(429d) Catalyst Design Strategies for Multifunctional Metal-Promoted Zeolites in the Conversion of Natural Gas to Aromatics

Valorization of methane to aromatics and hydrogen, by the one-step non-oxidative methane dehydroaromatization reaction (6 CH₄ → C₆H₆+ 9H₂), MDA, is an attractive route for natural gas upgrade since it can be implemented at, or near, the gas source, offering the opportunity for development of modular technology for distributed manufacturing of aromatics while reducing processing and transportation costs. Our group has been carrying out a systematic study of this catalytic process with the aim of answering long-standing fundamental questions related to MDA chemistry which will enable development of strategies to mitigate the technological challenges associated with MDA. Zeolite-supported molybdenum catalysts are the most effective MDA catalysts studied so far, but they do not possess conversion and stability requirements for commercialization. Molybdenum carbide species are thought to constitute the active sites for MDA and are formed when the zeolite-supported Mo oxide species in the as-prepared catalysts are exposed to methane in the first minutes of reaction. In this talk I will describe how our group has discovered that the activation protocol employed to form the active molybdenum carbide sites plays a critical role in catalyst stability. I will also present how our studies on the effect of the zeolite acidity employing in situ/operando X-ray absorption spectroscopy suggest that the structure of local environment of the as-prepared molybdenum oxide sites does not affect the catalyst performance, underpinning the importance of controlling the carbide formation step. I will also discuss our most recent results indicating that the addition of small amounts of a second transition metal promoter, such as cobalt and nickel, while employing our new activation protocol, results in further enhancement of catalyst stability.