Relation between the Hydroxylation State of Zirconia, the Sulfate Promotion Method, and the Catalytic Activity of SO42−–ZrO2Catalysts

Abstract

Zr(OH)4samples were prepared from ZrOCl2and ZrCl4; they were calcined at temperatures between 100 and 620°C and were sulfated with H2SO4solutions. The catalytic activity inn-butane isomerization of these samples (at 300°C, 1 atm, and WHSV=2.5 h−1), previously activated in air at 620°C is not well correlated with their textural properties or the SO2−4concentration.Zr(OH)4samples calcined at temperatures higher than 375°C are crystalline and adsorb SO2−4groups, but which are not active catalytically. The catalytic activity decreases with the calcination temperature in a similar way as the OH groups (determined by chlorination) are eliminated, forming less reactive surface groups. When the crystalline samples are sulfated with H2SO4vapors, catalytically active materials are produced, irrespective of the crystalline state.The drastic sulfation overcomes the inertness of the crystalline surface and catalytic active sites forn-butane isomerization are produced. Thisin situresulfation may also compensate the sulfur losses during the reaction.