Reserches On Catalytic Decomposition Of H₂O₂/O₃ And Oxidation Of Flue Gas Denitration

Haze pollution is increasingly serious,which is resulted from the emmissions of nitrogen oixdes?NOx?.The flue gas temperatures of industrial furnaces,sincering machine and catalytic cracking unit are too low to be used in the selective catalytic reduction?320-400 0C?.To realize the low-cost flue gas denitrification,the easiest way is to oxidize NO to high soluble NO2 and be adsorbed with alkali solutions.In the present study,the catalytic decomposition of H2O2 and catalytic ozonation for denitrification ranging from 40 to 180 ?was proposed.The oxidation denitrification method can not only be used in the low-temperature flue gas,but also be used for ultra clean emissions after conventional desulfurization process in thermal power plant boiler.First of all,catalytic decomposition of H2O2 for denitrification was developed.The H2O2 was decomposed to ·OH and highly oxidizing substances over ?-Fe2O₃,which could remove NOx.The effects of flue gas temperature,preheating temperature,H2O2 flow rate and total flow/bypass flow on the denitrification were investigated.The results showed that when the flue gas temperature was 160 ?,the flow rate of H2O2 was 0.4 mL·min-1,the preheating temperature was 130 ?,the total flow/bypass flow was 6 and the NOx concentration was 550 x 10'6,the denitrification efficiency reached 78.0%.When the SO2 existed in the simulated flue gas,the SO2 removal remained above 99%even though the factors varied.On the basis of the above denitrification process,iron-aluminum composites?NIAO?x/y??were developed and the formation mechanisms were studied.The results showed that when the ratio of Fe/Al was 7/3?NIAO?7/3??,the NOx removal was the highest,which was up to 81.2%.Suitable content of aluminium NIAO?7/3?not only improved the surface areas and pore distributions of catalysts,but also resulted in a slight increase in the numbers of zero charge,the content increase of FeOH and oxidation ability of Fe???,promoting the the generation of ·OH and active substances,improving the NOx removal.However,excessive content aluminium?NIAO?3/7??led to the formation of spherical particles with aluminum surface enrichment,resulting in the formation of Fe-O-Al,reducing the number of active sites of FeOH,decreasing the ·OH and active substances,thereby decreasing the NOx removal.Secondly,the catalytic ozonation for denitrification was developed.The O₃ and H2O were conversed to ·OH and active substances over CeTi,which oxidized NOx to achieve the purpose of denitrification.When the O₃ concentration was 8.5 mg·L-1,the flue gas temperature was 40 ?,H2O flow rate was 2.4 mL·min-1,the total gas flow rate was 400 m·min-1,the denitrification efficiency was 95%.When the SO2 existed,the SO2 removal reached 99%in the same conditions with abosorption.Compared with the conventional flue gas treatment method,this one had no secondary pollution,less waste generation and low operating costs.The main byproducts,ammonium sulfate and ammonium nitrate,were the major fertilizers and industrial raw materials.The catalytic mechanisms of CeTi catalyst were deeply analyzed.Amorphous CeTi catalyst?Am-CeTi?and crystalline CeTi catalyst?Ct-CeTi?were prepared by co-precipitation method and impregnation method,and their catalytic ozonation catalyst was used as catalyst to remove NOx at the low temperature.The experimental results showed that the Am-CeTi catalyst had lower surface defects and surface-OH than Ct-CeTi,however,it has a higher Ce-O-Ti bond content and catalytic activity.Ce-O-Ti bond was confirmed to be the active site for catalytic ozonation of NOx.Fluorine?F?doped CeTi catalyst?CeTiF?was prepared and used for the NOx removal.CeTiF presented higher catalytic activity than CeTi.F doping reduced the surface-OH binding energies,improving the surface hydroxyl reaction activity,and promoting the production of ·OH.F-replaced the O2-in Ce-O-Ti and generated oxygen vacancies,which contributed to the adsorption of H2O,thus improving the catalytic activities.Finally,the selective denitrification process was achieved by injecting O₃ and ethanol mixtures into the simulated flue gas duct.The organic radicals,generated by the ethanol oxidation by O₃,could oxidize NO and NO2 to nitrate organics or aqueous nitrate acids,which were important industrial raw.The residual ethanol in the exhausted liquid phase could be recycling utilized.The experimental results showed that the CO₃2-,HCO₃-and SO2 in the flue gas hardly exhibit any effect on the NOx removal.Compared with the conventional O₃ oxidation removal process,the present method had higher selective oxidation of NO,higher NOx removal,lower SO2 oxidation and less O₃ demands.Besides,it has lower initial investment and operating costs with more compact equipment.More than 80%NOx removal is obtained under the following optimal experimental conditions.