Investigation of different modifiers for nanocrystal zirconia on W/ZrO 2 catalysts via esterification

Abstract

The present work focused on investigation of different modifiers, such as Si, Al, Bi, and Pb on the tungstated zirconia catalysts. First, the different modifier precursors were introduced onto the nanocrystal zirconia having molar ratio (metal: Zr) at 0.01:1. Then, the 15 wt% of tungsten (W) was impregnated onto the modified zirconia. The physicochemical properties influenced by the modifiers were determined using the N 2 physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and electron spin resonance (ESR). In order to measure the catalytic activity, esterification of acetic acid and 1-heptanol was performed. It was found that the modifiers apparently resulted in dramatically decreased activity due to decreased acidity of the catalysts. It can be proposed that the modifiers had three major roles; (i) inhibit the phase transformation, (ii) enhance the presence of F-center (electrons stabilized in oxygen vacancy), and (iii) increase strong interaction of adsorbed species on zirconia. The third effect was the key factor leading to pronounced decrease in acidity of the catalysts.