A Comparison of the Reactivity of “Nonequilibrated” and “Equilibrated” V–P–O Catalysts: Structural Evolution, Surface Characterization, and Reactivity in the Selective Oxidation ofn-Butane andn-Pentane

• Published in: Journal of catalysis Vol. 160; no. 1; pp. 52 - 64
• Main Authors: Albonetti, S., Cavani, F., Trifirò, F., Venturoli, P., Calestani, G., López Granados, M., Fierro, J.L.G.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15.04.1996
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.1996.0123

Changes occurring on thermal treatment of the precursor of vanadium/phosphorus mixed oxide, the industrial catalyst for the oxidation ofn-butane, were studied. The precursor was mixed with stearic acid, used as an organic binder for pelletization of the powder. The calcination of the precursor leads to a partially oxidized compound, constituted of an amorphous VIV–P mixed oxide and a crystalline hydrated VV–P–O phase. The calcined compound, when left in a 1% hydrocarbon/air stream for 100 h leads to a “nonequilibrated” catalyst, and after 1000 h to the “equilibrated” catalyst. The catalytic activity of the nonequilibrated and equilibrated catalysts inn-butane andn-pentane oxidation was studied and compared; the chemical–physical features of the two catalysts were studied by means of XRD, FT-IR, chemical analysis, TGA, XPS, and TPD. Only well crystallized (VO)2P2O7was detected in the equilibrated catalyst and a homogeneous distribution of surface centers seems to be present on its surface. In the case of nonequilibrated catalyst, a poorly crystallized (VO)2P2O7is present together with an amorphous VIV–P–O phase and γ-VOPO4; these phases define a heterogeneous distribution of at least two kind of surface centers. This surface heterogeneity gives rise to a catalyst less selective inn-butane oxidation to maleic anhydride and less specific in the conversion ofn-pentane to phthalic anhydride.