal (China). AB complex (90%) was bought from Sigma-Aldrich. Al2O3-NFs with an average length of 200e300 nm and a BET surface area of 300 m2 g1 were purchased from Nanjing XFNANO Materials Tech Co., Ltd. (China). NaBH4 (99%) was bought from Aladdin Industrial Inc., China. All chemicals were commercially available and used without further purification. Ultrapure water was used in all tests.
Synthesis of Ru/Al2O3-NFs catalyst for AB hydrolysis The in situ formation of Ru/Al2O3-NFs and concomitant hydrogen generation from AB hydrolysis were performed according to the literature with some modification [40,41]. Typically, 0.2 mL of RuCl3 aqueous solution (Ru concentration:
Results and discussion Catalyst characterization The morphology and particle size of the as-prepared Ru/Al2O3NFs were investigated using TEM. The TEM images of Ru/ Al2O3-NFs in Fig. 1a and b shows that the Ru NPs with an average particle size of 2.9 nm are uniformly dispersed on the Al2O3-NFs (Fig. 1c). As well known, small-sized metal NPs are favorable for the catalytic reactivity. Therefore, it can be speculated that the Ru/Al2O3-NFs catalyst with small-sized Ru will show high catalytic activity for hydrogen evolution from AB hydrolysis. Fig. 2a shows the XRD patterns of Al2O3-NFs and the fabricated Ru/Al2O3-NFs catalyst. The XRD pattern of Al2O3NFs shows four characteristic peaks at 37.2 , 39.6 , 45.8 , and
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Fig. 1 e TEM images of Ru/Al2O3-NFs (a, b). TEM images of Ru/Al2O3-NFs recycled for five times (d, e). Particle size distributions of the fresh and recycled catalysts (c, f).
66.9 , corresponding to (311), (222), (400), and (440) planes, respectively, of a typical g-Al2O3 phase (JCPDS:29-0063). The XRD pattern of Ru/Al2O3-NFs has diffraction peaks similar to those of Al2O3-NFs, indicating that the immobilization of Ru NPs does not change the crystal structure of the support. Furthermore, the peaks corresponding to Ru or Ru oxides are not detected, which is probably attributed to the low loading and high dispersion of Ru NPs.
XPS was conducted to characterize the surface compositions and chemical states of the as-prepared Ru/Al2O3-NFs. XPS survey scan of Ru/Al2O3-NFs shows the typical signals of Al, O, and Ru elements, indicating that Ru NPs are successfully stabilized on the Al2O3-NFs support. High-resolution XPS spectra of these elements were also recorded. As shown in Fig. 2b and c, the binding energies of Al2p and O1s were 74.5 eV and 531.5 eV, respectively, indicating that the support was
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Fig. 2 e XRD patterns of Al2O3-NFs, Ru/Al2O3-NFs NPs and Ru/Al2O3-NFs recycled five times (a). XPS spectra of Al2p (b), O1s (c), Ru3p (d).
composed of alumina [42]. This result is consistent with the observation from XRD. The chemical state of Ru on the Al2O3NFs surface was determined by recording the spectra at the 3p region. As shown in Fig. 2d, the XPS spectrum of Ru3p in Ru/ Al2O3-NFs has two prominent peaks situated at the binding energies of 462.0 and 484.1 eV, which can be attributed to the metallic Ru 3p3/2 and Ru 3p1/2, respectively [43e45].
