Preparation Of Cu-based Nanoparticles Supported On Porous Boron Nitride And Their Catalytic Performance For Hydrolytic Dehydrogenation Of Ammonia Borane

Among the various kinds of hydrogen storage materials,ammonia borane is widely recognized because of its high hydrogen storage content(19.6 wt%).Hydrogen can be released from ammonia borane gently and effectively by hydrolysis.The selection of catalysts is very important for the occurrence of hydrolysis reaction and the rate of hydrogen release.Non-noble metal catalysts have many advantages such as rich resources and low cost.However,the transition metals with small particle sizes are easy to agglomerate,which would mask the active sites and reduce catalytic activity.It is of great significance to find a suitable matrix to support the transition metal nanoparticles,so that more active sites can be exposed in the catalysts,thereby the catalytic effect can be improved.Porous boron nitride(BN)materials not only have excellent high thermal and chemical stability,but also have rich pore structure and high specific surface area.So they have great potential for development in the fields of hydrogen storage,water pollution treatment and so on.In this thesis,porous BN material is used as the effective catalyst carrier.The BN-supported Cu-based catalysts are synthesized by an impregnation reduction method.Then,the performance of the composite catalysts for hydrogen production by hydrolysis of ammonia borane are studied,and the effect of porous BN support on the activity of the catalyst is analyzed.The main contents are as follows:1.By using impregnation reduction method,CuCo nanoparticles were supported on porous BN nanofibers(BNNFs)to obtain Cu_xCo_1-x/BNNFs(x is the metal molar ratio)catalysts.The CuCo metal particles are uniformly dispersed on the surface of BNNFs.The synthesized Cu_0.4Co_0.6/BNNFs catalyst with a loading weight of 15.6 wt%exhibits excellent catalytic activity in the hydrolysis of ammonia borane to produce hydrogen,with the hydrogen generation rate of 3387.1 m L·min^-1·g^-1 and activation energy of 21.8 k J·mol^-1.After 5 cycles,the catalytic activity remains 55%of the original.Theoretical calculations indicate that the synergistic effect of CuCo binary metal and the strong interaction between BN support and CuCo metal lead to the enhancement of catalytic activity of the catalyst.2.The Cu_xNi_1-x/BNNFs(x is the metal molar ratio)catalysts were prepared by impregnation reduction method,and their catalytic performance for hydrogen production by hydrolysis of ammonia borane was studied.The Cu_0.67Ni_0.33/BNNFs catalyst with metal loading of 14.3 wt%exhibits the highest catalytic activity.Its activation energy is 26.7k J·mol^-1,which is much lower than that of unsupported Cu_0.67Ni_0.33 particles(41.3 k J·mol^-1),indicating that the addition of BNNFs can reduce the activation energy of the reaction and promote the release of hydrogen.The superiority of BNNFs carrier is also applicable to Cu Ni catalytic system,which can be used as a reference for the application of BN carrier in other system catalysts.3.The CuCo nanoparticles were supported on BNNFs,porous BN microfibers and commercial BN nanosheets,respectively.The morphology,catalytic activity and cycle stability of the composite catalysts were characterized and compared,and the effect of BN supports on the activity of the catalysts was investigated.Compared with commercial BN nanosheets which have low specific surface area and almost no pores,the porous BN with high surface area and rich pore structure can contribute to the dispersion of metal particles,the exposure of more metal active sites and the decrease of reaction activation energy,which are very beneficial to improve the activity of metal catalysts.4.In order to further study the interaction mechanism between BN support and metal particles,Co/BNNFs catalyst was synthesized.The morphology and catalytic activity of Co/BNNFs catalyst have been compared with that of CuCo/BNNFs binary catalyst.The introduction of Cu element is helpful to reduce the metal particle size and improve the catalytic activity.Through the study of the electron transfer of various elements in Co/BNNFs and Co catalysts and their catalytic activity for the hydrolysis of ammonia borane,it is proved that there is a good interaction between metal Co and BNNFs support,and this interaction will lead to the improvement of catalyst activity.