The Study On Preparation Of Non-noble Metal Cobalt-based Catalysts And Their Catalytic Performance For Dehydrogenation Of Formic Acid

Hydrogen energy is considered as the most promising new energy in the future due to its clean,pollution-free and high energy density,which is a significant method to solve the problems of resource exhaustion and environmental pollution.However,the storage and transportation of hydrogen has be en the bottleneck restricting the large-scale application of hydrogen energy,which is the key development field in the future of hydrogen era.As a safe,non-toxic and renewable liquid with convenient transportation and low cost,formic acid（HCOOH）can be decomposed into hydrogen under catalyst and be used as a hydrogen carrier to realize the safe storage and transportation of hydrogen.But the difficulties in separation and recovery of homogeneous catalysts and the high cost and scarcity of precious metals are the most prominent weakness of formic acid hydrogen storage system.Therefore,it is vital to develop non-noble metal heterogeneous catalyst with low cost and high activity for hydrogen production from formic acid decomposition.In this paper,the non-noble metal heterogeneous cobalt-based catalysts are prepared by using graphite carbon nitride（g-C₃N₄）as a sacrificial template through the pyrolysis and used for the dehydrogenation of liquid formic acid,whose microstructure characterization and catalytic performance are investigated.This thesis mainly included the following contents:Firstly,the metal-nitrogen-carbon（M-N-C）catalysts have been widely studied due to their unique electronic structure,controlled coordination environment and high atomic utilization.Herein,M-N-C（M=Fe,Co,Ni,Cu,Zn,Mn）catalysts are firstly synthesized via using g-C₃N₄ as a sacrificial template.Experimental analysis shows that compared to other M-N-C catalysts,the Co-N-C catalyst has better catalytic performance for the dehydrogenation of formic acid.The selectivity of H₂ is nearly100%and the gas production rate(GPR_（Co）)is as high as 14483 m L g _Co^-1 h^-1.Various characterization results indicate that the transformation of the sacrificial template into an N-doped carbon matrix during the pyrolysis process facilitate s the formation of atomic Co-N-C sites to enhance catalytic activity,and then the maximum loading amount of Co is up to 6.91%.Moreover,it is found that the N content inside catalysts is critical to catalytic activity,whose amount can be successfully tuned by the choosing of different types of sacrifice template s and the pyrolysis temperature.The optimal catalytic performance appears and the optimal N content is 7.66%,when g-C₃N₄ is prepared via urea and the pyrolysis temperature is 800℃.Secondly,the g-C₃N₄ continues to be used as a sacrifice template,and the Co and N ligand are replaced by MOFs as precursors with regular structure and easy to regulate.In other words,the Co＆Co N-C catalysts are synthesized by the sacrificial template g-C₃N₄ nanosheets（CN）and bimetallic zeolite imidazol ate framework materials（ZIFs）through pyrolysis.Their microstructures are optimized and the corresponding effects on the catalytic performance are studied.Preliminary analysis shows that the addition of CN can cover the crystal structure of ZIF s,thereby reducing the loss of Co during pyrolysis and affect the dehydrogenation activity of Co＆Co N-C catalysts with the Zn/Co metals ratio.The optimal catalytic performance appears and the gas production rate(GPR_（cat）)is 528 m L g^-1_cat h^-1 when the addition amount of CN is 0.3 g and the Zn/Co metals ratio is 0.5.In this paper,the non-noble metal heterogeneous Co-based catalyst with low cost is developed,which is expected to be a new type of hydrogen energy storage and conversion catalyst and lead a new avenue for developing highly efficient heterogeneous catalysts for dehydrogenation of formic acid.