Si-Modified Cs/Al<sub>2</sub>O<sub>3</sub> for Aldol Condensation of Methyl Acetate with Formaldehyde to Methyl Acrylate by Chemical Liquid Deposition
Zhenyu Wu, Taolue Sun, Zengxi Li, Chunshan Li
Abstract
SiO2-modified γ-Al2O3 by chemical liquid deposition (CLD) was developed as a catalyst support for use in the aldol condensation of methyl acetate with formaldehyde to produce methyl acrylate. Cs/Al2O3 and Cs/Si–Al2O3 catalysts synthesized by incipient-wetness impregnation were characterized, and catalytic performance was evaluated. A correlation between structural features and acid–base properties has been established, and the effect of SiO2 deposition was investigated. The amount of strong acid sites was reduced, and the Brønsted acid sites were introduced onto the surface of Al2O3 with the deposition of SiO2. Moreover, interaction of Cs with the Brønsted acid sites generates the surface Si–O–Cs species which served to enhance selectivity to methyl acrylate. Conversion of methyl acetate was increased due to the formation of new basic sites following Cs incorporation. An excess of SiO2 and Cs hampered decomposition of the cesium nitrate, resulting in strong acid site formation and lower product yield. A 10Cs/1.2Si–Al2O3 composition has been established as optimal with a 4.8 times higher product yield in comparison with 10Cs/Al2O3. Lower activity in the case of the 10Cs/1.2Si–Al2O3 catalyst can be associated with carbon deposition during the reaction; activity can be regenerated after heat treatment at 400 °C.