CO2-assisted oxidative propane dehydrogenation over vanadium supported on ferric sludge: the role of Fe–V interactions in redox behavior and stability

Ferric sludge from a drinking water treatment plant, was valorized as a catalyst support for the propane dehydrogenation reaction. Vanadium was incorporated at loadings of 4 wt% (highly dispersed VOx species), 8 wt% (small V2O5 crystallites) and 16 wt.% (large V2O5 crystallites and mixed Al-V-O species) and evaluated in CO2-assisted oxidative dehydrogenation of propane (CO2-ODHP). The results showed that vanadium incorporation markedly enhanced the propane and CO2 conversion compared to the non-oxidative direct dehydrogenation of propane (DHP) reaction. The superior catalytic performance was attributed to the predominance of monomeric VOx species, which strengthened Fe–V interactions, suppressed excessive reduction of the active phases, and enhanced oxygen mobility. Taking together, these effects promoted a balanced redox cycle by favoring the partial Fe reduction and increasing the lattice oxygen mobility, as evidenced by XPS analysis. As a result, the catalyst containing 4 wt.% V exhibited good stability, achieving propylene and ethylene selectivities of 80.8% and 19.2%, respectively, after 280 min on stream. In contrast, higher vanadium loadings (8-16 wt.%) favor the formation of polymeric VOx domains and crystalline V2O5 phases, resulting in a slight decrease in catalytic performance, especially propylene selectivity, and poor catalytic stability. CO2-ODHP conducted on monomeric VOx species supported on an inexpensive high surface area waste material yields a fairly stable catalyst for propylene production. This approach offers a doble environmental benefit: it valorize waste from water-treatment and promotes the CO2 valorization through the CO2-ODHP reaction.