The promotion effect of niobium on the low-temperature activity of Al-rich Cu-SSZ-13 for selective catalytic reduction of NOx with NH3

Abstract

The effect of niobium (Nb) addition on the low-temperature activity and kinetics of Cu2%-SSZ-13 catalyst was evaluated by the selective catalytic reduction of NOx by ammonia (NH3-SCR) reaction. The low-temperature activity of Cu2%-SSZ-13 was dramatically enhanced by introducing a certain amount of Nb into Cu2%-SSZ-13 with excellent N2 selectivity and sulfur resistance obtained. The NOx conversion of Nb0.7%/Cu2%-SSZ-13 increased by 22.7% on average at 200–275 °C Even 67% NOx conversion can be obtained at 150 °C, much higher than that of Cu2%-SSZ-13. Characterization methods indicated that niobium ions entered into the cation exchange sites to increase the number of [Cu(OH)]+-Z which is the active site in low-temperature SCR. Furthermore, the formation of Nb = O enhanced the amount of the Lewis acid sites and the Brønsted acid sites on catalyst surface, promoting the NH3 adsorption capacity. The in situ DRIFTS results demonstrated that Nb0.7%/Cu2%-SSZ-13 could adsorb more NOx species, which reacted with NH4+ adsorbed on the Brønsted acid sites through the Langmuir-Hinshelwood (L-H) route, and that the coordinated NH3 on Lewis acid sites species played main roles as the main active intermediates in low temperature. It is revealed that Al-rich Nb0.7%/Cu2%-SSZ-13 zeolite catalyst has a competitive potential to be an NH3– SCR catalyst for NOx elimination in practical applications.