Catalytic activity of Ru/Al2O3-NFs for AB hydrolysis The catalytic activity of Ru/Al2O3-NFs catalyst was investigated for hydrogen evolution from AB hydrolysis at 25 C. AB hydrolysis without Ru/Al2O3-NFs showed no hydrogen evolution, indicating that the Ru species were the active sites for this reaction. Except for hydrogen, by-products, such as ammonia, were not detected, indicating that Ru/Al2O3-NFscatalyzed AB hydrolysis was highly selective to hydrogen formation. First, the reaction kinetics of AB hydrolytic dehydrogenation with Ru/Al2O3-NFs catalyst was studied by varying the Ru concentrations while keeping the other reaction conditions constant. Fig. 3a shows the plot of mol H2/mol AB versus time during Ru/Al2O3-NFs-catalyzed AB hydrolysis under different Ru concentrations at 25 C. The time required
for complete AB hydrolysis decreases with the increasing Ru concentration. However, the hydrogen generation rate is gradually decreased in the course of AB hydrolysis. This result indicates that the catalyst is not stable and deactivated during the reaction, which is assigned to the small-sized Ru NPs in Ru/Al2O3-NFs catalyst. Moreover, the catalyst poisoning could also be attributed to the formation of metaborate with increasing concentration in the course of reaction. The Ru loadings of Ru/Al2O3-NFs was determined by ICP. The ICP results show that the Ru loadings are 2.52, 3.18, 3.67 and 4.91 wt %, respectively, which are lower that the theoretical Ru loadings. These results demonstrate that Ru is not fully loaded on the support, and some of them remain in the solution. Considering the unsupported Ru also can act as active sites for AB hydrolysis, TOF values are calculated on all the Ru according to a previously reported method to compare the catalytic activities of Ru/Al2O3-NFs for AB hydrolysis [46]. For comparison, TOF value after completing the reduction of Ru was calculated from Fig. S1 since most of the reported TOF values in Table 1 were calculated with heterogeneous catalysts. It can be seen that the reduced catalyst shows a TOF of 327 mol H2 (mol Ru min)1 for hydrogen evolution from AB hydrolysis. Although this value is lower than the in-situ
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Fig. 3 e The plots of mol H2/mol AB versus time for Ru/Al2O3-NFs catalyzed AB hydrolysis with different Ru concentrations at 25 C (a). The plots of hydrogen generation rate versus Ru concentration, both in logarithmic scales (b). The plots of mol H2/mol AB versus time for Ru/Al2O3-NFs catalyzed AB hydrolysis with different AB concentrations at 25 C (c). The plots of hydrogen generation rate versus the concentration of AB, both in logarithmic scales (d).
generation catalyst (TOF: 420 mol H2 (mol Ru min)1), it is still higher than most of the TOFs of previously reported Ru catalysts (Table 1). Fig. 3b shows the plot of hydrogen generation rate versus Ru concentration with both variables in logarithmic scales. The slope of the fitting line is 0.943, indicating that Ru/Al2O3-NFs-catalyzed AB hydrolysis is a first-order reaction in terms of Ru concentration. Hydrolysis was performed at various AB concentrations from 100 to 400 mM while keeping the other reaction conditions constant to study the effect of AB concentration on the catalytic activity of Ru/Al2O3-NFs. Fig. 3c shows the plot of mol H2/mol AB versus time during Ru/Al2O3-NFs-catalyzed hydrolysis under different AB concentrations at 25 C. The volume of hydrogen generation increases with the increasing AB concentration. The initial rates of hydrogen generation were calculated using the initial linear portion of the plot at different concentrations. Fig. 3d illustrates the plot of hydrogen generation rate versus AB concentration in logarithmic scales. The calculated slope of 0.43 indicates that Ru/ Al2O3-NFs-catalyzed AB hydrolysis follows zero-order kinetics in terms of AB concentration.
