CaO/HMCM-22 zeolite catalysts were prepared by ultrasonic impregnation and characterized by XRD

N2 physical adsorption-desorption

SEM

FT-IR

NH3-TPD and CO2-TPD. The structure of MCM-22 zeolite still remained after CaO modification with ultrasonic assistance. Ultrasonic cavitation could reduce the agglomeration between particles

improve the dispersion of CaO on the surface of zeolite and increase the accessible catalytic active sites. By increasing CaO loading

the strength and content of base increased

while the strength of strong acid decreased significantly and the amount of weak acidic sites increased slightly. Knoevenagel condensation reactions were conducted over the synthesized catalysts. The strategy developed here showed excellent catalytic performance for this reaction compared with the conventional impregnation method and the conversion of benzaldehyde reached 88.3% under optimal ultrasonic irradiation within 2 h reaction. The catalytic performance of CaO/HMCM-22 was better than that of HMCM-22 and CaO/NaMCM-22

resulting in good catalytic activity for Knoevenagel condensation reactions and obvious acid-base synergetic effects. The reusability of the synthesized catalysts with ultrasonic assistance was also investigated. Obvious improvment was achieved and conversion of benzaldehyde was above 65% after being reused 5 times.