Design And Synthesis Of Supported Metal Photocatalysts For High-efficiency Hydrogen Generation From Ammonia Borane And Their Performance

As a new kind of clean energy,hydrogen can not only reduce the consumption of non-renewable energy,but also mitigate environmental problems,and then has gradually become the focus.The room-temperature stable and non-toxic ammonia borane（NH₃BH₃）has high hydrogen content of 19.6 wt%,which is considered as the ideal and promising hydrogen energy carrier.However,at present,the system of the hydrogen production from NH₃BH₃（NH₃BH₃+2H₂O?NH₄BO₂+3H₂）has many problems,such as the low catalytic activity and high cost of catalysts.Therefore,the key is to rationally design catalysts with high activity.On the basis of above considerations and from the perspective of high-efficiency hydrogen generation from NH₃BH₃,we have prepared a series of supported metal nanocatalysts and studied their catalytic performance under the visible light irradiation.The main results are listed as following:（1）A series of highly dispersed and visible-light-responsive Ru nanocatalysts supported by oxides TiO₂,ZrO₂,Al₂O₃ and SiO₂ have been prepared using high-temperature H₂ reduction method.The influences of metal loadings,reduction temperature,reduction method and supports on the performance of hydrogen generation from NH₃BH₃ have been systematically investigated.The results show that the size and dispersion of Ru nanoparticles on support and the interaction between metal and support are the main factors influencing the photocatalytic hydrogen generation.Among all the catalysts,TiO₂-supported Ru catalyst,which has a metal content of 1.0 wt%and is parpared in H₂ atmosphere and at 400 ^oC,has the high photocatalytic activity,featuring the turnover frequency（TOF）value of 1034.5min^-1.This value is much higher than the values of reported Ru based catalysts.（2）A series of graphitic carbon nitrides（C₃N₄）have been synthesized by differentprecursors,which have been used as supports to prepare non-noble metal nanocatalysts using in-situ reduction method.Also,the catalytic performance of catalysts containing different C₃N₄ has been investigated under visible light irradiation.The results show that different C₃N₄ prepared by different precursors have different morphologies,band structures and separation efficiency of the photoexcited carriers,which are the main factors influencing the catalytic performance of catalysts.Among all the catalysts,the Co catalyst based on C₃N₄ parpared using urea exhibits the highest hydrogen-generation activity under visible light irradiation.（3）A series of visible-light-responsive non-noble metal nanocatalysts supported by oxides SiO₂ and ZrO₂ with different crystallinity have been prepared using in-situ reduction method.The influence of different crystallinity of support on the performance of hydrogen generation from NH₃BH₃ has been systematically investigated.The results show that the crystallinity of metal and supports strongly affect the activity of catalysts and the catalysts with low crystallinity have more defects,which is beneficial for the improvement of catalytic activity.Among all the catalysts,the catalysts with amorphous state of metal nanoparticles and support exhibit the high activity.Especially,amorphous SiO₂-supported amorphous Co nanoparticles exhibit the highest photocatalytic activity,featuring the TOF value of203.6 min^-1.