Synthesis And Properties Studies Of Catalyst With Metal Nanoparticles Supported On MXene

Recently,the worldwide concerns on energy crisis and environmental pollution have stimulated intensive attention,which is essential to pursue sustainable and renewable energy.Hydrogen energy is regarded as one of the ideal clean energy in the future due to its advantages of environmental friendly,high abundance and high energy density.Among numerous hydrogen storage materials,chemical hydrogen storage materials such as hydrazine hydrate and ammonia borane with high hydrogen storage density and good chemical stability under ambient conditions,have been considered as the leading contenders in promising chemical hydrogen storage materials for various applications.The key point of large-scale application of hydrogen energy is the rapid and complete decomposition of hydrogen storage materials such as hydrazine hydrate and ammonia borane by low-cost catalysts at a low temperature range?273-353 K?.In this paper,a series of metal nanoparticles?NPs?supported on two-dimensional nano-material MXene to release hydrogen from hydrazine hydrate or ammonia borane were designed and synthesized.The main contents includes the following points:?1?The preparation methods of RhNi NPs anchored on MXene surfaces and the effect mechanism of strong metal-support interaction on the decomposition performance of hydrazine hydrate were investigated.RhNi/MXene with different molar ratios were prepared by supporting RhNi NPs onto MXene surface with sodium borohydride as reductant.The as-prepared RhNi/MXene catalysts were applied for hydrogen generation from hydrous hydrazine.TEM images showed that Rh_0.8Ni_0.2 NPs were uniformly dispersed on the surface of MXene,with an average particle size of 2.8 nm.Rh_0.8Ni_0.2/MXene catalysts had the best catalytic activity among all catalysts under 50^°C,alkaline condition.Rh_0.8Ni_0.2/MXene catalysts demonstrate 100%H₂ selectivity,excellent durability,and high reaction kinetics with turnover frequency value of 857 h^-1toward hydrazine hydrate decomposition in alkaline solution,the activation energy was calcultated as 38.2 kJ·mol^-1.The excellent catalytic performance is attributed to the synergistic effect between Rh-Ni and the strong metal-support interaction between MXene and RhNi NPs.?2?In order to further investigate the effect mechanism of the strong metal-support interaction between the MXene and metal NPs on the catalytic performance,the MnO_x-MXene bi-support system was synthesized by co-reduction of Mn.The as-prepared RhNi/MnO_x-MXene catalysts were applied for hydrogen generation from hydrous hydrazine.The ultrafine RhNi nanoparticles were well dispersed on the bi-support?MnO_x-MXene?surface.The optimized Rh_0.7Ni_0.3/MnO_x-MXene NPs exhibit excellent catalytic properties,and the corresponding TOF value can reach 1101.9 h^-1 with 100%H₂ selectivity under 50^°C and the activation energy toward hydrazine hydrate decomposition was calcultated as 36.8 kJ·mol^-1.Rh_0.7Ni_0.3/MnO_x-MXene catalyst also had high durability toward hydrous hydrazine decomposition,even after 6 cycles of the catalytic reaction,no apparent decrease was seen and high H₂ selectivity was still maintained well.The XPS results show that the remarkable catalytic performance is attributed to the strong metal-support interaction of MnO_x-MXene bi-support to RhNi NPs,which enhanced the electron density of RhNi NPs.?3?The preparation methods of non-noble metal NPs anchored on MXene surfaces and the effect mechanism of strong metal-support interaction on the decomposition of ammonia borane were investigated.Co NPs were supported on the surface of MXene by one-step wet-chemical method and the as-prepared Co/MXene catalyst was applied for hydrogen generation from ammonia borane.The synthesized Co nanoparticles were monodispersed on MXene surface with the size of 3.2 nm.The TOF value was 2394 h^-1for the hydrolysis of ammonia borane under 50^°C with 100%H₂ selectivity and the activation energy for the decomposition of ammonia borane was calcultated as 33.05kJ·mol^-1.MXene played an important role in promoting the uniform dispersion and inhibiting the agglomeration of Co NPs.?4?In order to further investigate the effect of the synergistic effect between alloy NPs and the strong metal-support interaction between MXene and non-noble metals on the catalytic performance of ammonia borane hydrolysis,CoNi NPs were supported on the surface of MXene by co-reduction method to prepare CoNi/MXene catalysts for promoting hydrolysis of ammonia borane.It was found that among the CoNi/MXene,Co_0.7Ni_0.3/MXene catalyst showed the best performance toward catalyzing ammonia borane decomposition with a TOF of value of 5256 h^-1.The activation energy for hydrolysis of ammonia borane was calcultated as 30.39 kJ·mol^-1.The remarkable catalytic performance is attributed to the strong metal-support interaction between MXene and CoNi NPs and the synergistic effect between Co-Ni.