Synergistic Catalysis by MgO Induced Acid‐Base Bifunctional Sites for Cross Condensation of HCHO and Acetaldehyde

Abstract

Acid‐base synergistic catalysis greatly enhances the performance of MgO‐based catalysts in the Aldol condensation. Here, the effect of acid‐base strength/concentration/proportion and the synergistic catalysis on the performance of cross condensation between HCHO and acetaldehyde were studied. The NH3/CO2‐TPD results suggested that weak acidic sites combined with medium basic sites were beneficial for the cross condensation. The loading of MgO nanocrystals on SiO2 induced the generation of new acidic sites (Mg‐O‐Si). Combined with the inherent basic sites (Mg‐O‐Mg) and Mg‐O‐Si, the acid‐base bifunctions sites could catalyse the cross condensation of HCHO and acetaldehyde synergistically. The appropriate proportion of acidic/basic sites (10/1) is critical for the cross condensation in the presence of vast water in formalin. The effect of reaction parameters, including the molar ratio of substrates, reaction temperature, liner velocity and weight hourly space velocity, were investigated for the cross condensation. The results showed that 10 wt% MgO/SiO2 catalyst possessed the highest catalytic activity (57.9% conversion of acetaldehyde and 84.3% selectivity of acrolein) under the optimal reaction parameters among the investigated catalysts. The MgO/SiO2 can be reused and recovered its catalytic performance after in‐situ regeneration in air to remove the carbon deposition.