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

NO, N2O and NO2 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 NO2 in the adsorbed state had a distinct change than that of N2O compared to their free gas state. [M′]-MAPO-5 was more effective for the activation of NOx 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 NOx followed the decreasing order of NO2 > NO > N2O. And adsorption complexes in η1-N mode were much stabler than that in η1-O mode, which was similar to that in [M′]-AlMOR. [Cu]-MAPO-5 had a much stronger adsorption for NOx than [Ag]-MAPO-5. And [M′]-SiMOR had a little stronger adsorption for NOx than [M′]-TiMOR. Furthermore, the resistance capabilities of [M′]-MAPO-5 to SO2, H2O and O2 were studied and analyzed. The interaction mechanism of NOx adsorption in [M′]-MAPO-5 was also discussed by natural bond orbital (NBO) analysis, which was in reasonable agreement with the adsorption interaction strengths.