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

Abstract

The anchoring nature and spatial distribution of rhenium oxide (ReOx) supported on zeolites (ReOx/zeolite) were determined as a function of the support acidity and mesoporosity. The ReOx/zeolite samples were characterized collectively using Argon isotherm, XRD, Raman, XAS, DRIFTS, and organic chemical titrations. The results show that the ReOx species formed the isolated distorted tetrahedral ReO4− structure. On the zeolite support, ReOx species anchored predominantly on Brønsted 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 ReOx species onto both Si-OH+-Al and silanol group (Si-OH). The increase in zeolite mesoporosity migrated the ReOx 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 ReOx in zeolite was explored by direct non-oxidative methane conversion reaction.