IN-SITU TEMPERATURE-PROGRAMMED DIFFUSE-REFLECTANCE INFRARED FOURIER-TRANSFORM SPECTROSCOPY (TPDRIFTS) OF V2O5 TIO2 CATALYSTS/

Temperature-programmed diffuse reflectance infrared Fourier transform spectroscopy (TPDRIFTS) is proposed to follow in situ temperature-prog rammed reduction (TPR) and temperature-programmed desorption (TPD) exp eriments of catalytic systems, as a method for observing relationships between the surface structure and the reducibility of the catalyst un der the actual reaction conditions. TPDRIFTS studies of desorption and reduction of a conv entional V2O5TiO2 catalyst have been carried out, showing the presence in both processes of four stages. Both desorptio n and reduction experiments result in similar DRIFTS spectra for tempe ratures below 400 degrees C, accounting for two processes: (1) water d esorption and (2) condensation of highly dispersed vanadium species in between V2O5 islands on the anatase surface. V2O5 reduction by H-2 ta kes place between 400 and 680 degrees C, being characterized by elimin ation of the first-overtone bands of V=O groups. DRIFTS is shown to be a very powerful tool to characterize both hydrogen-consuming and nonc onsuming processes such as O- migration above 725 degrees C (stage IV) . Relationships between the area of V=O overtones bands obtained by TP DRIFTS and the oxidation state of vanadium are proposed as a method to estimate this parameter under actual reaction conditions.