Qilu Yao

One-pot synthesis of core-shell Cu@SiO2 nanospheres and their catalysis for hydrolytic dehydrogenation of ammonia borane and hydrazine borane.

Ultrafine copper nanoparticles (Cu NPs) within porous silica nanospheres (Cu@SiO2) were prepared via a simple one-pot synthetic route in a reverse micelle system and characterized by SEM, TEM, EDX, XRD, N2 adsorption-desorption, CO-TPD, XPS, and ICP methods. The characterized results show that ultrafine Cu NPs with diameter of around 2 nm are effectively embedded in the center of well-proportioned spherical SiO2 NPs of about 25 nm in diameter. Compared to commercial SiO2 supported Cu NPs, SiO2 nanospheres supported Cu NPs, and free Cu NPs, the synthesized core-shell nanospheres Cu@SiO2 exhibit a superior catalytic activity for the hydrolytic dehydrogenation of ammonia borane (AB, NH3BH3) and hydrazine borane (HB, N2H4BH3) under ambient atmosphere at room temperature. The turnover frequencies (TOF) for the hydrolysis of AB and HB in the presence of Cu@SiO2 nanospheres were measured to be 3.24 and 7.58 mol H2 (mol Cu min)−1, respectively, relatively high values for Cu nanocatalysts in the same reaction. In addition, the recycle tests show that the Cu@SiO2 nanospheres are still highly active in the hydrolysis of AB and HB, preserving 90 and 85% of their initial catalytic activity even after ten recycles, respectively.

High Pt-like activity of the Ni–Mo/graphene catalyst for hydrogen evolution from hydrolysis of ammonia borane

Ni nanoparticles modified with a Mo dopant have been synthesized on graphene sheets via a facile chemical reduction route, which show the highest catalytic activity reported to date for noble-metal-free catalysts for hydrogen evolution from the hydrolysis of ammonia borane with a turnover frequency value as high as 66.7 mol H2 (mol metal min)−1.

CeOx-modified RhNi nanoparticles grown on rGO as highly efficient catalysts for complete hydrogen generation from hydrazine borane and hydrazine

CeOx-modified RhNi nanoparticles (NPs) grown on reduced graphene oxide (rGO) (RhNi@CeOx/rGO) have been facilely prepared and successfully used as highly efficient catalysts for the rapid and complete hydrogen generation from aqueous solution of hydrazine borane (N2H4BH3) and hydrazine (N2H4), respectively. It was found that the CeOx-doped RhNi NPs with a size of around 3.5 nm were highly dispersed on rGO nanosheets. Among all the catalysts investigated, the optimized catalyst Rh0.8Ni0.2@CeOx/rGO with a CeOx content of 13.9 mol% exhibited the highest catalytic performance. The total turnover frequency (TOF) of Rh0.8Ni0.2@CeOx/rGO for hydrogen generation from N2H4BH3 reached 666.7 h−1 (molH2 mol(Rh+Ni)−1 h−1) at 323 K, which was among the highest of all the catalysts reported to date for this reaction, 10-fold higher than that of the benchmark catalyst Rh0.8Ni0.2, and 3-fold higher than that of Rh0.8Ni0.2 with a CeOx dopant (Rh0.8Ni0.2@CeOx) and a rGO support (Rh0.8Ni0.2/rGO). Even at room temperature, Rh0.8Ni0.2@CeOx/rGO can achieve a complete hydrogen generation from N2H4BH3 and N2H4 with a TOF value of 111.2 and 36.4 h−1. This excellent catalytic performance might be attributed to the synergistic structural and electronic effects of the RhNi NPs, CeOx dopant, and rGO support. Moreover, this general method can be easily extended to facile synthesis of other metal/rGO systems with the doping of rare-earth oxides for more applications.

