Catalytic activity of gold-perovskite catalysts in the oxidation of carbon monoxide

Perovskites (ABO₃ structures), which can be manipulated by partial substitution, are reported to be active supports for CO oxidation, but only at high temperatures, with no activity being shown for temperatures below 200?°C. In this study, these perovskites were investigated at low temperatures (below 100?°C) with improved activity found upon gold deposition. The presence of gold nanoparticles therefore significantly enhanced the catalytic activity, while the support itself was suspected to be involved in the reaction mechanism. A series of perovskites of the type ABO₃ (LaMnO₃, LaFeO₃, LaCoO₃, and LaCuO₃) were prepared using the citrate method, while the gold was deposited on them using the deposition-precipitation method. The supports were calcined at different temperatures for optimization. With the support calcined at 800?°C, the best catalyst was 1?wt% Au supported on LaFeO₃. Calcium-doping of this system showed decreased surface area, poorer crystallinity, and a drop in catalytic activity relative to the Au-LaFeO₃. In addition, Au-LaFeO₃ showed online stability over 21?h. Calcining the support improved the incorporation of gold nanoparticles into the perovskite lattice, resulting in superior catalytic activity. Nevertheless, at higher calcination temperatures, the catalytic activity of Au-CaTiO₃ was depressed while that of Au-LaFeO3 was enhanced. XPS revealed that in the active catalysts, both cationic and metallic gold coexisted, while in the inactive catalysts, the gold existed predominantly either as cationic or metallic gold.