| Nitrogen oxides (NOx) are one of the most notorious gaseous pollutants that cause the formation of ozone depletion, photochemical smog and acid rain, which endanger human health directly or indirectly. Selective catalytic reduction (SCR) of NOx to N2 is one of the most effective methods for denitrification of flue gas, among which catalyst is the key element of the DeNOx system. The research achievements for catalysts of SCR denitrifucation have been expanded, including reaction mechanism, the adsorption of reactant molecules on catalyst, and the main factors in deactivation of catalyst.To meet the coming severe emissions standards, it is necessary to develop SCR catalysts with high activity in a wide range of temperature. The cordierite honeycomb ceramics (CC) was coated with Mn, Cu, Ce modified TiO2 (or Mesopore Molecular Sieve MCM-41), V2O5 and WO3. A series of monolith catalysts were evaluated for the selective catalytic reduction (SCR) of NO by urea (32.5wt%). The physical and chemical properties of the catalysts were determined using nitrogen adsorption, CO2-TPD, NH3-TPD, XRD, XPS and H2-TPR experiments. This study provides a potential catalyst system for the removal of NOX from diesel engines.Mn, Ce modified TiO2 sol (noted as M) and Cu, Ce modified TiO2 sol (noted as C) were prepared by sol-gel method, and the cordierite honeycomb ceramics (CC) was coated with M or C, and V2O5-WO3 (noted as V) in sequence by impregnation method. The catalysts loaded using the sequential way showed higher BET surface areas than that using the alternative way, Which agrees with the catalytic activity. The improvement of M phase is much more pronounced than in the case of C phase at low temperatures and in reverse at higher temperatures. Both M and C phase are introduced, the catalyst V/3C/3M/CC exhibited the optimal NO removal efficiency over 80% at 200-550℃. The results of XRD suggested that the catalysts loaded using the sequential way showed the diffraction peak of anatase or rutile TiO2, while the catalysts loaded using the alternative way showed anatase TiO2 and WO3 peaks. The experiments of NH3/CO2-TPD indicated that the surface acidity and basicity were equivalent between the two series catalysts. The reduction behavior of the catalysts loaded using the sequential way and the alternative way were different, and showed good redox properties at a wide temperature range. Moreover, the catalyst prepared by alternative way showed a reduction at higher temperature, corresponding to the reduction of TiO2 and WO3. The XPS analysis results of all catalysts showed that Ti is in the form of TiO2, O existed in the two kinds of form, and the catalysts with higher V4+/V5+ ratio should have very higher activity.NO conversion of the monolith catalysts prepared by coating methods supported on nanometer titanium dioxide (TiO2) was rather larger than that on Molecular Sieve MCM-41. While the BET surface areas of MCM-41 were clearly higher than TiO2. The SCR performance of the monolith catalysts prepared by coating methods were significantly improved by adding Mn, Cu and Ce. The V-W-Cu-Mn-Ce-Ti-O/CC catalyst showed the best DeNOx activity between a wider temperature window, NO conversion on the complex catalyst maintained over 85% at the temperature range of 200-550℃. The active components in the surface of two kinds of catalysts is existed in the form of grain. Some cracks occurred on the surface of V-W-Cu-Mn-Ce-Ti-O/CC and V-W-Cu-Ce-MCM-41/CC. The XRD of TiO2 catalysts showed anatase TiO2 and WO3 peaks, while MCM-41 catalysts only showed the peak of CC. The introduce of Cu,Mn,Ce increased the acidity and basicity of catalysts surface, and the TiO2 catalysts showed much more stronger acidic site and basic sites. The reduction behavior of TiO2 catalysts were much better than MCM-41 catalysts. The more V4+ existed in the catalyst surface, the higher NO conversion was obtained. |
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