The Role of Acid Base and Redox Features in the Catalytic Behavior of Vanadium Phosphorus Oxygen Formulations

LAURA CORNAGLIA, EDUARDO LOMBARDO

STUDIES IN SURFACE SCIENCE AND CATALYSIS

Elsevier

Año: 1994 vol. 90 p. 429 - 440

0167-2991

The role played by bulk VOPO, phases, surface V(v) centers and LewislBronsted acidsites in defining the catalytic behavior of VPO formulations is discussed in terms of theinformation provided by a battery of spectroscopic techniques. All selective catalysts for theoxidation of n-butane to maleic anhydride only show the diffraction patterns of vanadylpyrophosphate. Through 31P MAS NMR and Raman spectroscopy it is possible though, todetect the presence of small amounts of VOPO, phases in the used solids but the bestcatalysts are those containing traces of V(v) phases. V(v) centers are detected through XPSon the surface of fresh and used catalysts but their concentration does not correlate withcatalytic performance. The existence of Lewis and Bronsted acid sites has beendocumented through the adsorption of basic probe molecules whose fate was followed byFTlR spectroscopy. Very strong Lewis and Bronsted acid sites play key roles in the paraffinactivation as well as in the rates of oxygen insertionlhydrogen abstraction on the furan-likeintermediates. The data analyzed here also provide new insight on the structural changesoccurring in the catalyst during the first few hundred hours on stream as well as the role ofthese modifications in the reaction mechanism and catalytic performance.