Microscopic Mechanism of Fe₂O₃-Catalyzed NO Reduction during Sludge Combustion: A Density Functional Theory Study

Systematic studies on the mechanism underlying Fe2O3-catalyzed NO reduction in a reducing atmosphere during sludge combustion remain limited. In this study, density functional theory was employed to investigate the adsorption properties of NH3, CO, and NO on the alpha-Fe2O3(001) surface, and the mechanisms underlying the NH3 and CO reduction of NO during the adsorption process. The results demonstrated that NH3, CO, and NO chemically adsorbed on the surface Fe top site, thereby generating distinctly high adsorption energies. NO exhibited the highest adsorption energy. With regard to the catalytic mechanisms of NH3 and CO during NO reduction, the alpha-Fe2O3(001) surface exhibited different characteristics. NH3 reduction of NO tended to follow the Eley-Rideal (E-R) mechanism. The dissociation of -NH2NO is the rate-determining step for the NH3 reduction of NO. The presence of alpha-Fe2O3(001) reduced the dissociation energy barriers of NH3 and NH2NO, thereby catalyzing the reduction reaction. In contrast, NO dissociation was more challenging during the CO reduction of NO. The alpha-Fe2O3(001) surface reduced the dissociation barrier of the NO-NO dimer from 2.04 to 1.53 eV. Two adsorbed NO molecules first formed NO-NO dimers; these then dissociated into N2O and atomic oxygen, thereby catalyzing the reduction reaction.