Molecular structure and reactivity of vanadia-based catalysts for propane oxidative dehydrogenation studied by in situ Raman spectroscopy and catalytic activity measurements

• Published in: Journal of catalysis 2004-03, Vol.222 (2), p.293-306
• Main Authors: Christodoulakis, Antonios, Machli, Maria, Lemonidou, Angeliki A, Boghosian, Soghomon
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Exact sciences and technology; General and physical chemistry; Oxidative dehydrogenation; Propane; Raman spectroscopy; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Titania; Vanadia catalysts; Zirconia
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2003.10.007

The effect of support (ZrO 2 and TiO 2) and vanadia loading (1.2–10 wt%) on the molecular structure and the catalytic performance in propane oxidative dehydrogenation (ODH) were investigated using in situ Raman spectroscopy and catalytic activity measurements. In situ Raman spectra under oxidizing, reducing, and steady-state ODH reaction atmospheres were obtained for the studied catalysts. The main differences between the structure of VO x entities in the two supporting materials derive from variations in the vanadia dispersion, which appears to be better in the case of the V 2O 5/TiO 2 compared to that of V 2O 5/ZrO 2 at the same VO x density. In situ Raman spectra recorded in the presence of water vapor revealed that VO x species are stable at high temperature while at low temperature the surface of the catalysts becomes hydrated. Significant perturbations of all kinds of VO bonds were observed under reduction with propane and reaction conditions at 500 °C. The reactivity studies revealed that under the same reaction conditions oxidative dehydrogenation rates expressed per V atom are influenced by the type of the specific support and are functions of the VO x density. The ability of vanadium to activate the CH bond weakens with increasing VO x density, whereby the number of VO M ( M= support metal atom) bonds per V is reduced due to incorporation of vanadium in formation of VOV bridges. The combination of the results obtained from the in situ Raman spectra and the catalytic activity measurements points to a significance of VO–support bonds in the kinetically significant reaction steps.