Title : Effect of temperature on Cr promotion of Mo2C supported on sulfated Zirconia for methane dehydroaromatization
The shale gas revolution has made immense and previously unattainable resources of natural gas accessible and economically competitive. A major component of natural gas is methane, which is typically used for power generation or is flared. Methane dehydroaromatization (MDHA) is a process in which methane can be converted into valuable hydrocarbons, including ethylene and benzene. Mo oxide supported on ZSM-5/MCM-22 has been well-studied in recent years for MDHA. It is generally thought that Mo carbides are responsible for activating methane by forming CHx species. These are dimerized into C2Hy species, which are then oligomerized on the acidic zeolite sites available on ZSM-5/MCM-22 support, leading to aromatics. In these catalysts, sulfated zirconia (SZ) can provide the acid sites. In present work, Cr is introduced as promoter for Mo2C/SZ. Cr has been previously added along with other metals in ZSM-5 in the form of extra-framework species to facilitate the catalyst dehydrogenation function for MDHA. 0.5 wt. % of Cr was added to a 5 wt.% Mo/SZ by incipient wetness impregnation. DRIFTS was use to characterize the surface acidity of chemisorbed pyridine.
The reactions were run at 600?C, 650ºC and 700ºC for 15 hours to study the promotional effect of Cr for MDHA. The catalyst was first reduced under H2 till it reached the desired reaction temperature. It was carburized subsequently under 1:4 CH4:H2 ratio for 4 hours before starting the reaction. Products observed were ethylene, ethane, propylene, with aromatics including benzene, toluene and ethylbenzene. The promotion of Cr increased with temperature, as observed by higher methane conversion as well as high ethylene and benzene yield. However, at higher temperatures, deactivation occurred rapidly. This was likely due to coking on catalytic surface, later confirmed by TPO.