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Catalysts 2017, 7(4), 125; https://doi.org/10.3390/catal7040125

Article
Preparation of Rh/Ni Bimetallic Nanoparticles and Their Catalytic Activities for Hydrogen Generation from Hydrolysis of KBH4
1
The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China
2
Hubei Key Laboratory for Efficient Utilization and Agglomeration of Metallurgical Mineral Resources, Wuhan University of Science and Technology, Wuhan 430081, China
3
School of Chemistry and Chemical Engineering, Wuhan University of Science and Technology, Wuhan 430081, China
4
Hubei Province Key Laboratory of Science in Metallurgical Process, Wuhan University of Science and Technology, Wuhan 430081, China
*
Authors to whom correspondence should be addressed.
Academic Editor: Rajendra S. Ghadwal
Received: 20 March 2017 / Accepted: 18 April 2017 / Published: 23 April 2017

Abstract

:
ISOBAM-104 protected Rh/Ni bimetallic nanoparticles (BNPs) of 3.1 nm in diameter were synthesized by a co-reduction method with a rapid injection of KBH4 solution. The catalytic activities of as-prepared BNPs for hydrogen generation from hydrolysis of a basic KBH4 solution were evaluated. Ultraviolet-visible spectrophotometry (UV-Vis), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the structure, particle size, and chemical composition of the resultant BNPs. Catalytic activities for hydrolysis of KBH4 and catalytic kinetics of prepared BNPs were also investigated. It was shown that Rh/Ni BNPs displayed much higher catalytic activities than that of Rh or Ni monometallic nanoparticles (MNPs), and the prepared Rh10Ni90 BNPs possessed the highest catalytic activities, with a value of 11,580 mol-H2·h−1·mol-Rh−1. The high catalytic activities of Rh/Ni BNPs could be attributed to the electron transfer effect between Rh and Ni atoms, which was confirmed by a density functional theory (DFT) calculation. The apparent activation energy for hydrogen generation of the prepared Rh10Ni90 BNPs was about 47.2 ± 2.1 kJ/mol, according to a kinetic study.
Keywords:
Rh/Ni BNPs; hydrogen generation; catalytic activities; electron transfer effect

1. Introduction

Hydrogen is one of many potential alternatives to replace nonrenewable fuel sources that are used nowadays, as it is an environmentally-friendly and renewable energy carrier. However, the technique for hydrogen storage is still a large problem which hinders the application of hydrogen. To date, an extensive body of research has been published on hydrogen storage including liquid hydrogen storage, high pressure gaseous hydrogen storage, adsorption hydrogen storage, metal hydride hydrogen storage, organic compounds hydrogen storage, and liquid phase chemical hydrogen storage [1,2,3,4]. Among these methods, liquid phase chemical hydrogen storage attracted considerable attention due to their high hydrogen content, high hydrogen purity, and easy control of the hydrogen generation rate [5,6]. Compared with other chemical hydrogen storage materials (such as hydrazine hydrate, ammonia borane and formic acid), potassium/sodium borohydride (KBH4/NaBH4) is more competitive because of several advantages, including safe production process, convenience of transportation, and environmentally benign hydrolysis product NaBO2. However, the rate of hydrogen generation from hydrolysis of KBH4/NaBH4 aqueous solution is usually low at elevated pH, especially under alkaline conditions, such as pH = 12 [7,8,9]. Therefore, catalysts are important for hydrolysis of KBH4, as shown in formula (1):
KBH 4 + 2 H 2 O Catalyst KBO 2 + 4 H 2
It is well-known that nanoparticles (NPs), especially noble metal NPs, can act as high-efficiency catalysts for hydrogen generation from hydrolysis of KBH4/NaBH4. Moreover, combinations of non-noble metal can reduce the use of noble metals and lower the cost of catalysts. Further, it can also improve the catalytic activities of the catalysts due to the synergistic effect between different metal atoms [9,10,11,12,13,14,15,16,17,18,19]. Our previous work has indicated that alloy-structured Au50Ni50 bimetallic nanoparticles (BNPs) exhibited catalytic activities several times higher for hydrogen generation from hydrolysis of NaBH4 aqueous solution, compared with that of Au and Ni monometallic nanoparticles (MNPs) [12]. Au/Co BNPs also displayed a much higher catalytic activity for hydrogen generation than that of Au and Co MNPs [13].
Rh NPs have attracted considerable attention in the catalysis area because they are active for many chemical reactions [20]. For example, Rh NPs supported on silica-coated magnetite showed significant hydrogenation activity of benzene and cyclohexene, and the catalytic activity remained unchangeable for up to 20 cycles [21]. Poly(N-vinyl-2-pyrrolidone)-protected Ru/Rh BNPs can act as highly efficient catalysts in the hydrolysis of ammonia borane for hydrogen generation [22]. [email protected](RhNi-alloy) nanocomposites supported on NiAl-layered double hydroxides (NiAl-LDHs) were reported to be highly efficient catalysts towards hydrogen generation in the hydrolysis of N2H4BH3 [23]. The addition of Rh metals has greatly improved the catalytic activity of Co-based catalysts in the ethanol stream reforming reaction, indicating the second metal could fundamentally influence the properties of the catalyst [24,25]. Nevertheless, the high cost of Rh hinders its wide industrial application. Thus, a combination of non-noble metal with Rh is a promising strategy for the development of Rh-based catalyst for hydrogen generation [23,26].
In the present paper, a series of ISOBAM-104 (poly (isobutylene-alt-maleic anhydride) (C8H10O3)m(C8H16O3N2)i, designed as ISOBAM-104) protected Rh/Ni BNPs were prepared by a facile method, and the relationship between compositions and structures of the BNPs on their catalytic activities for hydrogen generation were also investigated. ISOBAM-104 is expected to protect the metal NPs from agglomeration because it has numerous of functional groups and can act as chelant. The apparent activation energy of Rh10Ni90 BNPs for hydrolysis of KBH4 aqueous solution was calculated by the Arrhenius method. Moreover, the correlation between catalytic activities of Rh/Ni BNPs and their electronic properties was established based on a density functional theory (DFT) calculation.

