Copper-zinc oxide and ceria promoted copper-zinc oxide as highly active catalysts for low temperature oxidation of carbon monoxide

摘要

Copper-zinc oxide catalyst is prepared by co-precipitation technique. The effects of aging the precipitate in the parent solution and addition of CeO2 are investigated. CuO-ZnO catalyst containing 60% CuO and 40% ZnO is found to be active for the ambient temperature oxidation of CO; however the activity can be improved considerably by aging the catalyst during the precipitation process. Alternatively, the catalyst activity can be improved by the addition Of CeO2 during the precipitation without aging the precipitate. A much higher CO oxidation activity is achieved for the CuO-ZnO catalyst system than that reported earlier for the same system. X-ray photoelectron spectra (XPS) and XRD results show that aging the catalyst during the precipitation process brings out more ZnO to the surface leading to higher CuO dispersion. This leads to the formation of relatively less crystalline or amorphous CuO that promotes the formation of more linear or weakly bonded CO on the catalyst surface as well as the creation of CuOx species under redox conditions. The metastable copper oxide species is a good electrophilic reagent with superior oxygen transfer capacity and the presence of weakly bonded surface CO ensures a low temperature oxidation activity for the catalyst. It is further seen that addition of ceria to the catalyst also brings out similar advantages. However, increase in the CeO2 content increases the CO bonding strength causing an increase in the light-off temperature (loss of low temperature oxidation activity), in spite of high overall reducibility and CO adsorption capacity of the catalyst. The reducibility and susceptibility to variation in the oxidation states of copper oxide are critical to the activity of the catalyst. It is also found that addition of CeO2 brings out a significant improvement in the catalyst stability over an extended reaction period as well as at elevated reaction temperature. (c) 2006 Elsevier B.V. All rights reserved.