Synergistic effect in the CO2-oxidative dehydrogenation of propane to propylene over IrPt catalysts supported on mesoporous Mg-SBA-15

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The effect of partial Pt substitution by Ir on the propylene formation via CO 2 -oxidative dehydrogenation of propane (CO 2 -ODH) has been investigated. To decrease coke formation, the synthetized Pt, Ir and PtIr catalysts were supported on mesoporous silica (SBA-15) modified with Mg (∼2.9 wt%). The best propylene production was archived with the PtIrMg-1.5 catalyst showing a highest degree of Pt substitution with Ir (Pt/Ir at a ratio of 1.5). Characterization of the catalyst by various techniques (ICP-OES, XRD, FTIR of adsorbed pyridine, XPS and HRTEM) showed that partial substitution of Pt by Ir influences the nature of the surface acid sites and leads to easier reduction of Pt 2+ species. The catalyst efficiency toward propane formation from CO 2 follows the trend: PtIrMg-1.5 > PtIrMg-4 > PtMg > IrMg. The highest propylene selectivity exhibited IrMg catalyst showing the lowest propane conversion. It was found that propane conversion decreases lineally with increasing Brønsted acidity and increases with increasing Lewis-to-Brønsted acidity ratio. The synergy effect observed in reaction over PtIrMg-1.5 catalyst was attributed to the cumulative effects of its lowest Brønsted acidity, largest Ir content, Pt-Ir alloy formation and the stabilizing effect of the MgO nanoparticles decorating support surface.