Effects of morphology and crystal phase of sulfated nano-titania solid acids on catalytic esterification

Abstract

In this work, sulfated TiO2 nanostructures with different morphology structures and anatase/rutile phase ratios were synthesized by a hydrothermal method followed by calcination. The nanotube, nanorod and nanoparticle morphologies were obtained by varying the hydrothermal and/or annealing temperatures, and the anatase/rutile phase ratio was adjusted by controlling the annealing temperature. The characterization indicated well dispersed bidentate SO4 2− linked to the TiO2 surface. The catalytic activity of the synthesized sample was evaluated by the esterification of acetic acid with n-butanol. It was shown that the prepared sulfated titania possessed different catalytic activity. Effects of different reaction conditions were discussed. The catalytic activity was dominated by the concentration of surface acid sites of the catalyst. Hence, with the help of TEM, SEM, XRD and BET analyses, the concentration of surface acid sites per unit area of sulfated TiO2 was correlated with the type of morphology and increased linearly with the rutile phase content. The nanoparticle morphology and high rutile phase ratio were favorable for the catalytic activity per unit area of sulfated TiO2 in our experiments.