Evolution of Mo species and ZSM-5 microstructure with temperature and its impact on methane dehydroaromatisation activity

Abstract

Mo-ZSM-5 is a well-studied catalyst for its ability to convert methane to aromatics and hydrogen. Since the process is thermodynamically ‘uphill’, high temperatures are necessary to achieve acceptable product yields. However, these temperatures have been shown to negatively impact the stability of the zeolite, with the formation of aluminum molybdates being proposed as particularly responsible for framework collapse. Here we use X-ray absorption and optical Raman spectroscopy as well as X-ray diffraction to characterize the initial Mo species present after introduction to ZSM-5, thermal activation and after structural collapse. The results demonstrate that the formation of mononuclear Mo⁶⁺ species coordinated to oxygen is retained despite increasingly high temperature treatment and which is able to perform methane dehydromatisation although with decreasing efficiency as zeolite porosity is lost.