Three-dimensional ordered macroporous HPW/titania–alumina catalysts for catalytic oxidative desulfurization of fuels

Abstract

A series of three-dimensionally ordered macroporous (3DOM) alumina doped phosphotungstic acid (HPW)/TiO2 materials was synthesized successfully through sol–gel method with highly ordered 3D polystyrene monoliths as macroporous template. The characterization results of scanning electron microscope and transmission electron microscopy upheld the existence of periodically arranged macroporous structure. The infrared spectroscopy and powder X-ray diffraction results confirmed the homogeneous distribution of Keggin-type HPW on Al2O3–TiO2 matrix. Furthermore, the scanning electron microscopy-energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy, and inductively coupled plasma spectrometer measurements proved the introduction of alumina element on the TiO2 framework. NH3 temperature-programmed desorption (NH3-TPD) and pyridine-IR investigation characterized the effects of alumina modification on the surface acidity and acidic sites of catalysts. The 3DOM alumina doped HPW/TiO2 nanocomposites were applied in the catalytic oxidation desulfurization process. The alumina doped HPW/TiO2 catalyst showed superior catalytic oxidation desulfurization performance than corresponding 3DOM HPW/TiO2 catalyst, mesoporpus alumina doped HPW/TiO2, and microporous alumina doped HPW/TiO2. 99.7% of benzothiophene (DBT) in the model fuel could be removed within 1 h under optimized conditions. This should be attributed to the common influence of 3DOM structure and appropriate alumina addition amount on HPW/TiO2 composite, which further improved mass diffusion of DBT and its derivatives on the pore channel and the adsorption process on the catalyst surface, respectively. Moreover, the as-prepared catalyst displayed excellent cycle stability with a slight decrease in catalytic performance even after six runs.