Surface and catalytic properties of triflic acid supported zirconia: Effect of zirconia tetragonal phase

In this paper, trifluoromethanesulfonic acid was successfully loaded over calcined crystalline zirconia. Zirconia was calcined at 200, 350, 500, 700 and 900 °C before trifluoromethanesulfonic acid was loaded. The catalysts were characterized by various sophisticated techniques such as FTIR, SEM, TEM, XRD and N2 adsorption-desorption measurements. The acidic behavior of the catalysts has been studied by nonaqueous potentiometric titration and FTIR spectra of adsorbed pyridine. The results showed that the catalysts are highly acidic and exhibited high catalytic activity in the esterification of acetic acid with benzyl alcohol (95%) with very high selectivity to benzyl ester (96%). Furthermore, the tetragonal phase of zirconia was the only phase up to 500 °C, and completely vanished at 900 °C. These changes in crystalline structure was also found to be related to the number and strength of acid sites. Our results showed that, the number and strength of acid sites were optimum at 350 °C, at which only tetragonal phase is the metastable one. Moreover, the catalysts were capable of recycling for five times without appreciable deactivation at 100 °C.