Characteristic of gallium and boron modified ZrO2 on W/ZrO2 catalysts for esterification

Abstract

The solvothermal and precipitation methods were used for the preparation of zirconia (ZrO2). Then, the ZrO2 supports were impregnated with tungsten (VI) chloride to obtain W/ZrO2 catalyst. It was found that the spherical shape and dense mass in solvolthermal sample and irregular roughness shape particle in precipitation method were obtained. The XRD results of W/ZrO2 presented the monoclinic, tetragonal zirconia and WO3 crystalline for both preparation methods, which can be confirmed with the raman spectroscopy. The resulting catalysts exhibited good dispersion of WOx species as surface polytungstates on these catalysts and also have agglomeration of WO3 together with polytungstate. The BET surface area of precipitation method was the highest and affected on high catalytic performance on esterification. For the Ga modification from GaNO3 with 0.5wt% and 1wt% on the zirconia support, the morphology was not changed after impregnation. The surface area and surface acidity of the Ga-modified zirconia support was higher than the unmodified one. The catalyst having 1 wt% of Ga with precipitation method (W/ZrO2_1%Ga_pre) also gave high catalytic performance. For the B modification from HBO3 with 0.5wt% and 1wt% on the zirconia support, the surface acidity and BET surface of the zirconia are higher after impregnation with boron. However, the results after impregnated with tungsten showed the opposite trend. With boron loading the activity and surface acidity decreased than the unmodified one, affecting by the two preparation methods. The possible reason may be the small atomic size of boron is able to interact with tungsten resulting in the decreased surface acidity.