Preparation Of Transition Metal-Based Composite Catalysts And Catalytic Hydrolysis Of Sodium Borohydride

Sodium borohydride（Na BH₄）can release hydrogen by hydrolysis using suitable catalysts.However,unsupported transition metal catalysts have some disadvantages,such as small surface area,uneven distribution of components,thermal instability and agglomeration of active sites during exothermic process.In order to achieve efficient and stable hydrogen production,three transition metal-based composite catalysts are successfully prepared using hollow carbon material（HNC）supported Co Cu B nanoparticles,graphene coated Co-MOF-74 and TPC supported Ru Co B nanoparticles using hollow carbon material,graphene oxide and three-dimensional porous carbon material（TPC）as the carriers.The main research contents are as follows:（1）First,the pyrrole is polymerized in situ to obtain the polypyrrole support,and then cetyltrimethylammonium bromide is added for modification,and after carbonization,the Co Cu B particles are loaded onto the hollow carbon material by chemical reduction method to obtain Co Cu B/HNC.It is found that Co Cu B/HNC show good catalytic activity for the hydrolysis of Na BH₄,and its hydrogen release rate is 2760.0 m L·min^-1·g^-1 and the activation energy is 26.1 k J·mol^-1 at 303 K.After 5 cycles,the hydrolysis activity of Na BH₄ is 85.7%of the first hydrogen release rate.The advantage of the catalyst is that the hollow carbon material has a porous structure and contains amino groups on the surface.It is conducive to its combination with metal atoms,which increases reaction active sites and electronic conductivity,and the synergistic effect of Co,Cu and B can improve the catalytic activity and stability.（2）Graphene coated Co-MOF-74 is prepared by one step hydrothermal method,and then the graphene-coated Co-MOF-74 composite is obtained by activation（Co-MOF-74@GO）.It is used to catalyze the water-liberated hydrogen of Na BH₄.The Co-MOF-74@GO has a high catalytic activity,and the graphene-coated Co-MOF-74 can maintain the stability of Co-MOF-74 to a large extent.At 303 K,the maximum desorption rate of Co-MOF-74@GO reaches 4566.4 m L·min^-1·g^-1,and the activation energy is 18.1 k J·mol^-1.After5 cycles,the hydrolytic activity of Co-MOF-74@Go to sodium borohydride is 83.5%of the first desorption rate.Since Co-MOF-74 provides hexagonal honeycomb pore structure and unsaturated metal center,and graphene is coated,the catalytic efficiency and stability of the composite are improved.The three-dimensional structure of the composite achieves large specific surface area and rapid electron transport,which significantly improves its catalytic performance.（3）Using Si O₂ as the template and chitosan as the carbon source,a three-dimensional porous carbon material（TPC）is prepared by hydrothermal method,and Ru Co B/TPC is obtained by chemical reduction loading Ru Co B particles.It is found that it significantly improves the dehydrogenation performance of Na BH₄ in alkaline solution,the hydrogen generation rate is 6050.5 m L·min^-1·g^-1,the activation energy is only 23.0 k J·mol^-1,the retention rate of catalyze Na BH₄ hydrogen release after 8 cycles is 85.6%.The results show that the three-dimensional porous structure of TPC can uniformly disperse Ru Co B particles,and the porous structure can provide a large number of reaction channels.The synergistic effect of Ru,Co and B particles increases the catalytic activity of the catalyst.