Acid Catalysis over Crystalline Zr<sub>3</sub>SO<sub>9</sub>: Role of the Local Structure in Generating Acidity
Meilin Tao, Satoshi Ishikawa, Takuji Ikeda, Shunsaku Yasumura, Kosuke Shimoda, Ryota Osuga, Yuan Jing, Takashi Toyao, Ken‐ichi Shimizu, Hiromi Matsuhashi, Wataru Ueda
Abstract
Sulfated zirconia (ZrS) has been widely used as an acid catalyst in industrial processes for the isomerization of n -alkanes. Despite the excellent catalytic properties of this material, its catalytically active structure has been hardly identified to date. In this study, we investigated the crystal structure and acid properties of crystalline Zr 3 SO 9, which was reported 30 years ago by Kato et al. Zr 3 SO 9 was a hexagonal-shaped plate consisting of a (101) plane of the tetragonal ZrO 2 phase with S species uniformly dispersed in the form of SO 4 2– . Zr 3 SO 9 exhibits an outstanding catalytic activity for acid reactions, which is superior to those of typical acid catalysts. The introduction of H 2 O into Zr 3 SO 9 altered the nature of the acid sites, and almost all Lewis acid sites (LAS) were transformed into Brønsted acid sites (BAS). Spectroscopic analyses and density functional theory calculations revealed that the Zr sites adjacent to SO 4 2– functioned as a LAS, while the H 2 O coordinated to this Zr site acted as a BAS. Moreover, Pt-loaded Zr 3 SO 9 demonstrated a stable catalytic activity in the isomerization of n -butane under continuous gas-flow conditions, which was significantly higher than that of Pt-loaded ZrS that is employed as an industrial catalyst for this reaction.