Unveiling the Role of Ga- and Cr-Based Catalysts in CO2-Assisted Oxidative Dehydrogenation of Propane: Mechanistic and Support-Acid/Base Perspectives

Propylene (C3H6) is a vital building block in the chemical industry as it serves as a key raw material for producing plastics, synthetic fibers and numerous daily-use chemicals. However, the current production routes of C3H6 are energy-intensive and face sustainability challenges, prompting the scientific community to explore alternative technologies for its production. The oxidative dehydrogenation of propane (ODHP) using CO2 as a soft oxidant offers a safe and sustainable pathway for C3H6 production, where CO2 can act as a hydrogen scavenger, coke suppressor and site re-activator. Gallium- and chromium-based catalysts are among the most studied systems for CO2-assisted ODHP, yet they operate by distinct mechanisms: Ga catalysts follow pathways where both acidic and basic sites are involved, while Cr catalysts rely on redox cycles involving variations in the oxidation state of chromium. In addition to performance and reaction mechanism, Ga- and Cr-based catalysts differ markedly in terms of sustainability, with Cr systems facing environmental and regulatory challenges associated with Cr6+ species toxicity, while Ga systems, although less toxic, are constrained by gallium scarcity and cost. This review compares Ga- and Cr-based catalysts side by side, emphasizing how support effects, addition of promoters and mechanistic insights fine tune their performance. The aim is to highlight the advantages, the limitations as well as the sustainability implications of these materials and finally to outline future directions for designing more efficient and environmentally friendly catalysts for propylene production.