Three-dimensionally ordered macroporous Ce-W-Nb oxide catalysts for selective catalytic reduction of NO with NH3

Abstract

• Ce-W catalyst is optimized by combining Nb-modification and structural manipulation. • 3DOM structure provides abundant diffusion channels for catalytic reactions. • 3DOM structure ensures the high dispersion of active components. • Synergistic effect among the species of Ce, Nb and W promotes the increase of O α . • Active NH 3 and NO x species are increased over 3DOM Ce-W-Nb catalysts. A string of 3DOM Ce-W-Nb ternary catalysts for NH 3 -SCR were prepared by a colloidal template method. The 3DOM Ce-W-Nb 0.15 catalyst had the best SCR activity and yielded more than 90% NO conversion at 275 ∼ 450 °C in the high GHSV of 120,000 h −1 . In addition, it exhibited good tolerance to H 2 O and SO 2 . The addition of Nb increased the number of active sites and made them dispersed more evenly, optimized the pore structure to a certain extent, and increased the specific surface area. The interaction among Ce, W, and Nb species promoted the increase of chemisorbed oxygen and enhanced the redox properties, thus contributing to the satisfactory SCR activity at low temperatures. In addition, the synergistic effect between Nb and W provided sufficient Lewis acid sites for the 3DOM Ce-W-Nb x catalyst, which was conducive to the good SCR performance at high temperatures. The NH 3 -SCR reaction on 3DOM Ce-W-Nb x catalysts followed both Eley-Rideal and Langmuir-Hinshelwood mechanisms. The doping of Nb was beneficial to boost the adsorption of NH 3 and improved the reactivities of NH 3 adsorbed species while facilitating the generation of active NO x species. These accelerated the reaction rate and optimized the reaction path.