Characterization of MoO3/TiO2–ZrO2 catalysts by XPS and other techniques

Abstract

To explore thermal stability of TiO2–ZrO2support, and dispersion and temperature stability of MoO3rTiO2–ZrO2 catalyst these systems were subjected to thermal treatments from 773 to 1073K and were examined by X-ray photoelectron spectroscopy, X-ray diffraction, and FT-infrared techniques. The TiO2–ZrO2mixed oxide support was obtained by a homogeneous coprecipitation method and MoO312 wt.%.was impregnated over the 773K calcined support by adopting a wet impregnation procedure. Characterization results suggest that the TiO2–ZrO2when calcined at 773K is in X-ray amorphous state and gets converted into a crystalline ZrTiO4compound beyond 873 K. The ZrTiO4compound is thermally quite stable up to 1073K calcination temperature in the absence of molybdena on its surface. In the case of MoO3/TiO2–ZrO2 catalyst, the molybdenum oxide is in highly dispersed state on the support surface when calcined at 773 K. However, above 773K calcination it selectively interacts with ZrO2portion of the TiO2–ZrO2 binary oxide and readily forms ZrMo2O8 compound by liberating TiO2. The ZrMo2O8 compound formation proceeds in a two-step process. In the first step, there is an incorporation of Mo6q ions into the ZrO2 oxide matrix and then the crystal growth occurs. The liberated TiO2 appears in the form of both anatase and rutile phases with varying intensities.