n-Butane oxidation using catalysts prepared by treatment of VOPO4· 2H2O with octanol

Abstract

The preparation of vanadium phosphorus oxide butane oxidation catalysts from the reaction of VOPO₄· 2H₂O with octan-1-ol, octan-2-ol and octan-3-ol is described and discussed. In these preparations the alcohol acts as a reducing agent forming octanal, octan-2-one or octan-3-one and a V^IV catalyst precursor compound. Use of octan-1-ol and octan-2-ol leads to the formation of VOHPO₄· 0.5H₂O but with distinctly different morphologies for the two alcohols. VOHPO₄· 0.5H₂O from octan-1-ol comprises thin platelets which are transformed, under the reaction conditions (367 °C, 1.5 %n-butane in air), topotactically to (VO)₂P₂O₇ with a high surface area (31 m² g^–1) and a high catalytic activity. The material derived from octan-2-ol exhibits thicker platelets that result in a final catalyst with a lower surface area (7 m² g^–1) and poorer catalytic performance. Use of octan-3-ol leads to the formation of VO(H₂PO₄)₂, exclusively. Under reaction conditions this is transformed to VO(PO₃)₂ with a low surface area (2 m² g^–1) which exhibits a high selectivity for the oxidation of n-butane to maleic anhydride without the formation of any carbon oxides as by-products. The origin of this high selectivity is discussed in terms of the isolation of the active sites on the catalyst surface owing to the presence of an excess surface phosphorus concentration.