Influence of textural properties and trace water on the reactivity and deactivation of reconstructed layered hydroxide catalysts for transesterification of tributyrin with methanol

Magnesium–aluminum hydrotalcites with a Mg/Al molar ratio of 2 were prepared by coprecipitation or by urea hydrolysis. The as-prepared samples, as well as their activated analogues, were characterized by N2 physisorption, phenol chemisorption, SEM, XRD, TGA, and DRIFTS. The base-catalyzed transesterification of tributyrin with methanol at 333 K was used to probe the reactivity of the materials. The reconstructed hydrotalcite samples exhibited much higher catalytic activity than the mixed oxides of Mg and Al. Nevertheless, the turnover frequency for the reaction was about two orders of magnitude lower than that of homogeneous sodium methoxide. Variations in the textural properties of the reconstructed hydrotalcite catalysts did not significantly affect the surface base site density or the turnover rate of transesterification. However, the presence of trace water not only enhanced the transesterification reaction rate but also led to severe catalyst deactivation. Characterization of deactivated catalysts revealed a replacement of the interlayer Brønsted base sites with butyric anions, which led to an expansion of the interlayer distance.