Experimental Study On Removal Of NO And Hg~0 From Flue Gas By Microwave Catalytic Loaded Molecules Sieve

Composition of energy in China are rich coal,poor oil and little gas,coal will dominate energe consumption for a long time.Coal combustion will produce various gaseous pollutants,among which Hg⁰ and NO as the main pollutants have received critical attention in recent years.At present,the mature methods for denitrification and mercury removal of coal-fired flue gas are selective catalytic reduction and activated carbon injection adsorption,although these methods have high removal efficiency,they have the disadvantages of ammonia escape,complex system,large occuping area and high oper ation and maintenance costs.Therefore,developing highly efficient,economical and low secondary pollution new technology of denitrification and mercury removal has become a research hotspot in the field of air pollutant control.Microwave（MW）,a low-energy electromagnetic wave,has been successfully applied to the purification of gas pollutants owing to its advantages of fast heating rate,low activation energy and selective“hot spots”.In this paper,loaded molecular sieve catalysts were prepared by impregnation method,and the performance of Hg⁰ and NO removal was investigated under MW catalysis,the main work is as follows:A manganese oxide loaded molecular sieve catalyst with outstan ding MW absorption ability was synthesized and utilized for Hg⁰removal.By comparing the removal efficiencies under conventional thermal and MW catalysis,it’s found that MW not only improved the removal efficiency,enhanced the sulfur resistance,also broadened the effective temperature range（150～450℃）.Moreover,kinetic analysis revealed that MW improved the reaction rate and reduced the activation energy for Hg⁰ removal.A maximum Hg⁰ removal efficiency of 97.88%was achieved when 5 wt.%Mn@MOS and MW were used together with the GHSV of 45000 h^-1,temperature of 200℃andO₂concentration of 5%.Meanwhile,the stability of Mn@MOS was verified by the long-term operating experiment,and the destination of mercury was also revealed,most of Hg⁰ was chemisorbed by Mn@MOS,only a small amount was converted to gaseous Hg²⁺.Finally,the removal mechanism was speculated:the surface of Mn@MOS was excited to generate active sites,being conducive to the adsorption and oxidation of Hg⁰;both the adsorbed oxygen and lattice oxygen released by electron transfer between manganese oxides andO₂ in flue gas played crucial roles in the removal of Hg⁰.In order to further improve the catalytic activity of Mn@MOS,Fe-Mn@MOS was prepared by co-loading Fe and Mn onto MOS,and the performance of denitrification was investigated under MW irradiation.Results indicated that,MW is superior to conventional thermal catalysis in NO oxidation（90.5%vs 70.6%）;moreover,MW enables the catalyst to have excellent low-temperature activity（100～200℃）and good sulfur and water resistance.The IC analysis showed that the amount of NO₃^-and NO₂^-accounted for more than 90.0%of the N products,and the main product gradually changed from nitrate to nitrite as the reaction proceeded,owing to s shift in the main reaction pathway for NO removal.Mechanistic speculations indicate that NO oxidation is dominated by non-radical catalyzed reactions:（ⅰ）the reaction of chemisorbed NO on Mn（Ⅳ）withO₂^*(chemisorbed oxygenO_ads)to form nitrite;（ⅱ）the reaction of NO^*generated by MW excitation with reactive O^*（generated by the interaction of oxygen vacancies andO₂）to form nitrite.The research results of this thesis provide new ideas for the developme nt of novel denitrification and mercury removal materials and related technologies.