Catalytic Performances Of Modified Mo/HZSM-5 In Non-oxidative Methane And Methanol Co-aromatization

Methane is the most stable organic molecule,and its selective activation and targeted conversion are the main challenges in the field of catalysis.Methane is abundant,and can be directly converted into high value-added aromatics through the methane non-oxidative aromatization?MDA?reaction.This is very important for the utilization of methane.Mo/HZSM-5 is one of the most promising catalysts in MDA reaction.However,the catalyst has poor stability and is very easy to deactivation by coking.In this thesis,the methane non-oxidative aromatization in the presence of a small amount of methanol was studied.The variations of the structure and acidity of Mo/HZSM-5 catalyst before and after alkali modification were investigated.Its correlation to the activity of MDA reaction and the capability of coke resistance were also investigated.The main findings are as follows:?1?The catalytic performance of Mo/HZSM-5 for MDA reactions in the presence or absence of methanol was compared.The results show that the conversion of methane increases from 4%to 10%,the selectivity of benzene remains stable at 70-80%,and the coke content decreases from 15 wt%to 5 wt%when the optimum molar ratio of methane to methanol is 20.The effects of HZSM-5 with different Si/Al ratios,different Mo contents,reaction temperatures and methane GHSVs on the reaction performances were thoroughly optimized.The results show that when Si/Al ratio is 35,Mo loading is 6 wt%,the reaction temperature is 700?and GHSV of methane is 2000h^-1,methane has the best conversion up to 10%,and the selectivity of benzene increases to about 70%.?2?HZSM-5 zeolite was treated with different concentrations of TPAOH,NaOH and TPAOH/NaOH combination,then loaded with Mo.Their structures,acidity and the reaction performances before and after alkali treatment were compared.The results show that after optimized 0.1 M TPAOH modification,the conversion of methane maintains to about 5-8%,the selectivity of benzene remains above 60%and the selectivity of C₇-C₉ aromatics increases.After NaOH modification,HZSM-5 shows serious desilication and dealumination,which results in the decrease of methane conversion and aromatics selectivity.When the concentration of TPAOH increases in alkali combination,the zeolite structure could be protected and the reaction performance decreases less.TG and TPO results shows that the coke content decreases to about 1.4 wt%after alkali treatment and the amount of polycyclic aromatics decreases,which improves the stability of the catalyst.