Low-Temperature SCR DeNO_x Performance Of Foam Metal Nickel-Supported Mn-Based Catalysts

Nitrogen oxides are a common atmospheric pollutant.Coal-fired thermal power plants are one of the major nitrogen oxide emission sources in China.It is extremely urgent to control and reduce their nitrogen oxide emissions.There are so many advantages of economy,high efficiency for the NH₃-SCR de-NO_x process,and it has become the mainstream process for de-NO_x from the boiler flue gas of thermal power plants.At present,coal-fired thermal power plants and other fixed sources widely use V₂O₅-WO₃/TiO₂ catalysts to de-NO_xemitted from them.V₂O₅-WO₃/TiO₂ catalysts have good de-NO_x efficiency and anti-SO₂ poisoning performance in the mid-temperature section,but their de-NO_x activity temperatures are too high,the price is expensive,vanadium is easy to lose,they easily lead to secondary pollution,and other shortcomings.Therefore,it is particularly urgent to develop a highly efficient,low-pollution,low-cost de-NO_x catalyst suitable for China's national conditions.In order to avoid repeated heating of the flue gas,the SCR reactor with conventional commercial catalysts must be installed before the desulphurization and dedusting device,and the high concentration of dust in the flue gas phase will affect the de-NO_x performance of the catalyst and reduce the service life of the catalyst.The low-temperature de-NO_x process allows the SCR reactor to be placed behind the electrostatic precipitator,reducing the impact of dust erosion on the catalyst,making this process of concern.The development of low-temperature de-NO_x catalysts is the core of this process.In this dissertation,a series of Mn_x/FMN low-temperature de-NO_x catalysts were prepared by impregnation method.Firstly,the effects of preparation process and experimental conditions on the low-temperature de-NO_x efficiency of Mn_x/FMN catalysts were studied.Secondly,the anti-alkali metal K performance of Mn_7.5/FMN catalyst was also studied.Based on this,the modification of Mn_7.5/FMN catalyst was optimized and the reaction kinetics of each catalyst was preliminary discussed,the surface properties and activation energy of the catalyst were analyzed.The main results are as follows:?1?The calcination temperature in the catalyst preparation process has a great influence on the low-temperature de-NO_x performance.The unsaturated Ni atoms,structural defects,and number of surface acid sites on the surface of the Mn_7.5/FMN catalyst calcined at 350? were greater than those of the Mn_7.5/FMN catalyst calcined at 550?.Therefore,the Mn_7.5/FMN catalyst calcined at 350? exhibits excellent low-temperature de-NO_x performance,and it is close to 100%within the test temperature range of 120-200?.It was found that when the calcination temperature exceeds 350?,the activity of the catalyst is decreased due to the better crystallinity of Mn₂O₃ and Ni O.The study on the mechanism of low temperature denitration of Mn_7.5/FMN catalysts shows that the reaction mechanism of Eley-Rideal?E-R?and Langmuir-Hinshelwood?L-H?coexist,but the E-R mechanism plays a major role.?2?The performance of a Co-modified Ni-foam supported Mn-based SCR deNO_x catalyst with respect to alkali–metal poisoning resistance in flue gas at 120-240? was investigated.With increasing K content,the alkali resistance and deNO_x activity of the Mn/Ni-foam?Fresh?catalyst decreased.When the K load reached 0.3%,the activity of the catalyst was reduced to less than 30%.For the K_0.3Co_0.5/Fresh catalyst,the Mn⁴⁺/Mn_total,sat I/main peak,sat II/main peak and O_?/O_totalotal ratios increased,but the Mn³⁺/Mn_totalotal ratio decreased slightly.K destroys the Br?nsted acid sites that play an important role in adsorbing and activating NH₃,which is responsible for the decreased reduction performance of K_0.3/Fresh.Additionally,NH₃-TPD and in situ DRIFT analyses showed that the number of Br?nsted acid sites and Lewis acid sites on the K_0.3Co_0.5/Fresh catalyst surface were greatly increased.Therefore,the catalyst de-NO_x activity and K poisoning resistance were enhanced,especially at 120-160?,where the K_0.3Co_0.5/Fresh catalyst de-NO_x activity was higher than that of the Fresh catalyst.The added K or Co interacted with Mn and Ni on the catalyst surface and changed the redox performance of the catalyst.The amount of reducing sites on the K–poisoned catalyst surface decreased,and the redox performance also substantially decreased.After Co modification,the redox performance remained the same.However,the K resistance of the catalyst was dramatically improved.?3?The influence of internal and external diffusion on the deNO_x activity of catalyst was eliminated under the condition of large flow rate and a small amount of catalyst.Then basis on this,the activation energy of Fresh catalyst was studied,and the influence of K poisoning and Co modification on activation energy of catalyst was compared.The activation energies of Fresh and Co_0.5/Fresh catalysts were 17490.129J·mol^-11 and 15468.796 J·mol^-1,respectively.However,the activation energy of K_0.3/Fresh catalyst was increased to 35206.614 J·mol^-11 due to the K poisoning,but the activation energy of K_0.3Co_0.5/Fresh was decreased to 21980.886 J·mol^-11 after Co modification.Lower activation energy may be the reason why Fresh,Co_0.5/Fresh,and K_0.3Co_0.5/Fresh catalysts have better low temperature SCR activity.