Research On Modification And Performance Of MnCeTiO_x For Selective Catalytic Reduction Of No_x With NH₃ At Low Temperature

Nitrogen oxides（NO_x）are one of the main causes of air pollution problems such as acid rain,photochemical smog,ozone depletion,and smog,which seriously harm the ecological environment and human health.Atmospheric pollutants such as sulfur dioxide（SO₂）,NO_x and fine particulate matter in China are mainly derived from industrial source smoke and motor vehicle exhaust.Nitrogen oxide emission control is in line with the country’s major strategic needs of"fighting the battlefield of pollution prevention and control".At present,the industry’s mature and efficient NO_x removal technology is ammonia selective catalytic reduction（NH₃-SCR）technology,which has been successfully used for NO_x treatment of coal-fired flue gas and diesel exhaust.However,the exhaust gas temperature of China’s coke-making chemical industry and other industrial furnaces is low,and the composition is complex.Traditional SCR catalysts face problems such as low temperature catalytic activity,poor selectivity,and SO₂poisoning.The development of a low-temperature SCR catalyst resistant to SO₂poisoning is the key to the successful use of SCR technology in the removal of NO_x from flue gas in complex low-temperature industrial furnaces.In view of the above problems,this article takes Mn Ce Ti O_x catalyst as the research object,and studies its low-temperature SCR denitration performance,anti-SO₂and H₂O performance and reaction mechanism.The main results and conclusions are as follows:（1）During the preparation of the catalyst,the order of addition of the precipitant,the type of titanium source and the molar ratio of polyethylene glycol,manganese,cerium and titanium have significant effects on the structure of the catalyst,the low-temperature SCR denitration performance and the resistance to SO₂ and H₂O.Using titanium sulfate as the titanium source and polyethylene glycol as the template agent,the Mn Ce（0.5）Ti O_x catalyst prepared by co-precipitation（salt solution and precipitant added together）co-precipitation method has NO conversion higher than 90%at 160-360°C,with high N₂selectivity（N₂ selectivity is above 80%at 100-300°C）and good resistance to SO₂ and H₂O performance（NO conversion maintained at 52%at 260°C）.The increase of Ce addition can increase the specific surface area of the catalyst,enhance the redox performance and surface acidity of the catalyst,promote the adsorption of NH₃ on the catalyst surface,and improve the catalytic activity of the catalyst.（2）In order to improve the low temperature activity of the catalyst and the resistance to poisoning by SO₂ and H₂O,Sm was used to modify the Mn Ce Ti O_xcatalyst.The Mn Ce Sm（0.3）Ti O_x catalyst has a higher specific surface area,which is a structure composed of amorphous nanoparticles and nanocrystals,and has a stronger surface acidity and redox capacity than the Mn Ce Ti O_x catalyst,so that its denitration activity is higher.In the range of 140-320°C,the NO conversion of the catalyst can be close to 100%,and the selectivity of N₂ can reach 100%in the range of 100-320°C.After introducing H₂O and SO₂ into the reaction system,the catalyst can still maintain excellent catalytic performance（NO conversion maintained at 82%at 260°C）.（3）The SCR reaction mechanism of Mn Ce Sm Ti O_x catalyst was studied by in-situ DRIFTS methods,and the mechanism of Mn,Ce,Sm and Ti species in SCR reaction was studied.Combined with XPS results,it is found that NO is adsorbed and oxidized to active NO_x by surface O^*species from Ce O_x,which can then react with adsorbed NH₃^*mainly on the surface of Mn O_x following the Langmuir-Hinshelwood（L-H）mechanism at low temperature.Adding Sm facilities the formation of active NO_x（adsorbed NO₂ and bidentate nitrate）.The intermediates are easier to adsorb on the surface of the active site than SO₂,thereby improving the ability of the active site to resist poisoning by SO₂.