2. Results and Discussion

2.1. Structure and Catalytic Activities of Rh/Ni Bimetallic Nanoparticles (BNPs)

UV-Vis spectra of as-prepared colloidal dispersion are shown in Figure 1. There is no surface plasmon resonance (SPR) peak of Rh, Ni MNPs or Rh/Ni BNPs in measuring range, which is consistent with previous reports [9,18]. The spectra of aqueous dispersed Rh/Ni BNPs displays featureless absorbance that monotonically increase toward a higher Rh content. The absorbance spectra of all BNPs lie between the spectrum of Rh and Ni MNPs, and the obvious differences in absorbance between as-prepared BNPs with varied Rh content suggest that alloy-structured Rh/Ni BNPs were formed.
Figure 2 presents a set of TEM micrographs of the prepared Rh, Ni MNPs and Rh/Ni BNPs. The individual NPs appear to be separated uniformly without obvious agglomeration. The average particle sizes of Rh, Rh90Ni10, Rh70Ni30, Rh30Ni70, Rh10Ni90 and Ni NPs based on size distribution analysis are about 1.9 ± 0.9 nm, 3.5 ± 1.9 nm, 3.7 ± 1.9 nm, 2.7 ± 0.8 nm, 2.7 ± 0.9 nm and 3.5 ± 1.2 nm, respectively. The elemental ratio of Rh70Ni30 BNPs at the selected square in Figure 3 was measured by mapping energy dispersion X-ray spectroscopy (EDS), and it indicates that the compositions of as-prepared Rh70Ni30 BNPs are similar to their feeding ratio.
In order to further verify the formation of an alloyed structure in the as-prepared BNPs, a lattice fringes analysis was also carried out, based on HRTEM images of the Rh70Ni30 colloidal dispersions. The particles exhibit an obvious crystalline structure, as revealed in Figure 4. The interplanar distances of three individual randomly-chosen particles of Rh70Ni30 BNPs were respectively measured to be 0.212 nm (particle-1), 0.218 nm (particle-2), and 0.216 nm (particle-3), as labeled in Figure 4. Comparing the results of Figure 4 with the theoretically interplanar spacing of Rh and Ni (based on XRD standard card, as shown in Table 1), the formation of individual Rh and Ni MNPs in the as-prepared samples can be ruled out. This is due to the mismatch of interplanar distances between these BNPs and Rh, or Ni MNPs. However, it should be noted that the measured interplanar distances lie between the interplanar spacing of Rh (111) (0.2196 nm), and that of Ni (111) (0.2034 nm), as shown in Table 2. This suggests that alloyed structures are formed in the particles and the interplanar spacing can be assigned to (111) of the alloy-structured Rh/Ni BNPs. To the best of our knowledge, this is the first report on the preparation of ISOBAM-104 protected alloy-structured Rh/Ni BNPs by using such a facile co-reduction method.
Catalytic activities of ISOBAM-104 protected RhxNi(100–x) (x = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100) NPs for H2 generation from hydrolysis of alkaline KBH4 aqueous solution at 303 K, are illustrated in Figure 5. The activities of BNPs were normalized to mol-H2·h−1·mol-Rh−1 since the catalytic activity of Ni MNPs is very low, showing that most of the Rh/Ni BNPs exhibit higher catalytic activities than that of Rh or Ni MNPs. Moreover, Rh10Ni90 BNPs possess the highest catalytic activities with a value of 11,580 mol-H2·h−1·mol-Rh−1 for hydrogen generation, which is respectively about 3 and 37 times higher than that of Rh (3560 mol-H2·h−1·mol-Rh−1), and Ni MNPs (310 mol-H2·h−1·mol-Ni−1).

