Hydroxyl-Directed Anchoring and Electronic Structure of Pt–Sn on γ-Al2O3 for Propane Dehydrogenation

Although γ-Al2O3-supported Pt–Sn catalysts are central to industrial propane dehydrogenation (PDH), conventional support design has primarily focused on structural properties, largely overlooking the role of surface hydroxyl chemistry in governing metal–support interactions. Here, we show that the distribution of surface hydroxyl types strongly affects Pt–Sn anchoring, particle growth, and performance of the catalyst supported on γ-Al2O3. By hydrothermally tailoring AlOOH precursors and exploiting a topotactic phase transition, three γ-Al2O3 supports (Al2O3-AIP, Al2O3-NP, and Al2O3-NF) with distinct distributions of terminal μ1-OH and doubly bridged μ2-OH sites were prepared. Systematic characterization showed that the hydroxyl-rich Al2O3-NP and Al2O3-NF supports produced substantially smaller Pt–Sn particles than Al2O3-AIP. Spectroscopic trends suggest preferential involvement of acidic μ1-OH sites at lower precursor loadings and progressively greater involvement of μ2-OH sites as the μ1-OH sites approached saturation. The μ2-OH-enriched surfaces favored precursor anchoring associated with highly dispersed Pt–Sn clusters (∼0.6 nm) after reduction. In propane dehydrogenation at 580 °C, the μ2-OH-enriched 0.5Pt–1.3Sn/Al2O3-NF catalyst achieved an initial propane conversion of 60% while maintaining a propylene selectivity above 97%. Site-occupancy experiments and C3H6-DRIFTS further suggest that precursor anchoring involving μ2-OH sites is associated with improved Pt–Sn dispersion and weaker propylene adsorption. These results show that controlling surface hydroxyl types can regulate metal anchoring and particle growth in Al2O3-supported dehydrogenation catalysts.