In Situ Temperature-Programmed Diffuse Reflectance Infrared Fourier Transform Spectroscopy (TPDRIFTS) of V2O5/TiO2 Catalysts

Abstract

Temperature-programmed diffuse reflectance infrared Fourier transform spectroscopy (TPDRIFTS) is proposed to follow in situ temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) experiments of catalytic systems, as a method for observing relationships between the surface structure and the reducibility of the catalyst under the actual reaction conditions. TPDRIFTS studies of desorption and reduction of a conventional V2O5/TiO2 catalyst have been carried out, showing the presence in both processes of four stages. Both desorption and reduction experiments result in similar DRIFTS spectra for temperatures below 400 °C, accounting for two processes: (1) water desorption and (2) condensation of highly dispersed vanadium species in between V2O5 islands on the anatase surface. V2O5 reduction by H2 takes place between 400 and 680 °C, being characterized by elimination of the first-overtone bands of V= O groups. DRIFTS is shown to be a very powerful tool to characterize both hydrogen-consuming and nonconsuming processes such as O= migration above 725 °C (stage IV). Relationships between the area of V = O overtones bands obtained by TPDRIFTS and the oxidation state of vanadium are proposed as a method to estimate this parameter under actual reaction conditions.