Preparation, characterization and catalytic activity of tin oxide-supported 12-tungstophosphoric acid as a solid catalyst

Abstract

A series of solid acid catalysts were synthesized by incipient wetness impregnation method by varying the wt% of 12-tungstophosphoric acid (TPA) on tin oxide. The prepared catalysts were characterized by thermal analysis, XRD, FT-IR and BET surface area. The acidity of the catalyst was measured by different techniques. The suitability of the materials was studied for acid-catalyzed esterification reaction using acetic acid and amyl alcohol. The acidity measurements showed that the total acidity increases with the rise of TPA content up to 20 wt% (monolayer coverage) and decreases thereafter. FT-IR spectra of pyridine adsorbed on the catalysts showed the presence of both Brønsted and Lewis acidities. Material with 20 wt% TPA on tin oxide having high surface area and acid sites acts as the better catalyst for esterification reaction. For the material that exhibits the optimum catalytic activity, selective poisoning of the potential catalytic centers revealed that Brønsted sites play the major role in carrying out the reaction. The straight-line plots of −ln(1-ester formed) versus catalyst weights support that the esterification reaction obeys first-order kinetics. The reusability study justifies that the catalyst is stable and active.