Catalyst Investigation Of Low-temperature Selective Catalytic Reduction Of Nitrogen Oxides With NH₃

Nitrogen oxides are the main air pollutants and also the important factor in the formation of photochemical smog. Controlling and remediation of the nitrogen oxides pollution are taken more attention at home and abroad in the field of environmental protection. The selective catalytic reduction (SCR) technology is an effective method for NOx reduction of flue gas of the stationary sources. The low temperature SCR denitration catalyst device can be directly loaded after the ESP, and it can be directly matched with the existing boiler systems, in which the economizer, the air preheater and the boiler are a whole assembly. Compared with high temperature SCR catalyst, that can not only avoid the energy consumption for preheating the flue gas, but also reduce smoke poisoning effect on the catalyst, and extend the catalyst life. It has important significance to research the SCR denitration catalyst for the low temperature reaction.Firstly, the denitration catalysts are prepared by volume impregnation method, in which A oxide is used as the main active component, B, C and other metal oxides are used as additives. By the characterization with scanning electronic microscopy, the A, B and C three metal oxides are determined as the active components of the catalyst, and the optimum calcination temperature of the catalyst is determined as 500℃. Based on that research, in this paper the Al2O3, TiO2 and ZSM-5 are used as the carriers to prepare low temperature SCR catalysts by the impregnation method, and the characterization is carried out with SEM, TPD and TPR. As to the research results, it is found that the A-B-C/Al2O3 catalyst has higher comprehensive performance overall, and when the Al2O3 is taken as carrier, the catalyst cost is the lowest, so the A-B-C/Al2O3 catalyst is choosed as the main research subject.Secondly, the test investigations of low temperature SCR denitration using the A-B-C/Al2O3 catalyst under different reaction temperatures are carried out, and it is found that this catalyst has higher denitration activity between 90℃ to 150℃, and the 120℃ is determined to be the optimal denitration temperature.Thirdly, the activated carbon is prepared by chemical activation method, then the denitration catalysts are prepared with the activated carbon, the Al2O3, and the composite of carbon and Al2O3 respectively. The denitration researches show that the denitration effect of A-B-C/Al2O3-AC catalyst is better than the other two catalysts’.Finally, the A-B-C/Al2O3, the A-B-C/Al2O3-AC, and the A-B-C/AC catalysts are selected to investigate SCR denitration with SO2 existing in flue gas, it can find that when the Al2O3-AC is taken as the composite carrier, the denitration efficiency can be improved. The conclusion showes that the activated carbon is conducive to denitration reaction, and that catalyst can remain high denitration activity with SO2 existing in the flue gas, thus improve the sulfur tolerance of the catalyst.