Morphology and Catalytic Application of Homogeneous Nano-composite Oxides Containing Titania

Abstract

A series of mixed oxide supports consisting of TiO2 and Cr2O3 or Fe2O3 with different wt% of Cr2O3 or Fe2O3 (5–20 wt%) were prepared by two methods: precipitation and impregnation. The catalysts containing MoO3 and NiO were prepared by successive impregnation with the appropriate amounts of ammonium heptamolybdate and nickel nitrate on the calcined support to obtain catalysts with 8.0 wt% MoO3 and 3.0 wt% NiO. The surface areas (SBET), the pore volumes, and the average pore diameters were measured by nitrogen adsorption method; all catalysts containing MoO3 and NiO have surface areas less than the pure supports due to the blocking of some pores by Mo and/or Ni ions leading to a decrease in the total pore volume of these catalysts. The structures of the samples have been investigated by powder X-ray diffraction (XRD) and differential thermal analysis (DTA). The results showed that the mixed oxide samples containing Cr2O3 or Fe2O3 were nanosized particles, and they existed as an amorphous phase in the samples. The investigation by infrared spectroscopy (FT-IR) indicated that there were interactions between Cr2O3 or Fe2O3 and TiO2 in the mixed oxide. The prepared samples were purposively used as the supports for hydrodesulfurization (HDS) process. The sulfided catalysts were tested in the HDS reaction of thiophene, and the results showed that the highest thiophene HDS conversion in this system requires an optimum content of Cr2O3 or Fe2O3 in the mixed oxide support, which is considered as 10 wt% in this study. Nevertheless, the way of incorporation has significant effects on catalytic activity.