Properties Of Carbon Nanotube-supported Iron-based Catalyst For Low-temperature DeNO_x

Selective catalytic reduction (SCR) denitration technology is currently the most widely used fixed source denitration technology, and the catalyst is the key of SCR technology. Currently, vanadium-based catalyst widely used in industry has many problems, which has not met the needs of modern industry. It is imminent to develop novel environmentally friendly low-temperature SCR denitration catalyst. Iron-based catalyst is considered to be a suitable replacement due to its advantages of being cheap, being green, stability, good resistance to sulfur and water. At present it has been widely studied. However, the poor low-temperature activity of iron-based catalyst has limited its further studies in low-temperature SCR. Some researchers considered to use appropriate carrier to improve the performance of iron-based catalysts. Carbon nanotubes (CNTs) become the focus of the catalyst carrier because of its unique structure and electronic properties, which has been applied to many reactions. The research found that CNTs benefit for the improvement of the low-temperature activity. In this paper, a very simple ethanol-assisted impregnation method was used to prepare Fe2O3/CNTs catalyst. Its SCR performance was studied and its structure and properties were analyzed. The effect of CNTs on the catalyst and its interaction with Fe2O3 were also discussed.(1) The preparation method of the catalyst is a crucial factor in determining its catalytic performance. Comparison of impregnation method, precipitation method and hydrothermal method, we found the catalyst prepared by the ethanol-impregnation method showed the best SCR activity, especially in the low temperature region. By further optimization of the catalyst components ratio and calcination temperature, we determined that the optimal component ratio is m(Fe(NO3)3-9H2O):m(CNTs)=4:1 and the optimum calcination temperature was 350℃.(2) The Fe2O3/CNTs catalyst prepared by the ethanol-impregnation method obtained excellent activity at low temperature. In the range of 200-325℃, more than 90% NOx conversion was obtained. At 250℃, maximum NOx conversion (96.6%) was obtained. In the whole testing range, N2 selectivity was maintained for more than 90%. The catalyst showed good resistance to sulfur, water resistance and stability. The addition of SO2 increased acidity on catalyst surface, improving the ability of NH3 adsorption and activation on the catalyst. (3) The studies found, ethanol was used as the solvent, which promoted the dispersion of CNTs. CNTs greatly increased the specific surface area and pore volume of Fe2O3, which promoted uniform and effective dispersion of a-Fe2O3 nanoparticles on the wall of CNTs. CNTs promoted the electronic transfer of Fe2O3, improving its redox property. This made catalysts exhibit excellent low-temperature activity.