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

Abstract

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, consistent with 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, with propane and CO2 conversions of 11.5% and 5.5%, 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 lower conversion at 280 min and poor catalytic stability, with similar propylene selectivity. 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 valorizes waste from water-treatment and promotes the CO2 valorization through the CO2-ODHP reaction.

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