Characterization of supported Vanadium oxide catalysts by low temperature oxygen chemisorption technique: I. The V 2O 5/γ-Al 2O 3 system

Abstract

Low temperature oxygen chemisorption (LTOC) has been applied to characterize γ-Al 2O 3 supported vanadium oxide catalysts. The results strongly suggest the formation of a monolayer with high dispersion of V-oxide on the alumina surface. The monolayer coverage of the surface is completed when the V 2O 5 content of the catalysts reach 11.9% and beyond this loading crystallites of V 2O 5 start to form on the alumina surface. Within the monolayer level the active surface area and active site density are found to increase with increased vanadia loading, while those in the ‘post monolayer’ region show a sharp decline as the load increases. The dispersion of vanadia remains essentially constant within the monolayer level and decreases almost linearly as a function of V 2O 5 loading in the post monolayer region. Information gathered from other techniques, including ESR, IR and surface area measurements, substantiate the results of LTOC experiments. Thus, LTOC technique is found to be a valuable tool for characterizing supported oxidation catalysts which are identified with redox properties.