Acid Promoter-Modified Cs/Al<sub>2</sub>O<sub>3</sub> Catalyst for Methyl Methacrylate Production by Aldol Condensation of Methyl Propionate with Formaldehyde
Lin Xu, Xiaoping Wang, Jianhua Song, Jichang Liu, Dianhua Liu
Abstract
Methyl methacrylate (MMA) is frequently produced via the aldol condensation process involving methyl propionate (MP) and formaldehyde (FA), which is believed to be an intriguing and effective approach. Here, acid–base bifunctional catalysts were developed, and a strategy combining Cs with various acid promoters on an Al 2 O 3 support was proposed to enhance catalytic activity and stability. Experimental results demonstrated that the Cs–Nb combination exhibited the highest catalytic performance because of its optimal distribution of acid–base sites. A relationship between the activity of the catalyst and the acid–base properties was identified. Likewise, the Cs–Nb/Al 2 O 3 catalyst under optimal loading exhibited the maximum MMA yield owing to the highest density of medium acid sites. Moreover, a plausible acid–base synergetic reaction pathway for MMA synthesis over the Cs–Nb/Al 2 O 3 catalyst was proposed. Lower activity was observed on the Cs–Nb/Al 2 O 3 catalyst due to carbonaceous deposition during the reaction. However, heat treatment in the atmosphere at 400 °C can readily revive the activity of the catalyst, demonstrating remarkable reusability.