Ruthenium nanoparticles confined in SBA-15 as highly efficient catalyst for hydrolytic dehydrogenation of ammonia borane and hydrazine borane

Ultrafine ruthenium nanoparticles (NPs) within the mesopores of the SBA-15 have been successfully prepared by using a “double solvents” method, in which n-hexane is used as a hydrophobic solvent and RuCl3 aqueous solution is used as a hydrophilic solvent. After the impregnation and reduction processes, the samples were characterized by XRD, TEM, EDX, XPS, N2 adsorption-desorption, and ICP techniques. The TEM images show that small sized Ru NPs with an average size of 3.0 ± 0.8 nm are uniformly dispersed in the mesopores of SBA-15. The as-synthesized Ru@SBA-15 nanocomposites (NCs) display exceptional catalytic activity for hydrogen generation by the hydrolysis of ammonia borane (NH3BH3, AB) and hydrazine borane (N2H4BH3, HB) at room temperature with the turnover frequency (TOF) value of 316 and 706 mol H2 (mol Ru min)−1, respectively, relatively high values reported so far for the same reaction. The activation energies (Ea) for the hydrolysis of AB and HB catalyzed by Ru@SBA-15 NCs are measured to be 34.8 ± 2 and 41.3 ± 2 kJ mol−1, respectively. Moreover, Ru@SBA-15 NCs also show satisfied durable stability for the hydrolytic dehydrogenation of AB and HB, respectively.

Nanocatalysts for hydrogen generation from ammonia borane and hydrazine borane

Ammonia borane (denoted as AB, NH3BH3) and hydrazine borane (denoted as HB, N2H4BH3), having hydrogen content as high as 19.6 wt% and 15.4 wt%, respectively, have been considered as promising hydrogen storage materials. Particularly, the AB and HB hydrolytic dehydrogenation system can ideally release 7.8 wt% and 12.2 wt% hydrogen of the starting materials, respectively, showing their high potential for chemical hydrogen storage. A variety of nanocatalysts have been prepared for catalytic dehydrogenation from aqueous or methanolic solution of AB and HB. In this review, we survey the research progresses in nanocatalysts for hydrogen generation from the hydrolysis or methanolysis of NH3BH3 and N2H4BH3.

Controlled Synthesis of MOF-Encapsulated NiPt Nanoparticles toward Efficient and Complete Hydrogen Evolution from Hydrazine Borane and Hydrazine

The catalytic dehydrogenation of hydrazine borane (N2H4BH3) and hydrous hydrazine (N2H4·H2O) for H2 evolution is considered as two of the pivotal reactions for the implementation of the hydrogen-based economy. A reduction rate controlled strategy is successfully applied for the encapsulating of uniform tiny NiPt alloy nanoclusters within the opening porous channels of MOFs in this work. The resultant Ni0.9Pt0.1/MOF core-shell composite with a low Pt content exerted exceedingly high activity and durability for complete H2 evolution (100% hydrogen selectivity) from alkaline N2H4BH3 and N2H4·H2O solution. The features of small NiPt alloy NPs, strong synergistic effect between NiPt alloy NPs and the MOF, and open pore structure for freely mass transfer made NiPt/MIL-101 an excellent catalyst for highly efficient H2 evolution from N2H4BH3 or N2H4·H2O.

Catalytic hydrolysis of ammonia borane by cobalt nickel nanoparticles supported on reduced graphene oxide for hydrogen generation

Well dispersed magnetically recyclable bimetallic CoNi nanoparticles (NPs) supported on the reduced graphene oxide (RGO) were synthesized by one-step in situ coreduction of aqueous solution of cobalt(II) chloride, nickel (II) chloride, and graphite oxide (GO) with ammonia borane (AB) as the reducing agent under ambient condition. The CoNi/RGO NPs exhibits excellent catalytic activity with a total turnover frequency (TOF) value of 19.54 mol H2 mol catalyst−1 min−1 and a low activation energy value of 39.89 kJ mol−1 at room temperature. Additionally, the RGO supported CoNi NPs exhibit much higher catalytic activity than the monometallic and RGO-free CoNi counterparts. Moreover, the as-prepared catalysts exert satisfying durable stability and magnetically recyclability for the hydrolytic dehydrogenation of AB, which make the practical reusing application of the catalysts more convenient. The usage of the low-cost, easy-getting catalyst to realize the production of hydrogen under mild condition gives more confidence for the application of ammonia borane as a hydrogen storage material. Hence, this general method indicates that AB can be used as both a potential hydrogen storage material and an efficient reducing agent, and can be easily extended to facile preparation of other RGO-based metallic systems.

