Structural characterization and catalytic activity of molybdenum oxide supported zirconia catalysts

A series of MoO3/ZrO2 catalysts with different molybdenum content of 5–30 wt.% MoO3 were prepared by impregnation method. The prepared catalysts were calcined at 400, 550, 700, 800, and 1000 °C. The structural characteristics were investigated by means of thermal analysis (DTA and TGA), powder X-ray diffraction (XRD) while the textural properties was determined from low temperatures adsorption of N2 at −196 °C. The surface acidity was measured with nonaqueous titration of n-butylamine in acetonitrile. The catalytic activity was tested by cumene dealkylation and ethanol conversion using the microcatalytic pulse technique.XRD reveals that the samples contain mixture of tetragonal and monoclinic zirconia phases. At low MoO3 loading, i.e. <15 wt.% MoO3, MoO3 was not detected. When the loading of MoO3 exceeds 15 wt.%, crystalline MoO3 and Zr(MoO4)2 were formed, particularly for the higher calcination temperature products. The incorporation of MoO3 into ZrO2 enhanced the surface acidity of the catalysts. It was found that the surface acidity gradually increased as the temperature of thermal treatment was increased from 400 to 550 °C and also with the molybdenum oxide content.This increase in the surface acidity was correlated with the degrees of crystallinity of the samples. The surface area was found to increase with increasing of MoO3 up to 15 wt.%. Further increase of MoO3 beyond 15 wt.% led to a decrease of N2-SBET. The catalytic activity was strongly influenced with the textural, structural properties and surface acidities of the catalysts investigated.