Synthesis And Extruded Molding Of Mo/HMCM-22Catalyst In Methane Dehydroaromatization

Methane dehydroaromatization reaction (MDA), as a promising route to product chemical raw materials, has made it possible to converse the methane into high value-added chemicals directly, such as benzene and naphthalene. The reaction possesses the comprehensive utilization of natural gas and the value of industrial applications. Up to date, many important features on the development of catalysts and reaction mechanism have been achieved; moreover, the deactivation of the catalyst with time on stream is very intractable, which restricted the industrial application of MDA reaction.Mo/HMCM-22is one of catalysts which possess the competitive catalytic activity in MDA reaction. In this dissertation, a feasible way was explored to combine the hierarchical structure and acidic modification with the assistance of carbon particles and fluoride ions for Mo/HMCM-22catalyst to improve catalytic performance and inhibit the formation of coke in MDA reaction. Subsequently, an industrial application of extruded molding technology was explored to research the influence of the molded catalysts in MDA reaction. The main discussions and conclusions were as follows:(1) Hierarchical MCM-22zeolite blocks were hydrothermally synthesized without any second template. It is favorable for the blocks to form the high-degree crystallinity under high-temperature crystallization process. The size of the blocks was about10-20μm, which possessed hierarchical pore structure. The initial CH4conversion and benzene yield were15.9%and5.9%, respectively, and the benzene yield was4.5%after32h.(2) Hierarchical pore structure MCM-22zeolite aggregates (MCM-22-FC) were prepared by one-pot hydrothermal synthesis with the assistance of carbon particles as a template and fluoride ions as an acidic property modifier. The MCM-22-FC aggregates were constructed by many thin lamellas with high crystallinity and possessed the hierarchical pore structure, which improved the mass transport of large molecule products. Mo/HMCM-22-FC catalyst exhibited an improved catalytic performance in MDA reaction. The benzene yield reached the highest value of7.8%and kept above6%even after52h.(3) With the assistance of the fluoride ions in the synthetic gel, the acidic strength and acidic amount of hierarchical MCM-22-FC aggregates were reinforced evidently. KF as the fluoride source was favorable to form the units which acted as the electron inductive effect to increase the Br(?)nsted acidic amount. Thus, MCM-22-FC aggregates involved more Mo species to migrate into channels and formed more active MoCx and MoOxCy species. The less Br(?)nsted acid sites remained in Mo/HMCM-22-FC catalyst after forming plentiful active species, inhibiting the formation of coke and improving the aromatic selectivity and catalyst life.(4) The extruded Mo/HMCM-22-FC catalysts were prepared though mechanical mixing method with different binders. HFC-Mo(SiO2) catalyst, with SiO2as the binder, voluminously kept the morphological structure of hierarchical parent aggregates and catalytic performance of the parent catalyst. The initial CH4conversion and benzene yield were16.6%and6.5%, which were2%and15%lower than the parent catalyst, respectively, and the benzene yield was3.0%after47h.