Nb^sub 2^O^sub 5^/SBA-15 catalyzed propanoic acid esterification

A family of niobia (Nb2O5) functionalized SBA-15 solid catalysts have been prepared via wet impregnation with NbCl5 (2-32 wt% Nb) and subsequent thermal processing, for application in the acid catalyzed esterification of propanoic acid with methanol. Bulk and surface physicochemical characterization revealed that highly dispersed niobia species present at low loadings when calcined at 500 °C exhibit strong Brönsted acid character and associated activity for esterification. Increased calcination temperatures are found to result in a decrease in Brönsted:Lewis acid ratio associated with recrystallization of the niobia phase leading to a loss of catalyst activity. Esterification activity is found to be directly proportional to Brönsted:Lewis acid ratio, with the 2 wt% Nb/SBA-15 catalyst pre-calcined at 500 °C found to exhibit highest activity and excellent reusability without deactivation.