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

Wu, Yiqing, Holdren, Scott, Zhang, Yuan, Oh, Su Cheun, Tran, Dat T., Emdadi, Laleh, Lu, Zheng, Wang, Mei, Woehl, Taylor J., Zachariah, Michael, Lei, Yu, Liu, Dongxia
Journal of catalysis 2019 v.372 pp. 128-141
Bronsted acids, Raman spectroscopy, X-ray absorption spectroscopy, X-ray diffraction, acidity, methane, micropores, protons, rhenium, zeolites
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.