The Research On Active Phases And The Reaction Mechanism Of Multi-component Catalysts For OCM

Oxidative coupling of methane (OCM) is an important approach to natural gas utilization. Its commercialization can realize the direct conversion of nature gas to ethylene and have very important significance at present. From current researches, it is found that the activity of the catalysts reported for OCM is still not satisfied. The dispersion of the active component and surface active oxygen on the catalyst and their reaction mechanism need to be promoted and explored further. All these problems limit the commercialization of OCM and require to be solved. Thus, in this thesis, six-component Na-W-Mn-Zr-S-P/SiO2 catalysts for OCM were investigated, the reaction mechanism as well.First, we compared the catalysts prepared by incipient wetness impregnation, sol-gel and mixture slurry methods. The catalyst prepared by mixture slurry method showed the best catalytic performance among all samples. In addition, the effects of different addition sequences of Na, W, Mn, Zr, S and P on the catalytic performance of the catalysts were studied. The absence of Na before the addition of Mn and Zr in the catalysts preparation depressed the formation of the active phases of Mn2O3 and ZrO2 and decreased the activities of the catalysts significantly.Secondly, a series of Na-W-Mn-Zr/SiO2 catalysts promoted by different contents of S or/and P were prepared and investigated in oxidative coupling of methane to clarify the effect of S and P on the Na-W-Mn-Zr/SiO2 catalyst. According to the activity test, impressive methane conversion and C2 hydrocarbons yield were obtained at a low temperature of 750℃over the six-component Na-W-Mn-Zr-S-P/SiO2 catalyst, which contain 2 wt% S and 0.4wt% P.For exploring the mechanism of Na-W-Mn-Zr-S-P/SiO2 catalysts for OCM deeply, we studied the process of oxidative dehydrogenation of ethane to ethylene. The effects of different preparation methods and the addition of S and P components of catalysts on the ethane dehydrogenation are investigated. It was found that the catalyst of pronounced activity for OCM usually had corresponding ability to catalyze the ethane dehydrogenation by O2 or CO2 as well. Moreover, the effects of reaction conditions on oxidative dehydrogenation of ethane with O2 or CO2 were discussed.Finally, the reaction mechanism of OCM and the oxidative dehydrogenation of ethane were proposed by using the technology of in-situ Diffuse Reflectance Infrared Fourier transform Spectroscopy (DRIFTS).