Calcium poisoning mechanism on the selective catalytic reduction of NO x by ammonia over the γ-Fe 2 O 3 (001) surface.

γ-Fe 2 O 3 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 γ-Fe 2 O 3 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 NH 3 -SCR over the γ-Fe 2 O 3 catalyst surface. The findings reveal that NH 3 , NO, and O 2 molecules can bind to the γ-Fe 2 O 3 (001) surface to generate coordinated ammonia, monodentate nitroso, and adsorption oxygen species, respectively. The main active site is Fe 1 -top. For the γ-Fe 2 O 3 with Ca poisoning, the Ca atom has a high adsorption energy on the surface of γ-Fe 2 O 3 (001), which covers the catalyst surface and reduces the active sites. The presence of Ca atom decreases the adsorption performance of NH 3 , while slightly improving the NO and O 2 adsorption. In particular, the Ca atom restrains the NH 3 activation and NH 2 formation, which is detrimental to the NH 3 -SCR process.