ゼオライト触媒の固体酸性度ならびにその触媒反応への酸度関数H₀の適用性

抄録

The dehydration of isopropanol has been studied at 180-220°C with zeolite Y catalysts which were ion-exchanged (CaKY, LaKY), decationized (HKY, HNaY) or de-aluminated (d-HNaY) up to various levels. The solid acidity of each catalyst was determined as the acidity function H₀ from absorption spectra of an acid-base indicator absorbed on the catalyst in decaline. The acidity of catalysts and their catalytic activity were generally enhanced with increasing exchange or pretreatment. But excessive decationation or de-alumination caused deactivation due to partial destruction of the crystalline lattice. As seen in Figs. 10 and 11, experimental data shows good linear relations between log k₀, the zero order rate constant, and H₀. This linearity is theoretically supported by assuming a surface reaction mechanisms analogus to homogenous acid catalysis. The line slopes were less than unity in absolute value and varied somewhat with the respective catalyst as seen in Table 1, suggesting a proton mobility characteristic for zeolite. The application of H₀ to solid acid catalysis was considered to be available by supposing a correction of pKa of indicators suitable to the surface or intracrystalline state.