2.2. Kinetic Study on Rh10Ni90 BNPs

The effects of pH and reaction temperature on the catalytic activities of the as-prepared BNPs were also investigated using Rh10Ni90 as model catalysts. It shows that the final hydrogen productivity of the BNPs decreases from 80% to 45%, with pH increasing from 12 to 14, as shown in Figure 6.
The apparent activation energy (Ea) of the BNPs for hydrogen generation from the hydrolysis of alkaline KBH4 solution was calculated by using the Arrhenius method [9,17,27]. The catalytic activities of Rh10Ni90 were enhanced with the increasing reaction temperature and a linear dependence between catalytic rates (in a logarithmic scale, ln k) and the reciprocals of temperature was observed (as shown in Figure 7). According to the Arrhenius equation, the slope of the linear plot is −Ea/R, where R represents the universal gas constant. Within the temperatures ranging from 303 to 323 K, Ea was calculated to be 47.2 ± 2.1 kJ/mol for Rh10Ni90 BNPs. These results suggest that the as-prepared Rh10Ni90 BNPs are excellent catalysts for the hydrolysis of KBH4 because of their lower apparent activation energy compared with other reported catalysts, such as 51.2 kJ/mol for Co-La-Zr-B NPs [28], 52.0 kJ/mol for Co-αAl2O3-Cu catalysts [29], 55.6 kJ/mol for Co/alginate hydrogels [30], and 48.8 kJ/mol for Mo incorporated Co-Ru-B catalysts [31], etc.

2.3. Correlation between Catalytic Activities of the Rh/Ni BNPs and Their Electronic Properties

Figure 5 showed that most of the as-prepared BNPs have higher activity than that of Rh and Ni MNPs, and that Rh10Ni90 BNPs possessed the highest catalytic activity for the hydrolysis of KBH4 among all prepared NPs. According to previous investigations [19,32,33,34], it is reasonable to suggest that the element components and electronic properties of Rh and Ni atoms affect the catalytic activities of the prepared BNPs. To confirm the existence of electron donation between Rh atoms and Ni atoms, DFT calculations were carried out to study the electron transfer of the BNPs, and Rh6Ni49 BNP were calculated as a model—the calculation results show that there is indeed an electron charge transfer effect between Rh and Ni atoms. The electron transfers from Rh atoms to Ni atoms owing to the relatively higher electron negativity value of Rh (2.28) than that of Ni (1.91), leading to the presence of negatively-charged Rh atoms and positively-charged Ni atoms in the Rh6Ni49 BNPs (Figure 8). It is believed that the charged Rh and Ni atoms can act as catalytically active sites, and can then enhance the catalytic activities for the hydrogen generation from hydrolysis of KBH4 aqueous solution [35,36,37,38].

3. Experiments

3.1. Raw Materials

Nickel chloride (NiCl2·6H2O, 99.0%, Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), rhodium chloride (RhCl3, 99.9%, Aladdin, Shanghai, China), potassium borohydride (KBH4, 96.0%, Aladdin, Shanghai, China), and potassium hydroxide (KOH, 96.0%, Aladdin, Shanghai, China) were directly used as raw materials without further purification. ISOBAM–104 (CAS NO. 52032-17-4, chemical structure is shown in Figure 9) was purchased from KURARAY company, Japan. Water was purified by a water distiller system.

3.2. Experiments

A series of Rh(100–x)Nix (x = 0, 10, 20, 30, 60, 80, 90, 95 and 100) BNPs were synthesized by changing the addition content of RhCl3 and NiCl2 with the total metal concentration kept at 0.66 mM. Rh/Ni BNPs were prepared through co-reduction method under 273 K in N2 atmosphere. For example, Rh50Ni50 BNPs were prepared as follows: 25 mL RhCl3 solution (0.66 mM) and 25 mL NiCl2 solution (0.66 mM) were firstly mixed homogeneously in a two-neck flask under vigorous stirring, and then 50 mL ISOBAM-104 (66 mM) was added into the flask and stirred for another 30 min. Then 10 mL KBH4 (16.5 mM) was injected into the aqueous solution within 5 s in an ice-water bath [39,40,41]. The color of the mixed solution slowly changed from transparent to black, which represents the formation of the Rh/Ni BNPs. Finally, colloidal dispersions Rh50Ni50 BNPs were obtained after another 1 h of mixing.

