| Mercury pollution in the atmospheric environment is a matter of international concern.Mercury in coal-fired flue gas is the first human mercury emission source and has become the focus of national mercury pollution control.When coal is burned,its mercury will become part of the flue gas due to heat,mainly in the form of elemental mercury(Hg0),divalent mercury(Hg2+),and particulate mercury(Hgp),with elemental mercury accounting for Larger and not easily trapped by existing equipment,which is the main component of mercury that is emitted into the air.Therefore,how to convert the elemental mercury(Hg0)in the flue gas into easily-removed divalent mercury(Hg2+)is the main idea of mercury emissions control.Because of its high mercury removal efficiency and lower cost,the catalytic oxidation of elemental mercury is currently a research hotspot.Manganese oxides have strong catalytic performance and cerium oxides have strong oxygen storage capacity.in this study,the coprecipitation method was used,and the manganese and cerium composite oxides were supported on ?-Al2O3 with high specific surface area,and their mercury removal performance was investigated under different flue gas conditions and in a range of low temperature(50-250°C).The effect of Mn/Al molar ratio,Ce/Al molar ratio,preparation roasting temperature,reaction temperature and various components of flue gas(O2,NO,SO2,H2O,NH3)on zero-valent mercury removal efficiency was studied in detail,and the Mn-Ce/y-Al2O3 catalysts before and after the reaction were characterized by BET,SEM,XRD and XPS to analyze the physicochemical properties of the samples.Based on the experimental and characterization results,the mercury removal mechanism of the catalyst was analyzed.In view of the problem of catalytic reduction of the catalyst in the presence of SO2,metal Cu doping was used for optimization,and the experimental verification was performed under the same conditions.The principle of the improvement of the sulfur resistance of the catalyst was discussed in conjunction with the XPS analysis results.The experimental results show that after ?-Al2O3 is loaded with metal Mn and Ce,the mercury removal efficiency is greatly improved,and Mn and Ce have a good ability to synergistic mercury removal at low temperature.When the Mn/Al molar ratio is 0.1,the Ce/Al molar ratio is 0.02 and the reaction temperature was 150°C,the zero-valent mercury removal efficiency was the highest at 92%,and the zero-valent mercury removal rate was above 80%in the temperature window of 100 to 200°C.The experimental study on the effect of flue gas components(O2,NO,SO2,H2O,and NH3)on the mercury removal performance of Mn-Ce/y-Al2O3 catalysts shows that O2 in flue gas can greatly promote the oxidation of elemental mercury,and O2 concentration in coal-fired flue gas has been able to meet the demand for oxidation of elemental mercury;NO promotes the oxidation of zero-valent mercury,but is milder than O2;H2O and NH3 inhibit the oxidation of zero-valent mercury;SO2 strongly inhibits elemental mercury removal.Combined with the characterization results,the dispersibility of the active metal on Mn-Ce/y-Al2O3 is high.After loading metal,there are some tiny particles on the surface of the catalyst,and the particles are floccular,which has a certain role in promoting the adsorption capacity of the catalyst.In the presence of SO2,the addition of Cu helps to retain more highly valence active metals.Under the chlorine-free conditions,the mercury removal process of Mn-Ce/y-Al2O3 can be explained by the Mars-Maessen mechanism. |
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