Synthesis of silica supported AuCu nanoparticle catalysts and the effects of pretreatment conditions for the CO oxidation reaction

Supported gold nanoparticles have generated an immense interest in the field of catalysis due to their extremely high reactivity and selectivity. Recently, alloy nanoparticles of gold have received a lot of attention due to their enhanced catalytic properties. Here we report the synthesis of silica supported AuCu nanoparticles through the conversion of supported Au nanoparticles in a solution of Cu(C₂H₃O₂) ₂ at 300 °C. The AuCu alloy structure was confirmed through powder XRD (which indicated a weakly ordered alloy phase), XANES, and EXAFS. It was also shown that heating the AuCu/SiO₂ in an O₂ atmosphere segregated the catalyst into a Au-CuO_x heterostructure between 150 °C to 240 °C. Heating the catalyst in H₂ at 300 °C reduced the CuO_x back to Cu⁰ to reform the AuCu alloy phase. It was found that the AuCu/SiO₂ catalysts were inactive for CO oxidation. However, various pretreatment conditions were required to form a highly active and stable Au-CuO_x/SiO₂ catalyst to achieve 100% CO conversion below room-temperature. This is explained by the in situ FTIR result, which shows that CO molecules can be chemisorbed and activated only on the Au-CuO_x/SiO₂ catalyst but not on the AuCu/SiO₂ catalyst.