Ce doping to Cu-SAPO-18: Enhanced catalytic performance for the NH3-SCR of NO in simulated diesel exhaust

The Ce-Cu-SAPO-18 catalysts were prepared by the ion exchange method. The Ce-Cu-SAPO-18-2 catalyst with a Ce content of 1.24 wt% showed the excellent NH3-SCR activity. Characterization results demonstrated that the Ce-Cu-SAPO-18-2 catalyst possessed strong redox ability and high reactive nitrate and NH3 species, which were responsible for the remarkable SCR performance. The best-performing Ce-Cu-SAPO-18-2 catalyst displayed a broad operation temperature window, a result possibly due to the improvement of physicochemical properties and acceleration of reaction rate in the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. The higher amounts of isolated Cu2+ species and acid sites in Ce-Cu-SAPO-18.2 promoted the adsorption and activation of NO, and facilitated the reaction between the adsorbed NOx species and the gas-phase NH3 molecules according to the L-H mechanism. For the E-R mechanism, the NH3 (L) species were the crucial initial intermediates for NH3 activation, and the more amount of Lewis acid sites in the Ce-Cu-SAPO-18-2 sample originated from its coordinatively unsaturated cationic sites benefited the reaction between the adsorbed NH3 species and NO molecules. Based on the results of in situ DRIFTS characterization, we believe that the L-H mechanism dominated the NH3-SCR reaction at low temperatures, and the doping of Ce in the catalyst improved the L-H and E-R reactions at low temperatures.