(583fr) Nanosized Au/CuO-TiO2 Catalysts for CO Oxidation At Low Temperature

Carbon monoxide is harmful to human beings when its concentration reaches 35 ppm in air. CO is a toxic, colorless and tasteless gas; it is produced by the fuel without complete oxidation. The most extensively studied reaction in the history of heterogeneous catalysis is becoming increasingly important in the context of cleaning air and lower automotive emissions. The reaction is important for environment protection. When gold is deposited as nanoparticles on metal oxides, it exhibits surprisingly high catalytic activity for CO oxidation at a temperature as low as -73 ^oC. The activity of gold catalysts also depends on support, preparation method and condition. The promoters were added in Au/TiO₂ to change the support properties, including electronic effect and geometric effect. The effects of promoter such as CuO was investigated. The support was prepared by incipient-wetness impregnation with aqueous solution of nitrate salt. TiO₂ was from Evonik-Degussa Company (P-25). Au catalysts were prepared by deposition-precipitation (DP) method at pH value of 7 and 65 ^oC. The catalysts were characterized by inductively-coupled plasma-mass spectrometry, temperature programming reduction X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The reaction was carried out in a fixed bed reactor with a feed containing 1% CO in air at WHSV of 120,000 ml/h g. High gold dispersion and narrow size distribution was obtained by DP method. The different contents of Cu were added in Au/TiO₂, which enhanced the activity on CO oxidation significantly. Au/5% CuO_x-TiO₂ was the best catalyst among all the catalysts. Cu was in amorphous state which could stabilize the Au nanoparticles. Cu was in Au⁺¹ state. Cu also could donate partial electrons to Au. Besides, Cu could create the lattice oxygen vacancy in TiO₂ structure, which is beneficial to activity. In conclusion, the highly active Au/CuO_x-TiO₂ catalysts were developed. The interactions among Au, Cu⁺¹ and TiO₂ account for the high catalytic activity for CO oxidation. The significant promotional effect of Cu on CO oxidation at low temperature was demonstrated.