How do the products in methane dehydroaromatization impact the distinct stages of the reaction?
Résumé
Among all the proposed catalytic systems (new supports, synthesis post-treatment, new metal transition, multi-metallic catalysts, etc.) for the methane dehydroaromatization, the initial Mo/ZSM-5 has remained one of the best suitable catalysts, despite its lack of deep understanding. The catalyst evolves throughout four successive stages: calcination, activation, induction, and deactivation. By studying the balance influence between the acid and metal functions throughout its lifetime, the molybdenum and carbon species could be localized, quantified, and identified as well as their roles. An optimal compromise was then established where the catalyst is composed of 4 wt.% Mo with the highest possible acidity. Below these targets, the catalysts with minimal Mo content and low Brønsted acidity display no significant performances. Once this Mo loading is exceeded, zeolite amorphization occurs independently of the zeolite acidity. Actually, in molybdenum excess, a high amount of water is produced during the activation step. The low space velocity of the water flow, its hightemperature initiate reaction on both metallic and acid catalyst functions leading to molybdenum change of morphology and zeolite dealumination, respectively.
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