Silicotungstic acid supported zirconia: An effective catalyst for esterification reaction

A series of solid acid catalysts were synthesized by incipient wetness impregnation method by varying the wt% of silicotungstic acid on hydrous zirconia (ZSTA). The prepared catalysts were characterized by PXRD, FTIR, UV–vis DRS, EPMA, BET surface area, acid sites, etc. FTIR and UV–vis DRS studies indicate that the material retain the Keggin-type structure of silicotungstic acid up to 500 °C. The suitability of the materials was studied for acid catalysed esterification reactions using formic, acetic, propionic, n-butyric acid and n-butyl alcohol (NBA), isobutyl alcohol (IBA) and sec-butyl alcohol (SBA). Material with 15 wt% STA on hydrous zirconia having high surface area and acid sites acts as better catalyst for esterification reactions. The esterification of acids with NBA was found to be higher than IBA and SBA. In all the cases, the selectivity for the corresponding esters is nearly100%. The straight-line plot of −ln(1 − conversion) versus reaction time for the reactions carried out at 98 °C supports that the esterification reaction obeys first order kinetics with respect to acid concentration. The reusability study justifies that the catalyst is stable and active.

The esterification of acetic acid with various alcohols is an electrophilic substitution reaction, catalysed by strong Brϕnsted acid sites. The influence of reaction time on the acetic acid conversion was given above using 15 wt% ZSTA as catalyst (0.025 g). A gradual rise in the conversion was seen with increase in duration of the reaction period. As seen from figure, in 4 h of reaction time, 91.5% of conversion is obtained, where as at the end of 5 h only 92% of the reaction is complete.Figure optionsDownload as PowerPoint slide