Study On The Preparation Of Iron-based And Manganese-based Spinels And Their Catalytic Ozonation For Flue Gas NOx Removal

In recent years,China's air pollution situation further deteriorated,nitrogen oxides?NOx?emissions is one of the reasons for its formation.For industrial furnace,sintering machine,or catalytic cracking unit,the exhaust gas temperature is not suitable for the selective catalytic reduction of NOx by NH3?NH3-SCR?.As a kind of advanced oxidation technology,catalytic ozonation has been paid more and more attention by researchers.Studies have shown that the oxidation mechanism of catalytic ozonation of NOx does occur via hydroxyl radicals and hydroxyl radicals?·OH?has been confirmed to determine the catalytic performance of NOx removal.In order to study the promote effects of oxygen vacancies for catalytic ozonation reaction and further improve low-temperature catalytic activity,spinel and CO reduced spinel catalysts were prepared by hydrothermal method.The catalytic activities and catalytic mechanism were studied in the experiment.The performance of catalysts was investigated in a catalytic fixed-bed reactor.The results showed that the activity of CuFe₂O₄ catalyst was significantly improved compared with the previous two catalysts.Combined with a series of methods of analysis and testing,some important conclusions were summed up.From the XPS result,we drew the conclusion that the spinel catalyst variable valence makes oxygen vacancies easy to be introduced into the crystal lattice.The thermal weight?TG?and other data showed that spinel has more surface hydroxyl groups.It is proved that the synergetic effect of surface hydroxyl groups and oxygen vacancies plays an important role in the generation of hydroxyl radicals and thus enhancement of catalytic activity.The activity of CuFe₂O₄ was decreased after the long time stability test,which is disadvantageous for the practical applications.The catalysts should be further developed and studied.Based on theoretical foundation of catalysts CuFe₂O₄,and in order to improving low-temperature activity of spinel catalysts and further study the promotion mechanism of oxygen vacancies,catalysts CoMn₂O₄ and CO reduced CoMn₂O₄ were prepared by hydrothermal method in this study.The studies found that the CO reduced CoMnO4 showed better catalytic activity than that of CoMn₂O₄,and it showed more than 85%denitration efficiency.Combined with some characterization methods,we found that the oxygen vacancies in catalyst CoMn₂O₄.CO pretreatment makes the oxygen vacancy of CoMn₂O₄ catalyst increased.Due to the influence of reduced atmosphere,Co,Mn valence change promoted the generation of chemical adsorption oxygen and induce the generation of oxygen vacancies,thus enhanced the catalytic performance of the catalyst.The characterization of the fresh and used catalyst was performed and it showed that the catalyst stayed stable after the reaction due to the catalyst set on the by-pass.The catalyst shows great potential for industrial applications.