| Currently ammonia-selective catalytic reduction (NH3-SCR) is considered one of the most effective technologies for NOx removal in the flue gas technology. The commercialized industrial catalysts for NH3-SCR of NO mainly are V2O5-WO3/TiO2, which shows high activity and well tolerant to the SO2. But the catalysts must operate at a reaction temperature between330～400℃. In order to avoid the deactivation by SO2and dust, SCR reactor should be located downstream of the particle control and the desulfurizer devices where the flue gas temperature is usually below150℃. Therefore, it is needed to develop superior SCR catalysts at low temperatures.As the low-termperatures SCR catalyst studied mostly were the powder or granules catalyst, which were limited due to the drop of bed pressure as industrial applications. Since cordierite honeycomb ceramic with high strength, low pressure drop and good heat stability, it widely used in catalytic conversion, other chemical and environmental fields.In view of the above problems and analysis, the TiO2was prepared by sol-gel method. Cordierite monolithic catalysts was prepared firstly by sol-gel method for TiO2/cordierite, then by impregnation method for Mn-Ce/TiO2/cordierite monolithic catalyst and used for low-temperatures SCR of NOx with ammonia. The purpose is to find a catalyst which is high activity at low temperatures and wide temperatures window in NOx removal catalyst. Main conclusions of this dissertation are as follows:(1) The SCR activity on Mn-Ce/TiO2/CC catalyst is significantly better than that on the Mn/TiO2/CC catalyst. The Mn-Ce(0.15)/TiO2/CC catalyst, calcinated at400℃and Ce/Mn=0.15(molar ratio), exhibits excellent denitration activity at low temperatures. The NOx conversion exceed70%at80℃and remained above96%in the range of120～200℃.(2) The reaction conditions, such as NO inlet concentration, space velocity ratio (GHSV), O2concentrations and ammonia nitrogen ratio (NH3/NO) affect the activity of denitrification. But the catalyst still showed a superior activity on a high NO inlet concentration, high space velocity and hypoxic conditions.(3) Transient response experiment showed on Mn-Ce/TiO2/CC catalyst, NH3is not in gaseous form to react, but the adsorbed NH3react with NO. The NO in the form of gaseous or weakly adsorbed react with the adsorbed NH3. Oxygen played an important role in SCR process and promoted the generation of surface chemisorption oxygen, the supplement of lattice oxygen and the adsorption of NO. The original weakly adsorbed NO would be desorbed when oxygen will be removed.(4) The BET analysis and NH3adsorption experiments indicated the surface area, total pore volume and micropore volume of the Mn/TiO2/CC catalyst modified by Ce which enhanced the adsorption and activation of the NH3increased slightly.(5) The XPS analysis and NO oxidation activity experiment showed that the Mn/TiO2/CC catalyst modified by Ce improved the content of MnO2on catalyst surface, and increased the surface lattice oxygen and chemisorption oxygen. As the amount of the chemisorption oxygen on the Mn-Ce/TiO2/CC is more than Mn/TiO2/CC, which improve the oxidation activity of NO to NO2.(6) H2-TPR test showed that the catalyst after doping Ce moved the reduction peak to lower temperature. The result indicated there may be some synergy between Mn and Ce which can move the reduction peak temperature of the surface species to the lower temperature. So the redox capacity of the catalyst would be greatly improved, thus contributing to the catalytic reaction. |
PDF Full Text Request