Promotional effect of H2O2 modification on the cerium-tungsten-titanium mixed oxide catalyst for selective catalytic reduction of NO with NH3

摘要

Several cerium-tungsten-titanium mixed oxide catalysts were prepared through the hydrothermal precipitation method, and the influence of H2O2 modification on the NH3-SCR activity of Ce20W10Ti100Oz was investigated. The samples were characterized by XRD, N-2 adsorption-desorption, XPS and NH3-TPD to reveal the effect of H2O2 modification on its structure properties and redox properties. In addition, the NH3-SCR mechanisms at 200 degrees C for Ce20W10Ti100Oz catalyst modified by 2 ml H2O2 (1 mol/L) was also studied by in situ DRIFTS. The NH3-SCR activity of Ce20W10Ti100Oz was improved by H2O2 modification, and the suitable volume of H2O2 (1 mol/L) is 2 ml. The introduction of H2O2 refined the pore size of Ce20W10Ti100Oz and enlarged its BET surface area. In addition, H2O2 modification improved the molar ratio of Ce3+/Ce4+ on the surface of catalyst and made large amount of active oxygen belonging to surface hydroxyl formed on its surface with the total concentration of the active absorbed oxygen (O alpha + O'(alpha)) enhanced. They all contributed to enhance the NOx conversion over Ce20W10Ti100Oz catalyst. The intensity of acid sites for Ce20W10Ti100Oz was also improved by H2O2 modification, especially the Bronsted acid sites. Ionic NH4+ adsorbed on the Bronsted acid sites was mainly the active adsorbed NH3 species in the NH3-SCR reaction at 200 degrees C, and the reaction between active adsorbed NH3 species and gaseous NOx mainly occurred on Ce20W10Ti100Oz-2 at 200 degrees C following the E-R mechanism.