The Study And Application Of Hybrid Combination Technology Between Fe-Mn/ZSM-5 And Fe-ZSM-5 For SCR Of NO_x With NH₃

The SCR denitration catalysts with higher activity,selectivity,and thermal stability over a wide temperature range,could be prepared using methods rather than the chemical modification.The hybird catalyst,mechanically assembled by mixed metal oxides and molecular sieve catalyst,contributed to the catalytic reaction utilizing the cooperation of two reaction systems.The combination process of the existing catalysts should be therefore studied,and by deploying the cooperation of two reaction systems,the catalytic performance from low temperature to high temperature could be improved.In present thesis,Fe-ZSM-5?CVD?with good thermal stability and Fe-Mn/ZSM-5?CPP?with high low-temperature activity were selected to analyse the assembly process.The combination of CVD and CPP was carried out by grinding mixture?GCC?,particle mixing?MCC?,CPP placed upstream of CVD?UCP-DCV?and CVD placed upstream of CPP?UCV-DCP?,among which sample UCV-DCP possessed optimal denitration activity.Adjusting the mass ratio of CVD and CPP,with keeping the total mass of UCV-DCP,the optimum ratio was 1:9.SEM,XRD,NO oxidation experiments,NO+O₂-TPD,NH₃-TPD,H₂-TPR,and XPS were selected to analyse the influences of combination patterns and ratios in activity.Some powder catalysts were coated on cordierite to prepare monolithic catalysts,and the physical assembly process of monolithic catalysts was also investigated.The following conclusions were achieved mainly:?1?Among the four mentioned samples,UCV-DCP was the optimum combination mode.After the physical combination,the basic chemical properties of CVD and CPP were unchanged,and existed little difference in acidity of combined samples,with abundant adsorbed NH₃.So all these aspects were not the main factors affecting SCR activity.?2?The key factor affecting the catalytic activity was the combined structure of CVD and CPP.UCV-DCP with unique mode denoted as effective coupling structure,generated more NO₂ and inhibited the excessive oxidation of NH₃.It therefore maintained higher catalytic activity at low temperature,and simultaneously owned better mid-high temperature activity.Due to its high NO oxidation capacity and effective combination mode,UCP-DCV generated more NO_x-intermediates and higher low-temperature activity,but its activity at high temperature was severely inhibited by the overoxidation of NH₃.?3?Sample UCV-DCP?1:9?with the mass ratio of CVD to CPP being 1:9,had excellent high-temperature activity and meanwhile facilitated its low-temperature activity.The mass ratio affected the yield and types of NO_x-intermediates.Only on sample UCV-DCP?1:9?,a synergistic interaction between CVD and CPP occured,which promoted the formation of reactive intermediates while limited the inhibiting species,then the best low-temperature catalytic activity was achieved.?4?The low-temperature reaction followed the L-H mechanism,and its activity was controlled by yield and types of NO_x-intermediates.Nitrites and monodentate nitrate promoted activity,while monometallic bidentate nitrate inhibited low-temperature reaction rate.Bimetallic bidentate nitrates and"Fast-SCR"acted synergistically in activity at mid-high temperature.At high temperature,the reaction between gas phase NO and-NH₂ occured,following the E-R mechanism.?5?The combined monolithic catalyst UCV-DCP/CC integrated the advantages of both catalysts,which simultineously possessed high activity at low and high temperature.Its activity rule was consistent with the particle catalyst,indicating that the key factor influencing the reactivity was not cordierite carrier and its structure properties,but the factors affecting the activity of the granular combination sample.