The effect of reaction temperature on the catalytic performance of Ru/Al2O3-NFs was further investigated under different temperatures from 20 to 35 C. As shown in Fig. 4a, the generation rate of hydrogen increases with the increasing temperature. The values of rate constant k at different temperatures were calculated from the slope of the linear portion of each plot shown in Fig. 4a to obtain the activation energy (Ea) of Ru/Al2O3-NFs-catalyzed AB hydrolysis. According to Arrhenius Equation (Eq. (2)), ln k was plotted against 1/T in Fig. 4b. The activation energy of Ru/Al2O3-NFs-catalyzed AB hydrolysis is approximately 36.1 kJ/mol, which is lower than most of previously reported results and shows the superiority of Ru/Al2O3-NFs catalyst in AB hydrolysis (Table 1). ln k ¼ Ea =RT þ ln A
(2)
The reusability of Ru/Al2O3-NFs catalyst in AB hydrolysis was also investigated and the results are shown in Fig. 4c and d. Fig. 4c shows the plot of mol H2/mol AB versus time for Ru/ Al2O3-NFs-catalyzed AB hydrolysis from the first to the fifth cycle at 25 C. As can be seen, complete AB hydrolysis is achieved with the generation of 3 equivalents of hydrogen per
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Table 1 e Comparison of catalytic activity of previously reported ruthenium based catalysts applied for AB hydrolysis. Catalysts Ru/carbon Ru0/HfO2 Ru/Graphene Ru/C Ru@SiO2 Ru(0)/TiO2 Ru/TiO2(B) Ru@Al2O3 Ru/gAl2O3 RuCu(1:1)/gAl2O3 RuCo(1:1)/gAl2O3 Ru0/CeO2 Ru/TiO2 RuNi/TiO2 Ru/Al2O3-NFs a
TOF (mol Ea References H2$(molmetal$min)1) (kJ/mol) 670 170 600 429.5 200 241 303 83.3 23.1 16.4 32.9 361 604 914 327a
14.3 65 12.7 34.8 38.2 70 45.6 48 67 52 47 51 37.7 28.1 36.1
[22] [24] [25] [29] [32] [33] [34] [36] [37] [38] [38] [47] [48] [48] This work
The catalyst was firstly reduced by NaBH4 and applied as catalyst for AB hydrolysis.
mole of AB in each run. The reaction rates decreases with the increasing number of recycling, indicating that the stability of the catalyst is not substantial. However, the complete conversion of AB could be achieved in each run. Leaching tests by ICP-OES showed that Ru leaching was negligible. Therefore, the nature of the recycled catalyst was determined through XRD and TEM. As shown in Fig. 2a, the XRD pattern of the recycled catalyst is almost similar to that of the fresh catalyst, indicating that the crystal structure of the catalyst remains intact during the recycling tests. Fig. 1d and e shows the TEM images of the catalyst after recycling for five times. The morphology of Ru NPs on the surface of Al2O3-NFs remains unchanged, whereas the particle size of Ru NPs slightly increases to 3.1 nm (Fig. 1f), which corresponds to the loss of catalytic activity. Moreover, the increasing viscosity of the solution and the metaborate concentration in the successive reaction cycles could be attributed to the deactivation of the Ru/Al2O3-NFs catalyst. Further work is needed to improve the cycling stability of the Ru/Al2O3-NFs catalyst for AB hydrolysis.
Fig. 4 e The plots of mol H2/mol AB versus time for Ru/Al2O3-NFs catalyzed AB hydrolysis at different temperatures (a). Arrhenius plots of lnk versus 1/T (b). The plots of mol H2/mol AB versus time for Ru/Al2O3-NFs catalyzed AB hydrolysis with successive runs at 25 C (c). AB conversion of each recycling run (d).
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Conclusions In summary, Ru NPs were dispersed on Al2O3-NFs through a facile one-pot strategy. Ru NPs with an average size of 2.9 nm were uniformly deposited on the surface of Al2O3-NFs, and consequently exhibited excellent catalytic activity for hydrogen evolution from AB hydrolysis. The catalyst had a high TOF of 327 mol H2 (mol Ru min)1 and an activation energy of 36.1 kJ mol1. The high catalytic activity of Ru/Al2O3NFs could be attributed to the small size of Ru NPs that were stabilized on the surface of Al2O3-NFs. Thus, additional active sites are available for AB hydrolysis. Kinetic studies also showed that the Al2O3-NFs-catalyzed AB hydrolysis was a first-order reaction with respect to Ru concentration and a zero-order reaction with respect to AB concentration. The asprepared Al2O3-NFs show promise as a catalyst in the development of a highly efficient hydrogen storage system for fuel cell applications.
