Effect of nature and surface density of oxygen species on product distribution in the oxidative dehydrogenation of propane over oxide catalysts

Catalytic performance of non-reducible (rare-earth/alkaline-earth oxides) and reducible (vanadium-based oxides) metal oxides in auto-thermal oxidative dehydrogenation (ODH) of propane differs strongly regarding to the ratio of C3H6/C2H4. In contrast to the latter materials, ethylene is the main olefin over the former ones. In order to elucidate factors influencing the catalytic performance, a kinetic analysis of the oxidative dehydrogenation (ODH) of propane was performed. In this analysis, the ODH reaction is assumed to occur via formation and further transformations of free propyl radicals. It was demonstrated that the overall reaction rate of these both processes is affected by both strength and density (surface concentration) of oxidising active sites. However, the ratio of propene-to-ethylene is mostly affected by the density of oxidising sites (DOS), and to much less extent by their strength. High DOS is essential for further ODH of propyl radicals to propene and, therefore, for suppression of concurrent cracking reaction channel yielding ethylene.