3.3. Characterization of Nanoparticles

UV-Vis absorption spectra were measured at 200–800 nm by a Shimadzu UV-2550 (Shimadzu company, Kobe, Japan) recording spectrophotometer. TEM images were taken with a FEI Tecnai G2 50-S-TWIN TEM (FEI company, Hillsboro, OR, USA) at the accelerated voltage of 80 kV. The specimens were prepared by placing two or three drops of the prepared colloidal aqueous solution onto a copper microgrid, which was covered with a thin amorphous carbon film, and drying it in air at an ambient temperature. Generally, to evaluate the mean diameter, at least 200 particles from different locations on the grid were selected for each sample. HRTEM images were observed at the accelerated voltage of 200 kV using a JEM-2100F (JEOL company, Tokyo, Japan) Field Emission High-resolution TEM. The EDS measurement was performed with a NORAN UTW type Si (Li) semiconducting detector attached to the HRTEM equipment.

3.4. Catalytic Properties

The catalytic performance of Rh/Ni BNPs was evaluated by the hydrogen generation from hydrolysis of alkaline KBH4 aqueous solution. The reaction was started when the alkaline KBH4 aqueous solution was added into the colloidal catalyst under continuous stirring. Hydrogen was bubbled through the suspension, and its volume was obtained with a water drainage method. At the same time, plots of hydrogen volume vs. reaction time with an interval of 2 s were collected by a computer. The turnover frequency (TOF) was calculated through the slope of a fitted straight line using H2 volume vs. reaction time curve. The initial specific activities (mol-H2·h−1·mol-Rh−1) related to the noble metal content of the catalysts were calculated for comparison. Every experiment was repeated at least twice, and the mean value of the measuring results was used for calculating the value of TOF. The catalytic kinetics were investigated at varied pH (12, 13 and 14, 303 K) and different temperatures (303 K, 308 K, 313 K, 318 K and 323 K, pH = 12,), using Rh10Ni90 as model catalysts.

3.5. DFT Calculation

DFT calculations were carried out using spin-polarization DFT/GGA with the PBE exchange-correlation functional [42], as implemented in the DMol3 package [43] (BIOVIA company, San Diego, CA, USA). Double numerical basis set and polarization functions were carried out to describe the valence electrons, and an electron relativistic core treatment was used to perform full optimization of the investigated cluster model of Rh6Ni49 BNP without symmetry constraint. The convergence criteria were set to medium quality with a tolerance for self-consistent field (SCF), optimization energy, maximum force, and maximum displacement of 105 Ha, 2 × 105 Ha, 0.004 Ha/Å and 0.005 Å, respectively. Charge analysis was performed on the basis of the Mulliken population distribution scheme [44,45].

4. Conclusions

ISOBAM-104 protected alloy-structured Rh/Ni BNPs were prepared by a co-reduction method and characterized by UV-Vis, TEM, EDS and HRTEM. The catalytic activities and kinetic study for KBH4 hydrolysis reaction were also investigated. The as-prepared Rh/Ni BNPs possessed high catalytic activities, and the activities of the Rh10Ni90 BNPs with an average size of 3 nm were higher than that of Ni MNPs. They were also higher than that of the Rh MNPs, even though the latter has a much smaller size of 1.9 nm. The apparent activation energy was calculated to be 47.2 ± 2.1 kJ/mol for Rh10Ni90 BNPs, which is lower than that of most reported catalysts, suggesting that Rh/Ni BNPs with low Rh loading were excellent catalysts for the hydrolysis of KBH4. The high catalytic activities of Rh/Ni BNPs could be attributed to the existence of the electron transfer effects between Rh and Ni atoms of the BNPs, which was confirmed by the DFT calculation. The enhanced performance of Rh/Ni BNPs is of major importance towards the direct production of H2 through hydrolysis of KBH4.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (Grant No. 5142184 and 51672194), and Program for Innovative Teams of Outstanding Young and Middle–aged Researchers in the Higher Education Institutions of Hubei Province (T201602).