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Acknowledgments This work was financially supported by the Sichuan Youth Science and Technology Foundation (2016JQ0052), the Opening Project of Key Laboratory of Green Chemistry of Sichuan Institutes of Higher Education (LZJ1603), the Open Foundation of Key Laboratory of Sichuan Province Higher Education System (SWWT2015-2), the National Natural Science Foundation of China (21207109), the Scientific Research Fund of Sichuan Provincial Education Department of Sichuan Province (16TD0007).
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Appendix A. Supplementary data
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Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ijhydene.2017.08.051.
[18]
references
[19]
[1] Eberle U, Felderhoff M, Schuth F. Chemical and physical solutions for hydrogen storage. Angew Chem Int Ed Eng 2009;48:6608e30. [2] Ball M, Wietschel M. The future of hydrogeneopportunities and challenges. Int J Hydrogen Energy 2009;34:615e27. [3] Schlapbach L, Zu¨ttel A. Hydrogen-storage materials for mobile applications. Nature 2001;414:353e8. ska M, Tomo T, [4] Najafpour MM, Hosseini SM, Hołyn Allakhverdiev SI. Platinum/manganese oxide nanocomposites as water-oxidizing catalysts: new findings and current controversies. Int J Hydrogen Energy 2015;40:10825e32. [5] Najafpour MM, Allakhverdiev SI. Manganese compounds as water oxidizing catalysts for hydrogen production via water splitting: from manganese complexes to nanosized manganese oxides. Int J Hydrogen Energy 2012;37:8753e64. [6] Najafpour MM, Leonard KC, Fan F-RF, Tabrizi MA, Bard AJ, King'ondu CK, et al. Nano-size layered manganese-calcium
[20]
[21]
[22]
[23]
[24]
7
oxide as an efficient and biomimetic catalyst for water oxidation under acidic conditions: comparable to platinum. Dalton Trans 2013;42:5085e91. Najafpour MM, Rahimi F, Aro E-M, Lee C-H, Allakhverdiev SI. Nano-sized manganese oxides as biomimetic catalysts for water oxidation in artificial photosynthesis: a review. J R Soc Interface 2012;9:2383. Nunes H, Ferreira M, Rangel C, Pinto A. Hydrogen generation and storage by aqueous sodium borohydride (NaBH4) hydrolysis for small portable fuel cells (H2ePEMFC). Int J Hydrogen Energy 2016;41:15426e32. Li X, Fan G, Zeng C. Synthesis of ruthenium nanoparticles deposited on graphene-like transition metal carbide as an effective catalyst for the hydrolysis of sodium borohydride. Int J Hydrogen Energy 2014;39:14927e34. Wu Z, Duan Y, Ge S, Yip ACK, Yang F, Li Y, et al. Promoting hydrolysis of ammonia borane over multiwalled carbon nanotube-supported Ru catalysts via hydrogen spillover. Catal Commun 2017;91:10e5. Demirci UB. Ammonia borane, a material with exceptional properties for chemical hydrogen storage. Int J Hydrogen Energy 2017;42:9978e10013. Wu D, Wen M, Gu C, Wu Q. 2D NiFe/CeO2 basic-siteenhanced catalyst via in-situ topotactic reduction for selectively catalyzing the H2 generation from N2H4$H2O. ACS Appl Mater Interfaces 2017;9:16103e8. Pan Y, Pan CL, Zhang Y, Li H, Min S, Guo X, et al. Selective hydrogen generation from formic acid with well-defined complexes of ruthenium and phosphorus-nitrogen PN3pincer ligand. Chem Asian J 2016;11:1357e60. Umegaki T, Yan J-M, Zhang X-B, Shioyama H, Kuriyama N, Xu Q. Boron- and nitrogen-based chemical hydrogen storage materials. Int J Hydrogen Energy 2009;34:2303e11. Wang P. Solid-state thermolysis of ammonia borane and related materials for high-capacity hydrogen storage. Dalton Trans 2012;41:4296e302. Moussa G, Moury R, Demirci UB, S‚ener T, Miele P. Boronbased hydrides for chemical hydrogen storage. Int J Energy Res 2013;37:825e42. Bandaru S, English NJ, Phillips AD, MacElroy J. Exploring promising catalysts for chemical hydrogen storage in ammonia borane: a density functional theory study. Catalysts 2017;7:140e54. Staubitz A, Robertson