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

A string of 3DOM Ce-W-Nb ternary catalysts for NH3-SCR were prepared by a colloidal template method. The 3DOM Ce-W-Nb0.15 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 H2O and SO2. 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-Nbx catalyst, which was conducive to the good SCR performance at high temperatures. The NH3-SCR reaction on 3DOM Ce-W-Nbx catalysts followed both Eley-Rideal and Langmuir-Hinshelwood mechanisms. The doping of Nb was beneficial to boost the adsorption of NH3 and improved the reactivities of NH3 adsorbed species while facilitating the generation of active NOx species. These accelerated the reaction rate and optimized the reaction path.