Catalytic Performances Of Mo-ZSM-5/11 Intergrown Zeolites In Methane And Methanol Co-aromatization Reaction

Methane dehydro-aromatization（MDA）is a potential process that converts natural gas and shale gas into high value-added aromatic products.It is of great significance for the efficient utilization of C1 resources and the activation of C-H bond.Currently,Mo-ZSM-5 is the most widely studied catalyst for MDA reaction.However,the Mo-ZSM-5 catalysts suffer from the low methane conversion and rapid catalyst deactivation due to carbon deposit,which hinders the industrial application of Mo-ZSM-5 catalysts.In this thesis,methane and methanol co-aromatization was investigated using different supports such as ZSM-5,ZSM-11and ZSM-5/11 in the presence of small amout of methanol.The effects of regeneration atmosphere and temperature on the reaction performances were explored.Meanwhile the influence of the alkalimodification was also studied.The main findings are as follows:（1）The catalytic performances of Mo loaded on different supports in the methane and methanol co-aromatization were compared.It is found that methane conversion is related to the pore structure of the support and the state of Mo species.ZSM-5/11 intergrown zeolite was selected as the optimal support.Mo-ZSM-5/11 intergrown zeolite has more isolated Mo species,which is the precursor to the active center and beneficial to the activation of methane.（2）In the methane and methanol co-aromatization reaction the Mo loadings,methane to methanol molar ratios,reaction temperatures,methane GHSVs and regeneration conditions were optimized.It is found that 4Mo-ZSM-5/11 exhibits the best reaction performances when the molar ratio of methane to methanol is 30,the reaction temperature is 750℃ and the GHSV of methane is 1500 h^-1.Under the optimal conditions,methane conversion is up to 14.4%,aromatics selectivity remains above 57.0%,while the selectivity of coke is only 14.5%.The reactivity of the catalyst can’t recover after regeneration in H₂ at 750℃ or 850℃.However,after oxidative regeneration at 470℃,the coke blocking the zeolite channels can be removed.The first and second regeneration could restore the methane conversion and aromatics yield.The activity decreased when increasing the regeneration cycles due to the dealumination of the zeolitic framework.（3）ZSM-5/11 intergrown zeolite was treated with Na OH or n-butylamine,and the reaction performances of 4Mo-ZSM-5/11 catalysts were investigated.The results show that Na OH treatment reduces the crystallinity of ZSM-5/11 intergrown zeolite.Increasing Na OH concentration leads to the serious damage of zeolite structure,which decreases the aromatics selectivity and increases coke selectivity.The ZSM-5/11 relative crystallinity increases slightly upon treatment using n-butylamine,and more isolated Mo species appear.Methane conversion increases 1.2%,aromatics yield increases 0.5%and coke selectivity decreases1.3%for organic alkaline treated catalyst in the methane and methanol co-aromatization reaction.