Abstract
The Zn-loaded zeolite ZSM-5 is an active and promising catalyst for the conversion of methanol to aromatics with high yield. In this work, we have investigated the catalytic performance of shaped Zn-ZSM-5/alumina catalysts in this reaction at industrially relevant pressures. This has been combined with extensive characterization to identify the active Zn species. It is clear that the introduction of Zn leads to an improved catalyst lifetime when the reaction is carried out at elevated pressure. A clear shift from reaction pathways leading to alkane formation to pathways leading to molecular hydrogen formation during the production of aromatics is observed. For industrial catalysts, Zn incorporation is conveniently carried out by impregnation after shaping. A significant migration of Zn into the zeolite ion exchange positions is observed upon calcination of impregnated catalysts, and it is these species that are active for the reaction. At high Zn loadings, ZnAl2O4 species observable by X-ray absorption spectroscopy, but not detectable by diffraction, are formed in the alumina binder.
Highlights
Zeolites and zeotypes are extensively studied inorganic materials due to their practical application as heterogeneous catalysts for several industrial processes [1,2,3,4,5,6]
The zeolite framework provides the system with shape selectivity properties, and the extra Lewis acid sites from the transition metal add an additional dehydrogenation activity
We have investigated the catalytic performance of these materials for the conversion of methanol to aromatics
Summary
Zeolites and zeotypes are extensively studied inorganic materials due to their practical application as heterogeneous catalysts for several industrial processes [1,2,3,4,5,6] Among these applications, the methanol-to-hydrocarbons conversion processes (MTH) have acquired remarkable importance in the last decades, as these are a promising nonpetroleum alternative for the production of highoctane gasoline or base chemicals such as short-chain olefins or light aromatics [7,8,9]. We aim to study the effect that Zn has on MTA performance for real catalysts and how the dehydrogenation activity varies depending on the location of Zn, type of sites, and Zn content With this purpose, we have produced a spherelike catalyst by spray-drying a slurry containing ZSM-5 and alumina. Our main objective is to understand which kinds of metal sites are formed and how they are distributed between the zeolite component and the binder phase within the shaped catalysts and how this affects the catalytic performance
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