Incorporation of one or dual Brønsted acidic sites within the mesopores of MCM-41: Synthesis and catalytic activity in acetalization reaction

Abstract

In recent years, various kinds of heterogeneous acid catalysts have been prepared and utilized for different catalytic applications. Among them, designing the easily recoverable catalysts containing two distinct Brønsted acidic sites with enhanced catalytic properties is promising. In this work, modification of the mesopores of MCM-41 as a siliceous solid support with two suitable nitrogen-containing amino- and piperazine-propylsilyl groups followed by covalent interaction with 1,4-butane sultone introduced sulfonic acid groups to this mesoporous material. The additional electrostatic interaction with phosphotungstic acid groups generated the second acidic sites on ammonium and piperazinium moieties. The successful synthesis of these solid acid catalysts was confirmed by FT-IR, energy dispersive X-ray (EDX), and inductively coupled plasma optical emission (ICP-OES) spectroscopies; CHN elemental analysis; nitrogen sorption; and XRD techniques. The catalytic experiments in benzaldehyde acetalization with ethylene glycol resulted in moderate to high activity from 76% to 97% within 2 h. Moreover, the higher catalytic activity was related to the one possessing two kinds of acidic sites due to the synergistic effect between these acidic sites.