Selective catalytic reduction of NO_x with NH_3 over cerium-tungsten-titanium mixed oxide catalyst: Synergistic promotional effect of H_2O_2 and Ce~(4+)

摘要

A highly active catalyst of cerium-tungsten-titanium mixed oxide was synthesized by introducing Ce~(4+) and H_2O_2 in the base sample of Ce_(20)W_(10)Ti_(100)O_z-Ce~(3+). As a consequence, the NH_3-SCR activity of Ce_(20)W_(10)Ti_(100)O_z-Ce~(3+) is significantly improved as the additives of Ce~(4+) and H_2O_2 enlarge the Brunauer-Emmett-Teller (BET) surface area by refining its pore size. Meanwhile, the introduction of Ce~(4+) increases the Lewis acid sites of Ce_(20)W_(10)Ti_(100)O_z-Ce~(3+) and decreases its low-temperature Brønsted acid sites. The further addition of H_2O_2 improves the Brønsted acid sites and dispersion of cerium/tungsten species, and thereby enhances the concentrations of the adsorbed oxygen (O_α) and the adsorbed oxygen (O'_α) due to the activation of chemisorbed water on the surface of the catalyst. The addition of Ce~(4+) and H_2O_2 shows a synergistic promotional effect, which is due to the largest BET surface area and the highest concentrations of O_α or/and O'_α. Ce_(20)W_(10)Ti_(100)O_z-Ce~(3+):Ce~(4+) = 17.5:2.5 + H_2O_2 exhibits the highest catalytic activity compared with the conventional ones (Fig. 5).