New insights into MnCeO_(x)/TiO_(2) composite oxide catalyst:Barium additive accelerated ammonia conversion

MnCeO_(x)/TiO_(2)has been widely used in selective catalytic reduction(SCR)of NO_(x)at low temperature.However,it is often poisoned in the presence of water vapor and sulfur dioxide.In this work,the promotion mechanism of Ba modification was investigated.Results show that the doped BaO reacts with CeO_(2)and forms BaCeO_(3).This unique perovskite structure of BaCeO_(3)significantly enhances NO oxidation and NH_(3)activation of MnCeO_(x)/TiO_(2)catalyst so that the NO conversion and the resistances to SO_(2)improve.It is found that Ba species obviously promotes the NO adsorption ability and improve the redox properties of MnCeO_(x)/TiO_(2)catalyst.While the acid properties of the catalyst are inhibited by Ba modification and among which Lewis acid sites are dominant for both MnCeO_(x)/TiO_(2)and MnCe(Ba)O_(x)/TiO_(2)catalysts.Furthermore,in situ DRIFT experiments reveal that the NO reduction upon MnCeO_(x)/TiO_(2)and MnCe(Ba)O_(x)/TiO_(2)catalysts follows both E-R and L-H mechanisms,in which L-H is preferred.Ba species enhances the formation of active nitrate species,which accelerates the NO reduction through L-H mechanism.It is interesting that although Ba species weakens the NH_(3)adsorption,it induces the ammonia conversion to coordination ammonia,which in turn accelerates the catalytic reaction.

Synergistic catalytic removals of NO,CO and HC over CeO_2 modified Mn-Mo-W-O_x/TiO_2-SiO_2 catalyst

A series of Mn-Mo-W-O_x/TiO_2-SiO_2 catalysts was modified with CeO_2 using an extrusion molding method. The catalytic activities of the obtained catalysts were tested for the synergistic catalytic removals of CO, NO and C_3H_8. The ratio of catalyst composition on catalytic activities for NH_3-SCR was optimized, which reveals that the molar ratio of Ti/Si was 9：1 and the catalyst containing 1.5 wt% CeO_2 and 12 wt% Mn-Mo-W-O_x exhibits the best catalytic performances. These samples were characterized by XRD, N_2-BET, Py-IR, NH_3-TPD, SEM/element mapping, H_2-TPR and XPS, respectively. Results show that the optimal catalyst exhibits more than 99% NO conversion, 86% CO conversion and 100% C_3H_8 conversion under GHSV of 5000 h^（-1）. In addition, the GHSV has little influence on removal of NO when it is less than 15,000 h^（-1）. Furthermore, the addition of CeO_2 will enhance the surface acidity, increase Mn^（4＋）concentration and inhibit the grain growth, which are favorable for the excellent catalytic performance.Anyway,the 1.5 wt% CeO_2-12 wt% Mn-Mo-W-O_x/TiO_2-SiO_2 possesses outstanding redox properties,abundant acid sites and high Mn^（4＋） concentration, which provide a guarantee for synergistic catalytic removal of CO, NO and HC.