CALORIMETRIC STUDY OF VANADIUM PENTOXIDE CATALYSTS USED IN THE REACTION OF ETHANE OXIDATIVE DEHYDROGENATION

Vanadium pentoxide catalysts have been studied in the partial oxidation reaction of ethane in the 723-843 K temperature range. The relationship between the acid-base properties and the catalytic behavior was investigated. The number and character of acidic sites of V2O5 catalysts were determined by studying the adsorption of a basic molecule using microcalorimetry. The reducibility level and the evolution of the surface state, as well as the heat evolved, were studied by using a pulse method with pure ethane only. The reaction of ethane oxidative dehydrogenation was studied by a continuous flow method and the activation energies for the formation of C2H4 and CO were calculated. The selectivity of the catalyst was interpreted in connection with the acid-base properties. The strong sites were observed to decrease rapidly with time on stream, although the catalysts were still active. Temperature-programmed reduction of V2O5 using a TG-DSC coupling was also investigated with hydrogen, ethylene, or ethane as reducers. The different heats of reduction are given. It was observed that C2H4 is a much more efficient reducing agent than H-2 and C2H6. Following each reduction, reoxidation studies by oxygen were performed in the same equipment showing clearly different steps in the reoxidation process.