Oxidative Dehydrogenation of Ethane andn-Butane on VO_x/Al₂O₃Catalysts

Author： Blasco T. Galli A. López Nieto J.M. Trifiró F.

ISSN： 0021-9517

Source： Journal of Catalysis, Vol.169, Iss.1, 1997-07, pp. : 203-211

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Abstract

γ-Al₂O₃-supported vanadium oxide catalysts (0–6.3 wt% V atoms) were prepared, characterized, and tested for the oxidative dehydrogenation (ODH) of both ethane andn-butane. The vanadium loading strongly influences the catalytic behavior of γ-Al₂O₃-supported vanadium oxide catalysts during the ODH ofn-butane and ethane. While the catalytic activity in the ODH reactions increases with the vanadium loading, the selectivity to the corresponding olefins shows a maximum for catalysts with 3–4 wt% V atoms. In addition, the selectivity to oxydehydrogenation products during the ODH of butane was lower than the selectivity to ethene during the ODH of ethane. Associated VO₄tetrahedra were observed by⁵¹V-NMR on catalysts with V loading lower than 5 wt%, while VO₆octahedra were predominant on catalysts with higher V loading. In this way, although catalysts with octahedral V⁵⁺species show higher catalytic activity, higher selectivity to oxydehydrogenation reactions was achieved on catalysts in which mainly tetrahedral V⁵⁺species were observed. The number and nature of the acid sites also change with the vanadium loading. Thus, Lewis acid sites were observed mainly on catalysts with low V loading, while both Lewis and Brønsted acid sites were observed on catalysts with high V loading. Although V⁵⁺species were observed mainly on calcined samples, V⁴⁺species are observed on tested catalysts and their concentration depends on the alkane conversions used in the catalytic tests.