Xiangshu Chen

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.

Facile in situ synthesis of copper nanoparticles supported on reduced graphene oxide for hydrolytic dehydrogenation of ammonia borane

Reduced graphene oxide (RGO) supported copper nanoparticles (NPs) were synthesized via a facile in situ procedure using ammonia borane (AB) as a reductant. The as-prepared nanocatalysts exert satisfactory catalytic activity (3.61 mol H2 mol per catalyst per min), and appear to be the best Cu nanocatalysts up to now for the dehydrogenation of ammonia borane.

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.

Facile synthesis and enhanced visible-light photocatalytic activity of graphitic carbon nitride decorated with ultrafine Fe2O3 nanoparticles

Hybrid nanocomposites based on graphitic carbon nitride (g-C3N4) nanosheet supported ultrafine Fe2O3 nanoparticles have been successfully prepared by a facile thermal polymerization and deposition-precipitation method. Characterization results demonstrate that Fe2O3/g-C3N4 nanocomposites exhibit a well-defined morphology, in which Fe2O3 nanocrystals of 3 nm size with a narrow particle distribution are uniformly dispersed on the layers of the g-C3N4 nanosheets. Photocatalytic reaction results indicate that the photocatalytic activity of g-C3N4 is significantly enhanced after introduction of a small amount of Fe2O3, and the optimum activity of the Fe2O3/g-C3N4 nanocomposites with a weight ratio of Fe2O3 at 0.1% is up to about 3 times and 62 times higher than those of pure g-C3N4 and pure Fe2O3, respectively, for the degradation of organic dye Rhodamine B (RhB) under visible light irradiation. The high performance of the Fe2O3/g-C3N4 photocatalysts is mainly attributed to the synergistic effect at the interface of the heterojunction between Fe2O3 nanoparticles and g-C3N4 nanosheets, including improved separation efficiency of the charge carriers, a suppressed recombination process and suitable band position of the composites. These results underline the potential for the development of effective, low-cost and earth-abundant photocatalysts for the promotion of water splitting and environmental remediation under natural sunlight by construction of sustainable g-C3N4 polymeric materials.

SO3H-functionalized Brønsted acidic ionic liquids as efficient catalysts for the synthesis of isoamyl salicylate

Six Bronsted acidic ionic liquids (BAILs) composed of [HSO4] were prepared, characterized, and used as catalysts of low dosage in the synthesis of isoamyl salicylate. The effects of various parameters such as the kind of BAILs, temperature, catalyst loading, and molar ratio of the reactants on the conversion of salicylic acid were also examined in detail. The results suggested that the catalytic performances of BAILs were of close relevance to their Hammett acidities. The SO3H-functionalized BAILs 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate ([BSmim][HSO4]) and N-(4-sulfonic acid) butyl triethylammonium hydrogen sulfate ([BSEt3N][HSO4]) of strong acidities exhibited excellently catalytic activities and selectivities in the esterification of salicylic acid with isoamyl alcohol. The fully optimized geometries of [BSmim][HSO4] and [BSEt3N][HSO4] further manifest that their strong acidities are derived from the strong interactions between the anion with the sulfonic acid group. In addition, it was found that [BSmim][HSO4] could be also recovered easily and used repetitively at least six times without obvious decline in activity and quantity.

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.