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

The self-condensation of cyclopentanone has been studied over calcined and uncalcined TiO2-ZrO2. The catalyst properties were examined by XRD, FTIR, SEM, N-2 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 BrOnsted 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 BrOnsted acid sites, then the enol intermediate could attack another cyclopentanone polarized by adjacent Lewis acid sites. As a consequence, the coexistence of BrOnsted and Lewis acids in catalysts exhibited enhanced activity in cyclopentanone self-condensation.