Effect of CO pretreatment on the performance of CuO/CeO 2/γ-Al 2O 3 catalysts in CO + O 2 reactions

Abstract

The influence of CO pretreatment on the properties of CuO/CeO 2/γ-Al 2O 3 catalysts was investigated using X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The activities of the treated catalysts were measured in low-temperature CO oxidation reactions (≤200 °C). For this reaction, the activities of CuO/CeO 2/γ-Al 2O 3 catalysts are intimately related to operation temperature, copper oxide loading amount and CO pretreatment. The influence of the first two factors, i.e., operation temperature and copper oxide loading amount, is similar to the previous results of CuO/γ-Al 2O 3 catalysts [H.Q. Wan, Z. Wang, J. Zhu, X.W. Li, B. Liu, F. Gao, L. Dong, Y. Chen, Appl. Catal. B: Environ. 79 (2008) 254–261]. CO conversions are clearly promoted with increasing operation temperatures and the maximum CO conversions are always reached over the catalysts with a copper oxide loading amount of 0.6 mmol Cu 2+/100 m 2 γ-Al 2O 3, at the set operation temperatures. For the third factor, CO conversions over the CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts are slightly lower than those over the fresh catalysts with the same amount of copper oxide. In contrast, the activity was enhanced over the CO-treated CuO/γ-Al 2O 3 catalysts in the previous report. XRD, TPR and XPS results show that CO pretreatment at 250 °C mainly results in the reduction of crystalline CuO to Cu 0 and of partially dispersed Cu 2+ to Cu + and Cu 0 in CuO/CeO 2/γ-Al 2O 3 catalysts. IR results indicate that besides the CO–Cu + adsorption band at ∼2110 cm −1 on the fresh and CO-pretreated catalysts exposed to CO stream when temperatures are above 50 °C, a new adsorption band at 2170 cm −1 is detectable corresponding to CO–Cu 2+ or CO–Cu 0 over the CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts with copper oxide loading amounts of 0.3 and 1.2 mmol/100 m 2γ-Al 2O 3 at the adsorption temperatures beyond 150 °C. The influences of the ceria modification on the generation of copper species in fresh and CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts and their activities in CO oxidation were discussed.