Preparation And Properties Of Iron-based Mixed Oxides For Selective Catalytic Reduction Of NO_x With NH₃

Nitrogen oxides (NOx) are a major source of air pollution and can cause a series ofenvironmental issues, such as acid rain, photochemical smog, ozone depletion and haze.Selective catalytic reduction (SCR) of NOxwith ammonia is the most effective and mostwidely used method, and the catalysts are the key of SCR technology. However, thetraditional vanadium-based catalysts would bring about some disadvantages, such as highdenitration temperature, high cost and the toxicity of vanadium pent-oxide. Therefore, it is ofgreat significance to develop novel SCR catalysts with high activity, low cost and absence oftoxicity. Despite of the lower activity at low temperature, iron-based catalysts have someadvantages with low cost and absence of toxicity and high resistance to H2O and SO2, and arepotential catalysts for SCR. In this paper, the novel iron-tungsten (Fe-W) mixed oxides andiron-molybdenum (Fe-Mo) mixed oxides were prepared by the modified co-precipitationmethod, and the influence of doped tungsten and molybdenum on the structure and SCRactivity of the mixed oxides were systematically investigated.A series of Fe-W mixed oxide catalysts were prepared by a modified co-precipitationmethod, and characterized by X-ray powder diffraction (XRD), N2adsorption-desorption,inductively coupled plasma atomic emission spectrometry (ICP-AES), scanning electronmicroscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure(XAFS), temperature programmed reduction (TPR) and temperature programmed desorption(TPD). The results show that there was a strong interaction between Fe and W, whichinhibited the crystallization of Fe2O3. A certain amount of doped tungsten also affected themorphology of the mixed oxides. The mixed oxides possessed a unique flower-like structurewhich consisted of nanosheets. The surface area and pore structure of the mixed oxides wereimproved by the doped tungsten. What’s more, the concentration of acid sites on the catalystsincreased. The SCR activities of the Fe-W mixed oxides were evaluated. It was found that thedoped W could greatly enhance the SCR activity with high N2selectivity and resistance toH2O and SO2.Fe-Mo mixed oxide catalysts were also prepared by the modified co-precipitation method.The results of characterization and SCR activity test indicated that the morphology of the mixed oxides possessed flocculent-like or sheet-like structure and the surface area of themixed oxides were larger than that of Fe2O3. The doped Mo could also enhance the SCRactivity with high N2selectivity and resistance to H2O and SO2.