Significant promoting effect of Ce or La on the hydrothermal stability of Cu-SAPO-34 catalyst for NH3-SCR reaction

The effect of Ce or La on the hydrothermal stability of Cu-SAPO-34 catalyst was evaluated by the selective catalytic reduction of NOx by ammonia (NH3-SCR) reaction after hydrothermal aging at 700 degrees C in 10 vol% H2O/air for 10 h. The hydrothermal stability of Cu-SAPO-34 was dramatically enhanced by introducing small amount Ce or La into Cu-SAPO-34. More than 93% NOx conversion was maintained over the aged Ce or La modified CuSAPO-34 at 175-350 degrees C, while extremely poor NH3-SCR activity was obtained over the aged Cu-SAPO-34. In situ diffuse reflection infrared Fourier transform spectrum (DRIFTS) results illustrated that the hydrothermal treatment cut off the intrinsic "E-R" reaction route over the Cu-SAPO-34 and opened the new reaction pathway ("L-H" mechanism) over the La modified Cu-SAPO-34 catalyst. Additionally, the introduction of Ce or La effectively mitigated the dealumination progress and restrained the aggregation of copper species over Cu-SAPO-34 during the hydrothermal aging, further maintaining the relatively large specific surface area and uniform pore size distribution. Meanwhile, the incorporation of Ce or La enhanced the redox property and stabilized the surface acid sites of Cu-SAPO-34, further facilitating the adsorption and activation of reactants.