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

Fe3O4, alpha-Fe2O3 and gamma-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 alpha-Fe2O3, gamma-Fe2O3 and Fe3O4 catalysts, supporting the DFT calculations. The adsorption energy of ammonia and nitric oxide on alpha-Fe2O3 (001), gamma-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 (1 1 1) 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.