Relevant articles and documents
Surface dynamics of a vanadyl pyrophosphate catalyst for n-butane oxidation to maleic anhydride: An in situ Raman and reactivity study of the effect of the P/V atomic ratio
Cavani, Fabrizio Luciani, Silvia Esposti, Elisa Degli Cortelli, Carlotta Leanza, Roberto
This work focused on investigating the effect of the P/V atomic ratio in vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride, on the nature of the catalytically active phase. Structural transformations occurring on the catalyst surface were investigated by means of in situ Raman spectroscopy in a non-reactive atmosphere, as well as by means of steady-state and non-steady-state reactivity tests, in response to changes in the reaction temperature. It was found that the nature of the catalyst surface is affected by the P/V atomic ratio even in the case of small changes in this parameter. With the catalyst having P/V equal to the stoichiometric value, a surface layer made of α-VOPO4 developed in the temperature interval 340400°C in the presence of air; this catalyst gave a very low selectivity to maleic anhydride in the intermediate T range (340-400°C). However, at 400440°C δ-VOPO4 overlayers formed; at these conditions, the catalyst was moderately active but selective to maleic anhydride. With the catalyst containing a slight excess of P, the ratio offering the optimal catalytic performance, δVOPO4 was the prevailing species over the entire temperature range investigated (340-440°C). Analogies and differences between the two samples were also confirmed by reactivity tests carried out after in situ removal and reintegration of P. These facts explain why the industrial catalyst for n-butane oxidation holds a slight excess of P; they also explain discrepancies registered in the literature about the nature of the active layer in vanadyl pyrophosphate.
Structure Sensitivity of the Catalytic Oxidation of n-Butane to Maleic Anhydride
Cavani, Fabrizio Centi, Gabriele Trifiro, Ferruccio
Disorder along the (020) cleavage plane of the (VO)2P2O7 catalyst considerably enhances the activity of the selective oxidation of n-butane to maleic anhydride.
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