Author Contributions

Haijun Zhang conceived and designed the experiment. Liqiong Wang, Chengpeng Jiao performed catalysts synthesis, whereas Zili Huang, Feng Liang, Simin Liu and Yuhua Wang carried out catalyst characterization and evaluation. Liqiong Wang, Liang Huang and Haijun Zhang contributed with the analysis and interpretation of characterization results. All authors discussed the results and approved the final version of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Chu, D.M.; Zhang, C.Y.; Yang, P.; Du, Y.K.; Lu, C. WS2 as an effective noble-Metal free cocatalyst modified TiSi2 for enhanced photocatalytic hydrogen evolution under visible light irradiation. Catalysts 2016, 6, 136. [Google Scholar] [CrossRef]
  2. Konsolakis, M.; Ioakimidis, Z.; Kraia, T.; Marnellos, G.E. Hydrogen production by ethanol steam reforming (ESR) over CeO2 supported transition metal (Fe, Co, Ni, Cu) catalysts: Insight into the structure-Activities relationship. Catalysts 2016, 6, 39. [Google Scholar] [CrossRef]
  3. Zhang, F.C.; Chen, R.; Zhang, W.H.; Zhang, W.B. A Ti-Decorated boron monolayer: A promising material for hydrogen storage. RSC Adv. 2016, 6, 12925–12931. [Google Scholar] [CrossRef]
  4. Wang, L.; Zhang, T.; He, H.Q.; Zhang, J.L. Mechanism for H2 release from potential hydrogen storage materials of phosphine alane and phosphine borane in the presence or absence of alane or borane: A theoretical study. RSC Adv. 2013, 3, 21949–21958. [Google Scholar] [CrossRef]
  5. Yadav, M.; Xu, Q. Liquid-phase chemical hydrogen storage materials. Energy Environ. Sci. 2012, 5, 9698–9725. [Google Scholar] [CrossRef]
  6. Jiang, H.L.; Singh, S.K.; Yan, J.M.; Zhang, X.B.; Xu, Q. Liquid-phase chemical hydrogen storage: Catalytic hydrogen generation under ambient conditions. ChemSusChem 2010, 3, 541–549. [Google Scholar] [CrossRef] [PubMed]
  7. Wang, S.B.; Xin, X.; Zhang, H.; Shen, J.L.; Zheng, Y.; Song, Z.H.; Yang, Y.Z. Stable monodisperse colloidal spherical gold nanoparticles formed by an imidazolium gemini surfactant-based water-in-oil microemulsion with excellent catalytic performance. RSC Adv. 2016, 6, 28156–28164. [Google Scholar] [CrossRef]
  8. Jia, H.; Gao, X.P.; Chen, Z.L.; Liu, G.Q.; Zhang, X.; Yan, H.; Zhou, H.T.; Zheng, L.Q. The high yield synthesis and characterization of gold nanoparticles with superior stability and their catalytic activities. Cryst. Eng. Commun. 2012, 14, 7600–7606. [Google Scholar] [CrossRef]
  9. Jiao, C.P.; Huang, Z.L.; Wang, X.F.; Zhang, H.J.; Lu, L.L.; Zhang, S.W. Synthesis of Ni/Au/Co trimetallic nanoparticles and their catalytic activities for hydrogen generation from alkaline sodium borohydride aqueous solution. RSC Adv. 2015, 5, 34364–34371. [Google Scholar] [CrossRef]
  10. Seven, F.; Sahiner, N. Enhanced catalytic performance in hydrogen generation from NaBH4 hydrolysis by super porous cryogel supported Co and Ni catalysts. J. Power Sources 2014, 272, 128–136. [Google Scholar] [CrossRef]
  11. Wu, C.; Bai, Y.; Liu, D.X.; Wu, F.; Pang, M.L.; Yi, B.L. Ni–Co–B catalyst-promoted hydrogen generation by hydrolyzing NaBH4 solution for in situ hydrogen supply of portable fuel cells. Catal. Today 2011, 170, 33–39. [Google Scholar] [CrossRef]
  12. Wang, X.F.; Sun, S.R.; Huang, Z.L.; Zhang, H.J.; Zhang, S.W. Preparation and catalytic activities of PVP-protected Au/Ni bimetallic nanoparticles for hydrogen generation from hydrolysis of basic NaBH4 solution. Int. J. Hydrogen Energy 2014, 39, 905–916. [Google Scholar] [CrossRef]
  13. Wang, X.F.; Huang, Z.L.; Lu, L.L.; Zhang, H.J.; Cao, Y.N.; Gu, Y.J.; Cheng, Z.; Zhang, S.W. Preparation and Catalytic Activities of Au/Co Bimetallic Nanoparticles for Hydrogen Generation from NaBH4 Solution. J. Nanosci. Nanotechnol. 2015, 15, 2770–2776. [Google Scholar] [CrossRef] [PubMed]
  14. Yang, X.J.; Cheng, F.Y.; Liang, J.; Tao, Z.L.; Chen, J. PtxNi1–x nanoparticles as catalysts for hydrogen generation from hydrolysis of ammonia borane. Int. J. Hydrogen Energy 2009, 34, 8785–8791. [Google Scholar] [CrossRef]
