Quantification of rhenium oxide dispersion on zeolite: Effect of zeolite acidity and mesoporosity

Abstract The anchoring nature and spatial distribution of rhenium oxide (ReO x ) supported on zeolites (ReO x /zeolite) were determined as a function of the support acidity and mesoporosity. The ReO x /zeolite samples were characterized collectively using Argon isotherm, XRD, Raman, XAS, DRIFTS, and organic chemical titrations. The results show that the ReO x species formed the isolated distorted tetrahedral ReO 4 − structure. On the zeolite support, ReO x species anchored predominantly on Bronsted acid sites (Si-OH + -Al) enclosed in micropores (internal acid sites), by replacing the protons in Si-OH + -Al sites at a H + /Re ratio of ∼1.1 in zeolites with high acidity. The decrease in zeolite acidity led to the anchoring of ReO x species onto both Si-OH + -Al and silanol group (Si-OH). The increase in zeolite mesoporosity migrated the ReO x species onto both internal acid sites and those on the external surface and mesopores (external acid sites), as well as Si-OH groups. The implication of distribution of ReO x in zeolite was explored by direct non-oxidative methane conversion reaction.