Promotional effect of tungsten-doped CeO2/TiO2 for selective catalytic reduction of NOx with ammonia

Abstract

We examined the effects that the physicochemical properties of Ce/Me/Ti catalysts had on the selective catalytic reduction (SCR) activity after various metals (W, Mo, and La) were added to non-vanadium-based catalysts in order to improve NH3–SCR activity. We studied the properties of the catalysts through the use of physiochemical techniques, including Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) transmission infrared spectroscopy (IR), and inductively coupled plasma optic emission spectroscopy (ICP). The catalytic activity tests of the Ce/Ti catalysts with various ceria loadings revealed that the Ce/Ti with 10wt.% ceria (10Ce/Ti) exhibited excellent activity. Thus, various metals were added to the 10Ce/Ti. The tungsten-doped 10Ce/Ti catalyst exhibited the highest activity (10Ce/W/Ti: Ce was deposited after tungsten had been deposited on TiO2). We investigated the correlation between the catalyst's Ce valence state and its activity. Different Ce3+ ratios were observed when various metals were added to Ce/Ti. The highest Ce3+ ratio was observed in 10Ce/W/Ti at 0.3027, and the catalyst efficiency had a positive correlation with higher Ce3+ ratios. The SCR activity was found to increase as the Ce3+ ratio increased when tungsten was added to 10Ce/W/Ti. Furthermore, in the case of 10Ce/W/Ti, it seemed that the Brønsted acid sites were more abundant relative to those on 10Ce/Ti. Upon the injection of SO2 in the SCR reaction, 10Ce/Ti was rapidly deactivated. However, the 10Ce/W/Ti catalyst exhibited an excellent resistance to SO2-induced deactivation relative to 10Ce/Ti. Thus, the addition of tungsten to Ce/Ti resulted in excellent NOx conversion and SO2 resistance.