AP, Manners I. Ammonia-borane and related compounds as dihydrogen sources. Chem Rev 2010;110:4079e124. Fan Y, Li X, He X, Zeng C, Fan G, Liu Q, et al. Effective hydrolysis of ammonia borane catalyzed by ruthenium nanoparticles immobilized on graphic carbon nitride. Int J Hydrogen Energy 2014;39:19982e9. Fan G, Liu Q, Tang D, Li X, Bi J, Gao D. Nanodiamond supported Ru nanoparticles as an effective catalyst for hydrogen evolution from hydrolysis of ammonia borane. Int J Hydrogen Energy 2016;41:1542e9. € Durap F, Caliskan S, Ozkar S, Karakas K, Zahmakiran M. Dihydrogen phosphate stabilized ruthenium(0) nanoparticles: efficient nanocatalyst for the hydrolysis of ammonia-borane at room temperature. Materials 2015;8:4226e38. Navlani-Garcı´a M, Mori K, Nozaki A, Kuwahara Y, Yamashita H. Highly efficient Ru/carbon catalysts prepared by pyrolysis of supported Ru complex towards the hydrogen production from ammonia borane. Appl Catal A 2016;527:45e52. Zhou Q, Yang H, Xu C. Nanoporous Ru as highly efficient catalyst for hydrolysis of ammonia borane. Int J Hydrogen Energy 2016;41:12714e21. € Kalkan EB, Akbayrak S, Ozkar S. Ruthenium(0) nanoparticles supported on nanohafnia: a highly active and long-lived
Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051
8
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e8
catalyst in hydrolytic dehydrogenation of ammonia borane. Mol Catal 2017;430:29e35. Du C, Ao Q, Cao N, Yang L, Luo W, Cheng G. Facile synthesis of monodisperse ruthenium nanoparticles supported on graphene for hydrogen generation from hydrolysis of ammonia borane. Int J Hydrogen Energy 2015;40:6180e7. Yang K, Zhou L, Yu G, Xiong X, Ye M, Li Y, et al. Ru nanoparticles supported on MIL-53(Cr, Al) as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane. Int J Hydrogen Energy 2016;41:6300e9. Wen L, Su J, Wu X, Cai P, Luo W, Cheng G. Ruthenium supported on MIL-96: an efficient catalyst for hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage. Int J Hydrogen Energy 2014;39:17129e35. Cao N, Liu T, Su J, Wu X, Luo W, Cheng G. Ruthenium supported on MIL-101 as an efficient catalyst for hydrogen generation from hydrolysis of amine boranes. New J Chem 2014;38:4032e5. Liang H, Chen G, Desinan S, Rosei R, Rosei F, Ma D. In situ facile synthesis of ruthenium nanocluster catalyst supported on carbon black for hydrogen generation from the hydrolysis of ammonia-borane. Int J Hydrogen Energy 2012;37:17921e7. Li X, Zeng C, Fan G. Magnetic RuCo nanoparticles supported on two-dimensional titanium carbide as highly active catalysts for the hydrolysis of ammonia borane. Int J Hydrogen Energy 2015;40:9217e24. Zhao Y, Luo Y, Yang X, Yang Y, Song Q. Tunable preparation of ruthenium nanoparticles with superior size-dependent catalytic hydrogenation properties. J Hazard Mater 2017;332:124e31. Yao Q, Shi W, Feng G, Lu Z-H, Zhang X, Tao D, et al. Ultrafine Ru nanoparticles embedded in SiO2 nanospheres: highly efficient catalysts for hydrolytic dehydrogenation of ammonia borane. J Power Sources 2014;257:293e9. € _ Ozkar Akbayrak S, Tanyıldızı S, Morkan I, S. Ruthenium(0) nanoparticles supported on nanotitania as highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane. Int J Hydrogen Energy 2014;39:9628e37. Ma Y, Li X, Zhang Y, Chen L, Wu J, Gao D, et al. Ruthenium nanoparticles supported on TiO2(B) nanotubes: effective catalysts in hydrogen evolution from the hydrolysis of ammonia borane. J Alloy Compd 2017;708:270e7. Wang R, Wang Y, Ren M, Sun G, Gao D, Chin Chong YR, et al. Effect of ceria morphology on the catalytic activity of Ru/ ceria for the dehydrogenation of ammonia borane. Int J Hydrogen Energy 2017;42:6757e64. € A facile synthesis of nearly monodisperse Can H, Metin O. ruthenium nanoparticles and their catalysis in the hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage. Appl Catal B 2012;125:304e10.
