A series of M/TiO 2 and M/TiO 2 -SiO 2 (with M = Mn, Cu and Ce) catalysts were prepared by adopting a wetimpregnation method and investigated for the selective catalytic reduction (SCR) of NO x in the temperature range of 100-500 o C with excess (10 vol.%) oxygen in the feed at industrially relevant conditions. Our XRD results suggest that the growth of crystalline TiO 2 phase is strongly inhibited due to the SiO 2 migration into the TiO 2 lattice. The increase of SiO 2 molar content in TiO 2 -SiO 2 support led to the decrease in anatase phase of titania peak intensity of XRD spectrum and also exhibiting a lower crystallinity of TiO 2 with no phase transition of anatase to rutile. Our XPS depth profile analysis illustrate that the surface atomic ratio of Cu 1+ / Cu 2+ greatly enhanced with increase in TiO 2 content in the TiO 2 -SiO 2 support, and these results are consistent with the H 2 -TPR results where the additional reduction peak evolved at 200 o C for copper loaded titania-rich (Cu/TiO 2 ) catalyst. The high activity of Cu-based TiO 2 formulations has been assigned to the enhancement in the formation of Cu 1+ active sites, existence of surface Cu 2+ , Cu 1+ species and the increment of reduction potentials of surface copper species. The Ce 3+ / Ce 4+ and Ce 3+ /Ce n+ atomic ratio (1.14 and 0.53, respectively) in Ce/TiO 2 catalyst calculated from deconvoluted XPS spectra are much higher than that of Ce/TiO 2 -SiO 2 (1:1) and Ce/TiO 2 -SiO 2 (3:1). The existence of higher Ce 3+ surface species over CeO 2 /TiO 2 illustrates the increment of surface oxygen vacancies and thus facilitates for the adsorption of oxygen species or activates reactants in the SCR reaction. The relative atomic percentage value of Mn 4+ /Mn 3+ characterized by deconvoluted XPS was significantly high (Mn 4+ /Mn 3+ = 1.98) for the Mn/TiO 2 compared to Mn/TiO 2 -SiO 2 catalysts (Mn 4+ /Mn 3+ = 1.23, 1.75). When ceria was supported on pure TiO 2 , the low-temperature reduction peak was broad and less defined, and the reducibility in the low temperature range was much less pronounced. On the other hand, the addition of ceria to titania with strong reciprocal interaction is generally perceived as a shift in the bulk reduction temperature to lower values, to about 500-650 °C. As bigger Ce 4+ ions enter the lattice structure to proxy the Ti 4+ ions with smaller ionic radii (2.48 and 2.15 Å, respectively), the lattice could become highly strained. The NO x conversions and the apparent kinetic constant of the catalyst k ac , over the Cu, Mn, Ce-loaded on different supports TiO 2 and TiO 2 -SiO 2 (3:1 and 1:1) catalysts measured under steady-state conditions results demonstrated higher activity of the Ti-rich materials.

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