  15. Wang, H.L.; Yan, J.M.; Wang, Z.L; Jiang, Q. One-step synthesis of [email protected] core-shell nanoparticles: Highly active catalyst for hydrolytic dehydrogenation of ammonia borane. Int. J. Hydrogen Energy 2012, 37, 10229–10235. [Google Scholar] [CrossRef]
  16. Pan, Y.; Zhang, F.; Wu, K.; Lu, Z.Y.; Chen, Y.; Zhou, Y.M.; Tang, Y.W.; Lu, T.H. Carbon supported Palladium-Iron nanoparticles with uniform alloy structure as methanol-tolerant electrocatalyst for oxygen reduction reaction. Int. J. Hydrogen Energy 2012, 37, 2993–3000. [Google Scholar] [CrossRef]
  17. Zhang, H.J.; Deng, X.G.; Jiao, C.P.; Lu, L.L.; Zhang, S.W. Preparation and catalytic activities for H2O2 decomposition of Rh/Au bimetallic nanoparticles. Mater. Res. Bull. 2016, 79, 29–35. [Google Scholar] [CrossRef]
  18. Zhang, H.J.; Cao, Y.N.; Lu, L.L.; Cheng, Z.; Zhang, S.W. Trimetallic Au/Pt/Rh nanoparticles as highly active catalysts for aerobic glucose oxidation. Metall. Mater. Trans. B 2014, 46, 523–530. [Google Scholar] [CrossRef]
  19. Zhang, H.J.; Watanabe, T.; Okumura, M.; Haruta, M.; Toshima, N. Catalytically highly active top gold atom on palladium nanocluster. Nat. Mater. 2012, 11, 49–52. [Google Scholar] [CrossRef] [PubMed]
  20. Larichev, Y.V.; Netskina, O.V.; Komova, O.V.; Simagina, V.I. Comparative XPS study of Rh/Al2O3 and Rh/TiO2 as catalysts for NaBH4 hydrolysis. Int. J. Hydrogen Energy 2010, 35, 6501–6507. [Google Scholar] [CrossRef]
  21. Jacinto, M.J.; Kiyohara, P.K.; Masunaga, S.H.; Jardim, R.F.; Rossi, L.M. Recoverable rhodium nanoparticles: Synthesis, characterization and catalytic performance in hydrogenation reactions. Appl. Catal. A Gen. 2008, 338, 52–57. [Google Scholar] [CrossRef]
  22. Rakap, M. PVP-stabilized Ru-Rh nanoparticles as highly efficient catalysts for hydrogen generation from hydrolysis of ammonia borane. J. Alloys Compd. 2015, 649, 1025–1030. [Google Scholar] [CrossRef]
  23. Li, C.M.; Dou, Y.B.; Liu, J.; Chen, Y.D.; He, S.; Wei, M.; Evans, D.G.; Duan, X. Synthesis of supported [email protected](RhNi-alloy) nanocomposites as an efficient catalyst towards hydrogen generation from N2H4BH3. Chem. Commun. 2013, 49, 9992–9994. [Google Scholar] [CrossRef] [PubMed]
  24. Ferencz, Z.; Erdőhelyi, A.; Baán, K.; Oszkó, A.; Óvári, L.; Kónya, Z.; Papp, C.; Steinrück, H.P.; Kiss., J. Effects of support and Rh additive on Co-based catalysts in the ethanol steam reforming reaction. ACS Catal. 2014, 4, 1205–1218. [Google Scholar] [CrossRef]
  25. Varga, E.; Baán, K.; Samu, G.F.; Erdőhelyi, A.; Oszkó, A.; Kónya, Z.; Kiss, J. The Effect of Rh on the Interaction of Co with Al2O3 and CeO2 Supports. Catal. Lett. 2016, 146, 1800–1807. [Google Scholar] [CrossRef]
  26. Arbag, H.; Yasyerli, S.; Yasyerli, N.; Dogu, G. Activities and stability enhancement of Ni-MCM-41 catalysts by Rh incorporation for hydrogen from dry reforming of methane. Int. J. Hydrogen Energy 2010, 35, 2296–2304. [Google Scholar] [CrossRef]
  27. Zhang, H.J.; Li, W.Q.; Gu, Y.J.; Zhang, S.W. Preparation and Catalytic Activities of Poly(N-vinyl-2-pyrrolidone)-Protected Au nanoparticles for the aerobic oxidation of glucose. J. Nanosci. Nanotechnol. 2014, 14, 5743–5751. [Google Scholar] [CrossRef] [PubMed]
  28. Loghmani, M.H.; Shojaei, A.F. Hydrogen production through hydrolysis of sodium borohydride: Oleic acid stabilized Co–La–Zr–B nanoparticle as a novel catalyst. Energy 2014, 68, 152–159. [Google Scholar] [CrossRef]
  29. Chamoun, R.; Demirci, U.B.; Zaatar, Y.; Khoury, A.; Miele, P. Co–αAl2O3–Cu as shaped catalyst in NaBH4 hydrolysis. Int. J. Hydrogen Energy 2010, 35, 6583–6591. [Google Scholar] [CrossRef]
  30. Ai, L.H.; Gao, X.Y.; Jiang, J. In situ synthesis of cobalt stabilized on macroscopic biopolymer hydrogel as economical and recyclable catalyst for hydrogen generation from sodium borohydride hydrolysis. J. Power Sources 2014, 257, 213–220. [Google Scholar] [CrossRef]
  31. Wang, W.L.; Zhao, Y.C.; Chen, D.H.; Wang, X.; Peng, X.L.; Tian, J.N. Promoted Mo incorporated Co-Ru-B catalyst for fast hydrolysis of NaBH4 in alkaline solutions. Int. J. Hydrogen Energy 2014, 39, 16202–16211. [Google Scholar] [CrossRef]