[37] Rachiero GP, Demirci UB, Miele P. Facile synthesis by polyol method of a ruthenium catalyst supported on g-Al2O3 for hydrolytic dehydrogenation of ammonia borane. Catal Today 2011;170:85e92. [38] Rachiero GP, Demirci UB, Miele P. Bimetallic RuCo and RuCu catalysts supported on g-Al2O3. A comparative study of their activity in hydrolysis of ammonia-borane. Int J Hydrogen Energy 2011;36:7051e65. [39] Chowdhury MBI, Sui R, Lucky RA, Charpentier PA. One-pot procedure to synthesize high surface area alumina nanofibers using supercritical carbon dioxide. Langmuir 2010;26:2707e13. € € [40] Ozhava D, Ozkar S. Nanoalumina-supported rhodium(0) nanoparticles as catalyst in hydrogen generation from the methanolysis of ammonia borane. Mol Catal 2017;439:50e9. € € [41] Ozhava D, Ozkar S. Rhodium(0) nanoparticles supported on nanosilica: highly active and long lived catalyst in hydrogen generation from the methanolysis of ammonia borane. Appl Catal B 2016;181:716e26. [42] Jhin J, Kang H, Byun D, Kim D, Adesida I. Reactive sputtering of Al2O3 on AlGaN/GaN heterostructure field-effect transistor. Thin Solid Films 2008;516:6483e6. [43] Zahmakiran M. Preparation and characterization of LTAtype zeolite framework dispersed ruthenium nanoparticles and their catalytic application in the hydrolytic dehydrogenation of ammoniaeborane for efficient hydrogen generation. Mater Sci Eng B 2012;177:606e13. [44] Zahmakran M, Ozkar S. Zeolite confined nanostructured dinuclear ruthenium clusters: preparation, characterization and catalytic properties in the aerobic oxidation of alcohols under mild conditions. J Mater Chem 2009;19:7112e8. [45] Ertas IE, Gulcan M, Bulut A, Yurderi M, Zahmakiran M. Metalorganic framework (MIL-101) stabilized ruthenium nanoparticles: highly efficient catalytic material in the phenol hydrogenation. Microporous Mesoporous Mater 2016;226:94e103. [46] Pachfule P, Yang X, Zhu Q-L, Tsumori N, Uchida T, Xu Q. From Ru nanoparticle-encapsulated metal-organic frameworks to highly catalytically active Cu/Ru nanoparticle-embedded porous carbon. J Mater Chem A 2017;5:4835e41. [47] Akbayrak S, Tonbul Y, Ozkar S. Ceria-supported ruthenium nanoparticles as highly active and long-lived catalysts in hydrogen generation from the hydrolysis of ammonia borane. Dalton Trans 2016;45:10969e78. [48] Mori K, Miyawaki K, Yamashita H. Ru and RueNi nanoparticles on TiO2 support as extremely active catalysts for hydrogen production from ammoniaeborane. ACS Catal 2016;6:3128e35.
Please cite this article in press as: Hu M, et al., Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis, International Journal of Hydrogen Energy (2017), http://dx.doi.org/ 10.1016/j.ijhydene.2017.08.051