Esterification over rare earth oxide and alumina promoted SO42−/ZrO2

Solid superacid catalysts including SO42−/ZrO2 (SZ), rare earth (RE) oxide-promoted SZ and RE oxides together with alumina-promoted SZ were prepared. Their catalytic performances in the esterification reaction of ethanol and acetic acid were investigated. The textural property, crystalline phase and surface acidity of the prepared catalysts were characterized by using nitrogen adsorption–desorption isotherms, X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy of pyridine adsorption techniques, respectively. Effects of the reaction time and catalyst reuse cycle as well as catalyst regeneration on the catalytic behaviors were studied. Experimental results showed that Yb2O3–Al2O3 promoted SZ (designated as SZAY) catalyst exhibited an optimal esterification performance; the Lewis acid sites with moderate and super strong strength could mainly be responsible for the esterification reaction; and doping both Yb2O3 and Al2O3 on SZ not only boosted the esterification activity but also alleviated catalyst deactivation resulted from the surface sulfur loss by solvation.