  32. Zhang, H.J.; Lu, L.L.; Kawashima, K.; Okumura, M.; Haruta, M.; Toshima, N. Synthesis and catalytic activities of crown jewel-structured (IrPd)/Au trimetallic nanoclusters. Adv. Mater. 2015, 27, 1383–1388. [Google Scholar] [CrossRef] [PubMed]
  33. Zhang, H.J.; Toshima, N. Synthesis of Au/Pt bimetallic nanoparticles with a Pt-rich shell and their high catalytic activities for aerobic glucose oxidation. J. Colloid Interface Sci. 2013, 394, 166–176. [Google Scholar] [CrossRef] [PubMed]
  34. Zhang, H.J.; Okumura, M.; Toshima, N. Stable Dispersions of PVP-protected Au/Pt/Ag trimetallic nanoparticles as highly active colloidal catalysts for aerobic glucose oxidation. J. Phys. Chem. C 2011, 115, 14883–14891. [Google Scholar] [CrossRef]
  35. Zhang, H.J.; Toshima, N. Crown Jewel-structured Au/Pd nanoclusters as novel catalysts for aerobic glucose oxidation. J. Nanosci. Nanotechnol. 2013, 13, 5405–5412. [Google Scholar] [CrossRef] [PubMed]
  36. Zhang, H.J.; Watanabe, T.; Okumura, M.; Haruta, M.; Toshima, N. Crown Jewel catalyst: How neighboring atoms affect the catalytic activities of top Au atoms? J. Catal. 2013, 305, 7–18. [Google Scholar] [CrossRef]
  37. Zhang, H.J.; Kawashima, K.; Okumura, M.; Toshima, N. Colloidal Au single-atom catalysts embedded on Pd nanoclusters. J. Mater. Chem. A 2014, 2, 13498–13508. [Google Scholar] [CrossRef]
  38. Zhang, H.J.; Wang, L.Q.; Lu, L.L.; Toshima, N. Preparation and catalytic activities for aerobic glucose oxidation of Crown Jewel structured Pt/Au bimetallic nanoclusters. Sci. Rep. 2016, 6, 30752–30762. [Google Scholar] [CrossRef] [PubMed]
  39. Zhang, H.J.; Haba, M.; Okumura, M.; Akita, T.; Hashimoto, S.; Toshima, N. Novel formation of Ag/Au bimetallic nanoparticles by physical mixture of monometallic nanoparticles in dispersions and their application to catalysts for aerobic glucose oxidation. Langmuir 2013, 29, 10330–10339. [Google Scholar] [CrossRef] [PubMed]
  40. Zhang, H.J.; Toshima, N. Fabrication of catalytically active AgAu bimetallic nanoparticles by physical mixture of small Au clusters with Ag ions. Appl. Catal. A 2012, 447–448, 81–88. [Google Scholar] [CrossRef]
  41. Zhang, H.J.; Toshima, N. Preparation of novel Au/Pt/Ag trimetallic nanoparticles and their high catalytic activities for aerobic glucose oxidation. Appl. Catal. A 2011, 400, 9–13. [Google Scholar] [CrossRef]
  42. Brajczewska, M.; Vieira, A.; Fiolhais, C.; Perdew, J.P. Volume shift and charge instability of simple-metal clusters. Prog. Surf. Sci. 1996, 53, 305–313. [Google Scholar] [CrossRef]
  43. Delley, B. DMol3 DFT studies: From molecules and molecular environments to surfaces and solids. Comput. Mater. Sci. 2000, 17, 122–126. [Google Scholar] [CrossRef]
  44. Reed, A.E.; Weinstock, R.B.; Weinhold, F. Natural population analysis. J. Chem. Phys. 1985, 83, 735–746. [Google Scholar] [CrossRef]
  45. Clark, A.E.; Sonnenberg, J.L.; Hay, P.J.; Martin, R.L. Density and wave function analysis of actinide complexes: What can fuzzy atom, atoms-in-molecules, Mulliken, Löwdin, and natural population analysis tell us? J. Chem. Phys. 2004, 121, 2563–2570. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Ultraviolet-visible spectrophotometry (UV-Vis) spectra of colloidal dispersions of Rh(100–x) Nix nanoparticles (NPs) (x = 0, 10, 20, 30, 60, 80, 90 and 100) (RISO = 40, RISO presents the molar ratio of ISOBAM-104 in alkaline solution to the total metals in the colloidal catalyst mixture; CMetal = 0.66 mM, reduced under ice-water bath for 1 h.).
Figure 1. Ultraviolet-visible spectrophotometry (UV-Vis) spectra of colloidal dispersions of Rh(100–x) Nix nanoparticles (NPs) (x = 0, 10, 20, 30, 60, 80, 90 and 100) (RISO = 40, RISO presents the molar ratio of ISOBAM-104 in alkaline solution to the total metals in the colloidal catalyst mixture; CMetal = 0.66 mM, reduced under ice-water bath for 1 h.).
