Methylammonium-FAU zeolite: Investigation of the basic sites in base catalyzed reactions and its performance

The basicity of methylammonium-faujasite zeolites (FAU) was evaluated in the Knoevenagel and Claisen–Schmidt condensation reactions and in the alcoholysis of propylene oxide with methanol. The basic character of FAU zeolites (Y zeolite with Si/Al=2.5Si/Al=2.5 and X zeolite with Si/Al=1.4Si/Al=1.4) was systematically altered by incorporating cesium and methylammonium cations, which were located in charge compensation sites. In all three reactions, methylammonium-FAU zeolites showed higher specific activity in comparison to cesium-FAU, indicating that these catalysts encompass stronger basic sites. Characterization of the zeolites has shown that ion exchange of sodium by methylammonium cations reduces their micropore volume, however enhances the strength of their basic sites. TPD-CO2 experiments demonstrated that aluminum rich zeolites possess higher basicity due to higher number of sites. Additionally, XPS (O1s) measurements illustrated that when monomethylammonium cation is present in ion exchange sites, structural zeolite oxygen anions have a higher basic character in comparison to cesium-FAU. This unique result opens news perspectives for application of these highly basic and low-cost methylammonium molecular sieves in base-catalyzed reactions such as Knoevenagel, Claisen–Schmidt condensation and nucleophilic cleavage of propylene oxide with methanol.