Calcium poisoning mechanism on the selective catalytic reduction of NOx by ammonia over the γ-Fe2O3 (001) surface

gamma-Fe2O3 has an excellent low-temperature selective catalytic reduction (SCR) deNO(x) performance, but its resistance to alkaline earth metal calcium (Ca) is poor. In particular, the detailed mechanism of Ca poisoning on the gamma-Fe2O3 catalyst at the atomic level is not clear. Hence, the density functional theory method was used in this research to investigate the influence mechanism of Ca poisoning on the NH3-SCR over the gamma-Fe2O3 catalyst surface. The findings reveal that NH3, NO, and O-2 molecules can bind to the gamma-Fe2O3 (001) surface to generate coordinated ammonia, monodentate nitroso, and adsorption oxygen species, respectively. The main active site is Fe-1-top. For the gamma-Fe2O3 with Ca poisoning, the Ca atom has a high adsorption energy on the surface of gamma-Fe2O3 (001), which covers the catalyst surface and reduces the active sites. The presence of Ca atom decreases the adsorption performance of NH3, while slightly improving the NO and O-2 adsorption. In particular, the Ca atom restrains the NH3 activation and NH2 formation, which is detrimental to the NH3-SCR process.