Additive-free synthesis of robust monolithic mesoporous silica support used in catalysis

Abstract

Use of mesoporous silica as functional material or as support in adsorption and catalysis has been very limited in commercial terms due to limitations of powder morphology and accompanied handling and recycling issues. Previous reports on preparations of monolithic mesoporous silica generally indicate complicated procedures and/or deterioration of final structure. In this research, a simple scalable one-pot sol-gel synthesis with subsequent free atmospheric evaporation is applied to prepare monolithic mesoporous silica (of MSU family). Effects of synthesis parameters such as reagent concentrations and additives on both nano-structure and physical stability of the monolith were investigated. No-additive synthesis resulted in the most robust monolith under mechanical handling and hydrodynamic conditions. Material's disintegration rate in agitated water was as low as 0.1 mg/h and its structural stability was approved under hydrothermal conditions. The monolithic mesoporous silica samples functionalized with acid and base surface groups were used independently in catalytic esterification and transesterification reactions. At relatively low temperatures (~ 50 °C), conversion of stearic acid to ethyl stearate was completed in the presence of monolithic acid catalyst. At the same conditions, above 50% and 20% conversions of triacetin to ethyl acetate (as a typical biodiesel production method) were achieved in the presence of monolithic acid and base catalysts respectively.