Low-temperature CO preferential oxidation in H2-rich stream over Indium modified Pd-Cu/Al2O3 catalyst

Abstract

The impact of Indium (In) doping upon the catalytic performance of Pd-Cu/Al₂O₃ for carbon monoxide preferential oxidation (CO-PROX) in hydrogen (H₂) rich atmosphere at low temperature has been studied. A series of catalysts with extremely low palladium (Pd) loading (0.06 wt%) are synthesized by the facile co-impregnation method. When the In/copper (Cu) atomic ratio equals 0.25, Pd-Cu-In_0.25/Al₂O₃ can keep 40% CO conversion and 100% carbon dioxide (CO₂) selectivity at least 120 min at 30 °C, which is significantly superior to the catalytic performance of Pd-Cu/Al₂O₃. The elaborate characterization findings reveal that the added In species to Pd-Cu/Al₂O₃ causes Indium oxide (In₂O₃) to generate, which produces the interaction of In₂O₃ with Pd-Cu/Al₂O₃, further promoting the dispersion of copper chloride hydroxide (Cu₂Cl(OH)₃). Moreover, the modification of In facilitates the re-oxidation of Pd⁰ to Pd⁺ through reducing the formation of palladium hydride (PdH_x) during the CO-PROX reaction. Meanwhile, the addition of In leads to the decrease of Cu⁺ electron cloud density, making it easier to be oxidized to Cu²⁺. Collectively, the easy re-oxidation of Pd⁰ and Cu⁺ is favorable to fulfill the Wacker cycle between Pd and Cu species, thus improving the catalytic performance for CO-PROX.

Keywords: Indium doping; Low-temperature CO preferential oxidation; Pd-Cu/Al(2)O(3).