Preparation and performance of V-W/x(Mn-Ce-Ti)/y(Cu-Ce-Ti)/cordierite catalyst by impregnation method in sequence for SCR reaction with urea

Mn-Ce/TiO₂ (M) and Cu-Ce/TiO₂ (C) were prepared by sol-gel method, and the cordierite honeycomb ceramics (CC) was coated with M and/or C and V₂O₅-WO₃ in sequence by impregnation method. A series of monolith catalysts were evaluated for the selective catalytic reduction (SCR) of NO_x by urea. The physical and chemical properties of the catalysts were well examined using nitrogen adsorption, CO₂-TPD, NH₃-TPD, XRD, XPS and H₂-TPR experiments. The results showed that when the M phase was coated onto catalyst prior to C phase, the complex catalyst V/3C/3M/CC was more active than the catalysts with only M or C phase in the presence of 0.01% SO₂ and 10% H₂O, and a small quantity of SO₂ may favor the urea-SCR activity. XRD analysis indicated that Cu, Ce modified TiO₂ sol favors the formation of anatase phase, and Mn, Ce modified TiO₂ sol facilitates the formation of rutile phase. The BET surface area of catalyst only has relationship with the amount of M or C phase, and loading sequence does not influence it so much. The introduction of M phase and C phase increases the surface acid sites of different intensity. H₂-TPR results showed the interaction between vanadium and copper and/or manganese species enhances the reduction of vanadium, which can increase the amount of H₂ consumption. XPS results indicated that both high V⁴⁺/V⁵⁺ ratio and large amount of surface chemisorbed oxygen may beneficial to the activity of the catalysts.