Silicotungstic acid/zirconia immobilized on SBA-15 for esterifications

Abstract

A simple wet-impregnation method and controlled calcination process was used for preparing nano-sized silicotungstic acid (STA) supported on zirconia embedded inside the various mesoporous silicas such as SBA-15, MCM-41 and MCM-48. Catalysts with different (%) STA loadings were also synthesized and characterized by XRD, N 2 adsorption–desorption, TEM, 29Si-MAS NMR, FT-Raman spectroscopic techniques. The acidic behavior of the catalysts was studied by TPD of ammonia and FT-IR pyridine adsorption technique. The effect of calcination temperature on the textural parameters of the catalysts and the integrity of STA on the surface of the catalyst were also examined. Moreover, the performance of these catalysts was investigated in the esterification of isoamyl alcohol (IAA) with acetic acid (AA). Catalytic activities were correlated with the acidity of the catalysts. Effects of reaction parameters such as mole ratio of reactants, reaction temperature, catalyst concentration and reusability of the catalyst were studied to get higher substrate conversions and product selectivities. Among the catalysts, 15 wt.% STA/22.4 wt.% ZrO 2/SBA-15 calcined at 1123 K was found to be the most active and acidic catalyst, showing higher conversion and selectivity than neat 15 wt.% STA/ZrO 2 in esterification of IAA by AA. The reaction was found to be heterogeneously catalyzed and no contribution from homogeneous (leached) STA into the medium under the reaction conditions was observed.