Alkaline-earth-promoted Pd–Ag/Al2O3 for selective acetylene hydrogenation: green-oil mitigation, ethylene selectivity, and implications for hydrogen spillover

Removing trace acetylene from ethylene streams is critical to protect Ziegler-Natta polymerization. Eggshell Pd-Ag/θ-Al₂O₃ spheres (0.03 wt% Pd, 0.13 wt% Ag) were promoted with 1 wt% alkaline-earth additives to suppress green oil and improve ethylene selectivity. XRD, N₂ physisorption, H₂-TPR, NH₃/CO₂-TPD, TPO, SEM-EDS, and ICP-OES established structure-property links. Fixed-bed tests (10 bar, 40-60 °C) after H₂ prereduction showed promoter-stabilized θ-Al₂O₃, higher surface area and mesoporosity and stronger metal-support interactions. All promoted catalysts achieved ≳ 96% acetylene conversion with higher ethylene selectivity and reduced carbon deposition. A possible contribution from hydrogen spillover is discussed qualitatively based on indirect evidence.