Insight into highly efficient FeOx catalysts for the selective catalytic reduction of NOx by NH3: Experimental and DFT study

Abstract

Fe3O4, α-Fe2O3 and γ-Fe2O3 catalysts were synthesized and showed excellent activities for the selective catalytic reduction (SCR) of NOx by NH3 in the temperature range that was between 433 K and 653 K in the presence of excess oxygen. Physical and chemical properties of catalysts were tested to investigate the effect of the iron oxides on the NH3-SCR activities by a series of characterization methods that were XRD, H2-TPR, NH3-TPD, BET and XPS. The related results indicated that the species of iron oxides had significant effects on oxidation–reduction ability, surface acidity distribution, BET surface area and surface adsorbed oxygen. Meanwhile, DRIFTS tests were carried out to further investigate the reduction process over α-Fe2O3, γ-Fe2O3 and Fe3O4 catalysts, supporting the DFT calculations. The adsorption energy of ammonia and nitric oxide on α-Fe2O3 (001), γ-Fe2O3 (001) and Fe3O4 (111) surfaces are calculated by the Density Functional Theory (DFT) calculations, suggesting that ammonia and nitric oxide are easily adsorbed on the Fe3O4 (111) surface. Moreover, it is reasonable to draw a conclusion that more surface chemisorbed oxygen, easier adsorption of reaction gases (NO, NH3 and O2) and more effortless oxidative dehydrogenation process can promote NH3-SCR.