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.

Graphical Abstract

中文翻译：

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酸性质不同的煅烧和未煅烧TiO 2 -ZrO 2上环戊酮的自缩合

研究了煅烧和未煅烧的TiO ₂ -ZrO ₂上环戊酮的自缩合。通过XRD，FTIR，SEM，N ₂吸附-脱附和吡啶FTIR考察了催化剂的性能。与煅烧的TiO相比₂ -ZrO ₂，未煅烧的TiO ₂ -ZrO ₂显示出优异的催化性能（环戊酮和二聚物的产率为86％的94％转化率）。这可能是因为未煅烧的TiO ₂ -ZrO ₂既有刘易斯和质子酸，而煅烧的TiO ₂ -ZrO ₂仅包含路易斯酸。动力学分析表明，CC偶联是两种催化剂上的限速步骤。对于未煅烧的TiO ₂ -ZrO ₂，催化剂表面上两种物质之间发生了C-C偶联。通过氢键，布朗斯台德酸位点将环戊酮牢固地吸附在催化剂表面，然后烯醇中间体会攻击相邻的路易斯酸位点极化的另一种环戊酮。结果，布朗斯台德酸和路易斯酸在催化剂中的共存在环戊酮自缩合反应中显示出增强的活性。

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