The Cyclopentanone Self-condensation Over Calcined and Uncalcined TiO2–ZrO2 with Different Acidic Properties

Abstract

The self-condensation of cyclopentanone has been studied over calcined and uncalcined TiO₂–ZrO₂. The catalyst properties were examined by XRD, FTIR, SEM, N₂ adsorption–desorption, and pyridine FTIR. Compared with calcined TiO₂–ZrO₂, uncalcined TiO₂–ZrO₂ exhibited superior catalytic performance (94% conversion of cyclopentanone and 86% yield of dimer). This might be because uncalcined TiO₂–ZrO₂ has both Lewis and Brønsted acids, while calcined TiO₂–ZrO₂ only contains Lewis acids. Kinetics analysis indicated that C–C coupling was the rate-limiting step on the two catalysts. For uncalcined TiO₂–ZrO₂, the C–C coupling occurred between the two species on the catalyst surface. Through the H bond, the cyclopentanone was firmly adsorbed on the catalyst surface by Brønsted acid sites, then the enol intermediate could attack another cyclopentanone polarized by adjacent Lewis acid sites. As a consequence, the coexistence of Brønsted and Lewis acids in catalysts exhibited enhanced activity in cyclopentanone self-condensation.