Facile Synthesis of Platinum–Cerium(IV) Oxide Hybrids Arched on Reduced Graphene Oxide Catalyst in Reverse Micelles with High Activity and Durability for Hydrolysis of Ammonia Borane

Highly dispersed Pt-CeO2 hybrids arched on reduced graphene oxide (Pt-CeO2 /rGO) were facilely synthesized by a combination of the reverse micelle technique and a redox reaction without any additional reductant or surfactant. Under a N2 atmosphere, the redox reaction between Ce3+ and Pt2+ occurs automatically in alkaline solution, which results in the formation of Pt-CeO2 /rGO nanocomposites (NCs). The as-synthesized Pt-CeO2 /rGO NCs exhibit superior catalytic performance relative to that shown by the free Pt nanoparticles, Pt/rGO, Pt-CeO2 hybrid, and the physical mixture of Pt-CeO2 and rGO; furthermore, the nanocomposites show significantly better activity than the commercial Pt/C catalyst toward the hydrolysis of ammonia borane (NH3 BH3 ) at room temperature. Moreover, the Pt-CeO2 /rGO NCs have remarkable stability, and 92 % of their initial catalytic activity is preserved even after 10 runs. The excellent activity of the Pt-CeO2 /rGO NCs can be attributed not only to the synergistic structure but also to the electronic effects of the Pt-CeO2 /rGO NCs among Pt, CeO2 , and rGO.

Base-promoted hydrolytic dehydrogenation of ammonia borane catalyzed by noble-metal-free nanoparticles

Hydrogen is a potentially ideal alternative energy source for both environmental and economic reasons. The development of sustainable, efficient, and economical catalysts towards hydrogen generation from hydrogen storage materials (e.g., ammonia borane, AB) has been one of the active and challenging research areas. In this work, noble-metal-free CuCoMo nanoparticles (NPs) without any surfactant or support have been prepared via a facile co-reduction method at room temperature and used as highly efficient catalysts for hydrogen generation from an aqueous AB solution. Compared to their monometallic and bimetallic counterparts, the obtained trimetallic Cu0.72Co0.18Mo0.1 NPs exhibit the highest catalytic activity for the hydrolysis of AB with a total turnover frequency (TOF) value of 46.0 min−1 at room temperature under ambient atmosphere. The Cu0.72Co0.18Mo0.1 NPs only needed 0.63 min to completely hydrolyse AB in the presence of a basic solution (NaOH, 1 M) with a TOF value as high as 119.0 min−1 at room temperature, which is among the highest values of all the noble-metal-free catalysts ever reported for the same reaction, wherein NaOH plays an important role in improving the catalytic activity. In addition, it is found that the hydrogen generation rate can be improved by adding a base (e.g., NaOH, KOH, etc.) into the reaction solution, while the presence of NH4+ species (e.g., NH3·H2O, NH4Cl, etc.) is unfavorable for the hydrolysis of AB.

Metal–organic framework immobilized RhNi alloy nanoparticles for complete H2 evolution from hydrazine borane and hydrous hydrazine

Metal–organic framework (MOF) immobilized Rh–Ni alloy nanoparticles (NPs) with a mean size of 2.8 nm have been facilely and successfully fabricated via a reduction rate controlled method. Bimetallic NP/MOF composites with uniform tiny RhNi alloy NPs immobilized on MOFs, high surface areas (1970 m2 g−1), and accessible porous structure have been obtained. The resulting RhNi/MOF catalysts show high catalytic activity and robust durability for complete H2 evolution from hydrazine borane (N2H4BH3) and hydrous hydrazine (N2H4·H2O). The optimized Rh0.8Ni0.2/MIL-101 catalyst exhibits excellent catalytic performance for the dehydrogenation of N2H4BH3 and N2H4·H2O in aqueous solution with 100% conversion and hydrogen selectivity, high total turnover frequencies (TOF), up to 1200 and 428.6 mol(H2) mol(Rh+Ni)−1 h−1, respectively, the highest over Rh-based catalysts. The high activity and prominent durability of Rh0.8Ni0.2/MIL-101 are highly dependent on the features of the MOF immobilized tiny RhNi alloy NPs, the strong interaction between the MOF crystal and RhNi alloy NPs, the optimized surface and electronic structure of RhNi alloy with an atomic ratio of 8 : 2, and the accessible open porous structure for free mass transfer.