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Figure 2. Transmission electron microscopy (TEM) images and size distribution histograms of colloidal dispersions of Rh(100–x)Nix (x = 0, 10, 30, 70, 90 and 100) NPs (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h).
Figure 2. Transmission electron microscopy (TEM) images and size distribution histograms of colloidal dispersions of Rh(100–x)Nix (x = 0, 10, 30, 70, 90 and 100) NPs (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h).
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Figure 3. TEM image (a) and mapping-EDS (b) of Rh70Ni30 BNPs (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h).
Figure 3. TEM image (a) and mapping-EDS (b) of Rh70Ni30 BNPs (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h).
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Figure 4. High-resolution transmission electron microscopy (HRTEM) image of as-prepared Rh70Ni30 BNPs (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h).
Figure 4. High-resolution transmission electron microscopy (HRTEM) image of as-prepared Rh70Ni30 BNPs (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h).
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Figure 5. Comparison of catalytic activities of Rh(100–x) Nix BNPs with Rh and Ni MNPs (x = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100) and NPs (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h; pH = 12 for H2 generation, 30 °C. The activities of Ni MNPs were normalized to mol-H2·h−1·mol-Ni−1).
Figure 5. Comparison of catalytic activities of Rh(100–x) Nix BNPs with Rh and Ni MNPs (x = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100) and NPs (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h; pH = 12 for H2 generation, 30 °C. The activities of Ni MNPs were normalized to mol-H2·h−1·mol-Ni−1).
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Figure 6. Evaluation of H2 productivity with reaction time of Rh10Ni90 BNPs at different pH values (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h; 30 °C).
Figure 6. Evaluation of H2 productivity with reaction time of Rh10Ni90 BNPs at different pH values (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h; 30 °C).
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Figure 7. Linear fit of lnk to 1/T of Rh10Ni90 catalyst for hydrogen generation from KBH4 (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h; pH = 12 for H2 generation, 30 °C).
Figure 7. Linear fit of lnk to 1/T of Rh10Ni90 catalyst for hydrogen generation from KBH4 (RISO = 40, CMetal = 0.66 mM, reduced under ice-water bath for 1 h; pH = 12 for H2 generation, 30 °C).
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Figure 8. The density functional theory (DFT) calculated Mulliken charge on selected Rh atom and Ni atoms (green, Rh; and purple, Ni).
Figure 8. The density functional theory (DFT) calculated Mulliken charge on selected Rh atom and Ni atoms (green, Rh; and purple, Ni).
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Figure 9. The chemical structure of ISOBAM-104.
Figure 9. The chemical structure of ISOBAM-104.
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Table 1. Lattice spacing (nm) and indexed reflection planes of Rh and Ni.
Table 1. Lattice spacing (nm) and indexed reflection planes of Rh and Ni.
Interplanar Face(111)(200)(220)(311)(222)(400)
Element
Rh (ICCD 00-005-0685)0.21960.19020.13450.11470.10980.0951
Ni (ICCD 00-004-0850)0.20340.17620.12460.10620.10170.0881
Table 2. Lattice spacing (nm) and indexed reflection planes of Rh70Ni30 BNPs determined by HRTEM in Figure 4.
Table 2. Lattice spacing (nm) and indexed reflection planes of Rh70Ni30 BNPs determined by HRTEM in Figure 4.
ParticlesMeasured Lattice Spacing of BNPsComparison of Lattice Spacing of Rh/Ni BNPs with Rh and Ni MNPsIndexed Reflection Planes of Rh/Ni BNPs
10.212Between Rh(111) and Ni(111), 0.2196 > 0.212 > 0.2034(111)
20.218Between Rh(111) and Ni(111), 0.2196 > 0.218 > 0.2034(111)
30.216Between Rh(111) and Ni(111), 0.2196 > 0.216 > 0.2034(111)

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