Improved activity and stability in CO oxidation of bimetallic Au–Cu/TiO2 catalysts prepared by deposition–precipitation with urea

Au-Cu bimetallic catalysts supported on TiO2 were prepared for the first time by sequential deposition-precipitation with the urea method, copper first then gold. Au-Cu catalysts with four different Au:Cu atomic ratios were synthesized (1:0.4 to 1:1.2). This method allowed quantitative deposition of both copper and gold and the formation of small metal particles. Characterization by TPR and by DRIFTS coupled with CO adsorption showed that when the samples were activated in air at 300 °C gold was present in metallic form, copper in the form of an oxide, and Au and Cu were in interaction, probably forming a Au/CuO/TiO2 system. When the catalysts were activated in hydrogen at 300 °C, the metal particles were smaller (2 nm) and bimetallic. The activation of Au-Cu catalysts in air at 300 °C produced more active catalysts than the activation under hydrogen at the same temperature. However, whatever the activation procedure, the highest catalytic activity in CO oxidation was obtained for the catalyst with an Au:Cu ratio of 1:0.9. This calcined catalyst also presented a TOF almost 3 times higher and a better temporal stability than monometallic gold catalysts in the reaction of CO oxidation at 20 °C. Compared to monometallic catalysts, the better catalytic results obtained with calcined Au-Cu/TiO2 indicate a promoting effect between gold and copper oxide in the reaction of CO oxidation.