In And Pd Additives On The Mo/hzsm-5 Catalyst Methane Aromatization Of Modified Research

Direct transformation of methane to higher hydrocarbons such as aromatics has been a great challenge in heterogeneous catalysis and a fascinating way for reasonable utilization of natural gas resources. Recently, methane dehydrogenation and aromatization under non-oxidative conditions over Mo/HZSM-5 catalyst have received wide attention. But this catalyst generally shows low conversion of methane and poor stability, owing to irreversible coke formation on the catalyst. Introduction of second metal species into Mo/HZSM-5 has been believed to be a promising route to improve methane non-oxidative transformation and enhance catalyst stability. We tried to modify the catalyst by introducing In and Pd metal.The Mo-In/HZSM-5 catalyst exhibits better catalytic performance compared to unpromoted Mo/HZSM-5 catalyst. It is found that the addition of In to Mo/HZSM-5 markedly improve the conversion of methane and greatly enhances the yield of aromatics along with effective reduction of coke formation. NH3-TPD shows that the addition of In onto Mo/HZSM-5 causes further increase in the amount of weak acid strengths and at the same time, not creates the strong acid sites. TPR study illustrates that the existence of hi promotes the reduction of Mo species. The impregnation sequence of Mo and In transition metal cations during the catalyst preparation is also important for good catalytic performance. The co-impregnated Mo-In/HZSM-5 catalysts exhibit the best catalytic activity for methane non-oxidative conversion, which effectively inhibits the formation of coke.As we know, the palladium metal is more active for dehydrogenation of methane and the CHX coupling reactions than other transition metals. Thereby, we expect that the addition of Pd will be beneficial to both catalytic activity and stability.Indeed, we find that 0.4% Pd loading into Mo/HZSM-5 resulted in increases of methane conversion from 11.54% to 15.23% and aromatics selectivity from 67.83% to 79.52% owing to the suppression of coke from 24.61 to 16.72% as compared with Mo/HZSM-5. The different impregnation sequence and preparation method were investigated. The results show that co-impregnated Mo-Pd/HZSM-5 catalysts exhibit best catalytic performance. The effect of different pretreatment gas has been studied. It is also found that the catalyst pretreated by feed gas show better stability than these by Ar steam. TPR, BET, NH3-TPD and XPS were used for catalyst characterization. Carbon accumulation on the catalyst is studied by means of DTA and TG methods. It is demonstrated that the addition of Pd to Mo/HZSM-5 considerably enhances the catalyst ability and reduces the carbon deposition on the catalyst.