Abstract
The CaO/HMCM-22 catalysts were prepared by an ultrasonic impregnation method and their catalytic performances in Knoevenagel condensation were investigated. The characterization results of XRD, SEM, and TPD showed that no significant structural change of MCM-22 was observed after modification by CaO with ultrasonic assistance. Ultrasonic cavitation could reduce the agglomeration between particles and improve the dispersion of CaO on the surface. With the increase of CaO loading, the strength and content of base increased, and the strength of strong acid decreased, while the amount of weak acid sites increased slightly. The catalytic performance of CaO/HMCM-22 prepared by ultrasonic impregnation is better than that of CaO/NaMCM-22 and HMCM-22 for Knoevenagel condensation reactions, which indicates that the catalysts possess both acidic and basic sites after modification. Consequently, the acid–base bifunctional catalysts prepared by the ultrasonic impregnation method maintained high catalytic activity and have improved reusability. Compared with the conventional impregnation method, the strategy developed here is simple and efficient.
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