Design of transition metal catalysts for CO₂-enabled oxidative dehydrogenation of propane to propylene

This thesis investigates the rational design of transition-metal catalysts for the CO₂-enabled oxidative dehydrogenation of propane (CO₂-ODHP), an emerging strategy that combines the mitigation of greenhouse gas emissions with the sustainable production of propylene, a key platform chemical. The work addresses the thermodynamic and kinetic constraints of conventional propane dehydrogenation by employing CO₂ as a soft oxidant, thereby coupling dehydrogenation with the reverse water-gas shift reaction (RWGS) to enhance selectivity, suppress coke formation, and valorize CO₂. The experimental program focuses on Ga-, Cr-, Pt-, and Ce-containing catalysts supported on γ-Al₂O₃, synthesized through incipient wetness impregnation in three distinct sequences [(a) simultaneous impregnation of Ce and Pt followed by Ga; (b) co-impregnation of Ga and Ce followed by Pt; (c) sequential impregnation of Ga, then Ce, and finally Pt, with drying and calcination after each step] to elucidate the effect of metal deposition order. After catalytic results indicated that synthesis route (a) provided the most effective formulation, an additional catalyst was prepared by replacing gallium with chromium while maintaining identical loadings and conditions, in order to evaluate the influence of changing the active phase. A comprehensive set of physicochemical characterizations (XRD, BET, NH₃-TPD, CO₂-TPD, XPS) is applied to probe surface area, porosity, acidity, basicity, and oxidation states, enabling correlation of structure-function relationships. Catalytic tests were performed in a fixed-bed quartz reactor at 620 °C for 280 min, using propane/CO₂/He feed mixtures. The results demonstrate that impregnation sequence critically influences acid-base balance, redox cycling, and active phase dispersion. The findings advance understanding of CO₂-assisted oxidative pathways and offer guidelines for tailoring multifunctional catalysts capable of bridging CO₂ utilization with olefin production.