Carbonate Inhibition in Au-Cu/γ-Al₂O₃ Catalysts for CO Oxidation

Incorporating Cu into gold-based catalysts effectively reduced nanoparticle sintering and free carbonate accumulation, promoting long-term preservation of catalytic surface area over time. This study explores the catalytic activity of monometallic Au and bimetallic AuCu catalysts with varying Au:Cu atomic ratios (1:0.5, 1:1, and 1:1.5) that were synthesized on $\gamma$-Al${}_2$O${}_3$ via sequential deposition–precipitation with urea. The catalysts were pretreated in either air or H${}_2$ and evaluated for CO oxidation activity and stability. A comprehensive characterization (EDS, BET, TEM, H${}_2$-TPR, O${}_2$-TPO, XPS, DRIFTS, and UV–Vis) was used to investigate particle size, metal oxidation states, and redox properties. Among all materials, the AuCu 1:1 catalyst exhibited the highest low-temperature CO conversion (>90% at 0 ${}^{\circ }$C) and improved stability during 24 h tests, reflecting minimal nanoparticle sintering as confirmed by TEM analysis. In situ DRIFTS revealed that the presence of Cu${}^{+}$ and Cu${}^{2+}$ minimizes the accumulation of free carbonates (one of the main deactivation pathways in Au/$\gamma$-Al${}_2$O${}_3$) while promoting the formation of reactive intermediates that facilitate CO${}_2$ production. Notably, air pretreatment at moderate temperature proved as effective as H${}_2$ pretreatment in activating both monometallic and bimetallic catalysts. These findings highlight the role of Cu as a structural and electronic promoter of gold, offering practical guidelines for designing durable, cost-effective catalysts for low-temperature CO oxidation on non-reducible supports.