Study On The Mechanism Of Carbon Black Inducing Activated Carbon To Enhance Hydrogen Production By Chemical Looping Methane Decomposition

The proposal of the carbon peaking and carbon neutrality goals puts forward higher requirements for building a green and efficient energy system in China.As a clean and efficient secondary energy source,hydrogen energy is considered to be one of the most promising alternative energy and clean fuels.Methane Catalytic Decomposition（MCD）is known as a potential and environmentally friendly hydrogen production technology because its products are only solid carbon and hydrogen.Usually,catalysts are needed to reduce the reaction temperature.Carbon-based catalysts are widely studied because of their excellent catalytic performance,low cost and wide sources.Among them,activated carbon（AC）has high initial activity,but its deactivation rate is very fast due to carbon deposition.In contrast,carbon black（CB）can maintain catalytic activity well in the later stage of the reaction,but its density and particles size are small,and flowability is poor,which is not conducive to the transfer of carbon deposits during the reaction process.Therefore,in this thesis,AC is used as the carrier surface to load defective CB to prepare CB/AC composite catalyst,so that the carbon deposit generated by methane cracking can partially copy the defective structure of carbon black,and constantly generate new catalytic active sites to effectively reduce the deactivation rate.Through characterization technology,molecular simulation and other means,the stacking mode of carbon deposit defect structure growth and replication is clarified.The mechanism of methane adsorption reaction on AC under different influencing factors has been revealed,and a highly efficient mechanism for inducing defect structure self-replication and deactivation through coupling with heterogeneous carriers has been established.The specific contents are as follows:First of all,carbon black BP2000 and AC from coconut shell were used to prepare AC_N+BP2000-20:1/20:3/20:5 composite catalysts by impregnation method.The experiments of methane decomposition were carried out at 850℃,900℃and950℃to evaluate catalytic performance and explore the optimal load ratio.The results showed that when HNO₃modification and CB loading were combined,the conversion of methane and hydrogen yield were significantly promoted.The initial activity is significantly enhanced and the stability is slightly improved in the later stage,and the effect of delayed deactivation is more obvious with the increase of temperature,among which the AC_N+BP2000-20:3 catalytic activity is the most.Secondly,SEM,TEM,TGA,O₂-TPO,BET,XPS,XRD and other characterization methods were used to explore the relationship between the microstructure,lattice defects and active site of the catalyst and its reaction rate.The results indicated that carbon black loading and nitric acid modification significantly increased the micropore volume of activated carbon,changed the types and quantities of surface functional groups,and significantly increased defect concentration.And micropores played a key role in the initial stage of methane decomposition,where methane filled rapidly and interacted with activated carbon.The edge,vacancy and topological defects of graphene layer of the protruding deposited carbon induced by CB loading provide active sites for the reaction to promote methane conversion,delay the deactivation of catalyst and improve activity stability in the later stage.Finally,the mechanism of different factors on the adsorption of methane on activated carbon was explored by Sorption and Castep modules of Material Studio,including pore structure,surface functional groups and defect structure.It is found that the smaller the micropores,the stronger the adsorption performance.And there is a positive correlation between methane adsorption capacity and pore volume.The functional groups can promote the adsorption,but the decrease in effective volume fraction limits the amount of methane adsorbed.In addition,carboxyl and pyrrole groups preferentially cleave hydrogen bonds to expose active sites,which then undergo cleavage by interacting with CH₄.The topological defect enhances the non localization properties of the density of states s and p orbitals,promoting the interaction between AC and CH₄.