Preparation Of Supported Ru-based Alloy Catalysts And Their Catalytic Performance For Generating Hydrogen From Hydrolysis Of Borohydrides

Global energy demand has grown rapidly in recent years,and this trend is expected to continue for a long time.Hydrogen energy is a kind of clean and renewable energy.Its low density and the harsh conditions of traditional hydrogen storage have limited its development.Borohydrides such as NH₃BH₃ and Na BH₄ are non-toxic and stable solid hydrogen storage materials with high hydrogen content.However,without the assistance of a suitable catalyst,it is impossible to generate hydrogen rapidly from hydrolysis of these borohydrides.The high purity hydrogen can be produced fast by adding suitable catalyst into aqueous solution of the borohydrides at normal temperature and pressure.Compared with other precious metals,Ru has a high catalytic activity and a relatively-low cost.This work is aimed at preparing ruthenium-based alloy catalysts with excellent catalytic performance and good stability,and the catalysts is expected to find its significant use in the hydrolysis of borohydrides to generate hydrogen.Ru Fe/N-C catalyst was prepared using an impregnation co-reduction way,by which Ru Fe alloy nanoparticles were anchored on the surface of spherical nitrogen-doped carbon support.This carbon support was obtained from resorcinol-formaldehyde resin.The structure and micro-morphology of the catalyst were studied by using powder X-ray diffraction technique,laser Raman spectroscopy,N₂absorption-desorption technique,high-resolution transmission electron microscope,scanning electron microscope,and X-ray photoelectron spectroscopy.The results indicated that doping nitrogen atoms in the carbon material changed the electronic structure of the carbon matrix and improved the dispersibility of the metal nanoparticles.The catalytic performance of supported Ru Fe alloy was found to be better than that of supported single Ru or single Fe.Ru/Fe molar ratio in Ru Fe alloy was optimized in this research work.The optimized catalyst Ru₂Fe₁/N-C catalyzed and the apparent activation energy Ea value was calculated to be 33.7 k J·mol^-1.Based on density functional theory?DFT?,the reaction energy barriers of H₂O molecules and NH₃BH₃ molecules on the plane of Ru₂Fe₁?001?,Ru?001?and Fe?110?were calculated,and the lowest reaction energy barriers were found on the Ru₂Fe₁?001?plane.The synergistic effect between Ru and Fe effectively lowered the reaction energy barrier.The combination of non-noble metal Fe and noble metal Ru effectively reduced the cost of the catalyst while maintaining the high catalytic activity of the noble metal.A series of novel supported RuNi alloy catalysts?RuNi/TiO₂@N-C?with heterojunction structure were prepared by using TiO₂@N-C as a support,in which the mixed phase anatase/rutile TiO₂was introduced.Titanium dioxide coated with nitrogen-doped carbon was prepared through the hydrolysis reaction of tetrabutyl titanate,and the reaction between resorcinol and formaldehyde.RuNi/TiO₂@N-C catalysts were used to catalyze the hydrolysis of NH₃BH₃ and Na BH₄ to generate hydrogen.Adding non-noble metal Ni in Ru to form RuNi alloy,decreased the amount of noble metal Ru and increased the utilization rate of Ru.The catalytic performance of supported RuNi alloy was found to be better than that of supported single Ru or single Ni.In the research work,Ru/Ni molar ratio in RuNi alloy was optimized.For comparison,the catalytic activity of RuNi alloy nanoparticles supported on three types of supports?i.e.RuNi/N-C,RuNi/TiO₂and RuNi/TiO₂@N-C?was tested.It was found that TiO₂@N-C showed the best catalytic performance when it was loaded with the nano particles of RuNi alloy.The metal-support interaction between the RuNi alloy and the mixed phase TiO₂effectively enhanced the activity of RuNi nanoparticles in the hydrolysis of borohydrides.The specific rate r _B value of the optimized Ru₁Ni₁/TiO₂@N-C catalyst activation energy Ea value was calculated to be 24.3 k J·mol^-1.The r _B value of the Ea value was 53.7 k J·mol^-1.Compared with similar Ru-based catalysts reported in the literature,the catalyst prepared in this work exhibited an excellent catalytic performance.No significant decrease in activity was observed after 10 cycles in the stability test.It should be of great significance to implement alloying of noble metal and non-noble metal,and to control the composition of noble metal-based alloy nanoparticles and supports simultaneously for development of borohydride-hydrolysis catalyst and particularly for design of new nano-alloy catalyst with excellent catalytic performance.