Investigation on NOx adsorption in [M′]-MAPO-5 (M = Si, Ti; M′ = Ag, Cu) by density functional theory calculation

Abstract NO, N 2 O and NO 2 adsorption in [M′]-MAPO-5 (M = Si, Ti; M′ = Ag, Cu) models of the modified aluminophosphate molecular sieves was investigated by density functional theory (DFT) method. The equilibrium structural parameters and adsorption energies were obtained and compared. The structural parameters of NO and NO 2 in the adsorbed state had a distinct change than that of N 2 O compared to their free gas state. [M′]-MAPO-5 was more effective for the activation of NO x molecule compared to [M′]-AlMOR (M′ = Ag, Cu) models of the modified mordenite in our previous studies. The adsorption energies data indicated that adsorption strength of NO x followed the decreasing order of NO 2  > NO > N 2 O. And adsorption complexes in η 1 -N mode were much stabler than that in η 1 -O mode, which was similar to that in [M′]-AlMOR. [Cu]-MAPO-5 had a much stronger adsorption for NO x than [Ag]-MAPO-5. And [M′]-SiMOR had a little stronger adsorption for NO x than [M′]-TiMOR. Furthermore, the resistance capabilities of [M′]-MAPO-5 to SO 2 , H 2 O and O 2 were studied and analyzed. The interaction mechanism of NO x adsorption in [M′]-MAPO-5 was also discussed by natural bond orbital (NBO) analysis, which was in reasonable agreement with the adsorption interaction strengths.