MultiTRACK and operando Raman-GC study of oxidative dehydrogenation of propane over alumina-supported vanadium oxide catalysts

Combined operando Raman-GC and MultiTRACK studies provide new insights into the interaction of propane with a V/alumina catalyst. The Raman-GC analysis showed that the catalyst is essentially in the oxidized state during oxidative dehydrogenation reaction conditions, while stable intermediates and/ or carbonaceous deposits are not observed on the catalyst surface. In the absence of oxygen, the catalyst is reduced by propane, and two types of carbonaceous deposits can be observed: one with a more aliphatic character at low temperatures, and one with a graphitic character at higher temperatures, of which the particle size increases as a function of increasing temperature. In agreement with the Raman studies, evidence for carbonaceous deposits was also provided by the MultiTRACK experiments. From CO₂ response profiles of the oxidation of these deposits, it was concluded that increasing temperature of operation and increasing propane/oxygen ratio enhance the amount and stability of the surface carbonaceous species formed. Based on the MultiTRACK studies also the participation of two types of oxygen species in the reaction of propane was evident: a highly reactive super-surface oxygen mainly yielding CO₂, and a catalytic oxygen, associated with the vanadia phase. In MultiTRACK conditions, the extent of participation of vanadia-associated oxygen increases with reaction temperature and/or the propane/oxygen ratio, enhancing the selectivity of the reaction to propene.