Improved catalytic performance and stability of defected UiO-66-SO3H in the esterification reaction of cyclohexene with cyclohexanecarboxylic acid

The preparation of cyclohexanol by indirect hydration of cyclohexene is divided into two steps. Firstly, cyclohexene is esterified with formic acid, and then the resulted cyclohexyl formate is hydrolyzed to obtain cyclohexanol and formic acid. The key step in this process is the acid-catalyzed esterification reaction. Because formic acid had a great destructive effect on the structure of metal organic frameworks catalysts, cyclohexanecarboxylic acid was selected to replace formic acid in the esterification of cyclohexene in this work. Cyclohexanecarboxylic acid is relatively weak in polarity and acidity, and the molecular size of which is relatively large, therefore, a catalyst with abundant acid content and suitable pore size distribution needs to be constructed. The sulfonic acid functionalized UiO-66-SO3Hdef material containing lattice defects was prepared using acetic acid as the modulator, UiO-66 and UiO-66-SO3H without lattice defects were also prepared for comparison, and the samples were characterized by various methods. The acid content and acid strength of the UiO-66-SO3Hdef material were significantly increased, a greater proportion of mesoporous structure was obtained from the resulting defects sites. Compared to UiO-66 and UiO-66-SO3H, which were inactive in the esterification reaction of cyclohexene and cyclohexanecarboxylic acid, the UiO-66-SO3Hdef material had a significant improvement in its catalytic performance. The conversion rate of cyclohexene was up to 50.54%, and the selectivity of cyclohexyl carboxylate was 86.56%. After five times of reuse, the catalytic performance had no significant decrease, and the structure of the recovered catalyst remained unchanged.

Automated summary

In this study, a sulfonic acid functionalized UiO-66-SO3Hdef material with lattice defects was used as a catalyst, and significant improvement in catalytic performance was achieved in the esterification reaction of cyclohexene. The catalyst exhibited high conversion rate and selectivity. The research results indicate that constructing a catalyst with abundant acid content and suitable pore size distribution is crucial for this reaction process.