Optimization of Cr/SBA-15 Catalysts for CO₂-Assisted Oxidative Dehydrogenation of Propane to Propylene

Cr/SBA-15 catalysts were optimized for CO₂-assisted oxidative dehydrogenation of propane (ODH-CO₂) using a Taguchi L9(3³) design spanning temperature (550–650°C), Cr loading (5–10 wt %), and W/F (0.010–0.020 g min mL⁻¹). Signal-to-noise analysis and ANOVA ranked factor importance as temperature ≫ W/F > Cr loading. The confirmation run at 600°C, 7 wt % Cr, and W/F = 0.015 achieved 37.1% propane conversion with 84.0% propylene selectivity. Characterization linked this window to an intermediate loading that preserved SBA-15 mesostructural order and maximized redox-accessible chromate species. XANES linear-combination fitting showed that the 7 wt % catalyst retained a higher Cr⁶⁺ fraction in both fresh and spent states than the 5 or 10 wt % analogues, while H₂-TPR revealed the largest reducible population at 7 wt %. The catalytic and spectroscopic evidence supports a Mars–van Krevelen mechanism operating on dispersed Cr⁶⁺=O sites, with CO₂ re-oxidizing reduced Cr to sustain selective ODH. At higher temperatures and/or loadings, increased reduction and aggregation shifted products toward cracking and deep oxidation. Integration of DOE with spectroscopy thus identified an intermediate Cr loading/contact-time regime on SBA-15 that optimized redox selectivity and enhanced process-relevant performance in CO₂-assisted ODH of propane.