Tuning selectivity of acetic acid and alcohols by Brønsted and Lewis acid sites in plasma-catalytic CH4/CO2 conversion over zeolites

Abstract

Plasma catalysis enables CH4/CO2 direct conversion to oxygenates under mild conditions. However, addressing complexity of oxygenate products is the main scientific challenge. Herein, the roles of Brønsted and Lewis acid site (i.e., BAS and LAS) in tuning the selectivity of acetic acid and alcohols have been comparatively investigated for the first time. BAS and LAS are provided by HZSM-5 and 13X zeolites, respectively, and their amounts are adjusted by steam treatment. Results reveal that BAS significantly promotes acetic acid formation, while LAS favors alcohols generation. In addition, Au supported zeolites show that Au3+-BAS synergy exhibits potential for acetic acid. In-situ FTIR spectra identify the bicarbonate (HCO3,ad) and formate (HCOOad) to be the primary surface species on BAS and LAS, respectively. Correspondingly, the pathways for acetic acid and methanol production are proposed based on catalyst characterizations and plasma diagnosis. This work opens up zeolite-based catalysts for selective CH4/CO2 conversion to oxygenates.