Abstract
Abstract XRD, LRS, XPS, TPR and ESR have been used to investigate the dispersion and reduction behavior of copper oxide in CuO/CeO 2 /TiO 2 samples (copper oxide supported on ceria-modified anatase). The results indicate that: (1) ceria can be highly dispersed on the surface of TiO 2 support, and corresponding to a dispersion capacity (DC) of about 6.98 Ce 4+ ions/nm 2 TiO 2 ; (2) the dispersion of copper oxide on ceria-modified TiO 2 is below the loading amount of ceria. For the samples with ceria loading prior to 6.98 Ce 4+ ions/nm 2 TiO 2 , the dispersion of copper oxide decreases with the ceria loading. When the loading of ceria is greater than 6.98 Ce 4+ ions/nm 2 TiO 2 , the dispersion of copper oxide increases with ceria loading; (3) the reduction behavior of the copper oxide species are also shown to be correlated to the ceria loading. For CuO/CeO 2 /TiO 2 samples with the low ceria loading of 3 wt.%, the dispersed copper oxide species could be simply regarded as two species (Cu–I and Cu–II) according to the differences in the reduction behavior. For the high ceria loading CuO/CeO 2 /TiO 2 samples, e.g. ceria loading amount of 40 wt.%, the TPR profiles indicate that the reduction behavior of copper oxide is similar to that in CuO/CeO 2 system, and the sample should be approximately regarded as the composition of two systems, CuO/CeO 2 and CeO 2 /TiO 2 . In addition, the activities of the catalysts, CuO/TiO 2 , CuO/CeO 2 /TiO 2 and CuO/CeO 2 , in the NO+CO reaction at different temperatures have been studied to monitor the relationship between the catalytic activity versus the composition of the catalysts. For the samples with low copper oxide loading, the catalytic activity varies as in this order: 4Cu–6Ce–Ti 2 2 ≈4Cu–40Ce–Ti, which suggests that the dispersed ceria species hinder the activity of surface copper species in 4Cu–6Ce–Ti sample. While for the samples with high ceria loading, the activities of copper species are greatly enhanced due to the formation of crystalline CeO 2 . Furthermore, for the CuO/CeO 2 /TiO 2 samples, especially for that with lower copper oxide and ceria loadings, the dispersion states of the copper and ceria are also discussed by the consideration of incorporation model proposed previously [Catal. Lett. 12 (1992) 51].
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