| Coal resources are very rich in our country, and coal is dominated in the energy structure of China. Coal-fired power plants and other stationary sources are the main source of coal consumption. The combustion of coal will produce much nitrogen compounds and sulfur compounds and other pollutants. Thus, how to control and governance stationary source exhaust pollution has attracted many attention of scientists. The sulfide governance from exhausts have made a good achievement in China, however, the control of nitrogen oxides starts relatively late, and it is also an urgent problem need to be resolved. The selective catalytic reduction is a mainstream technology for denitration by ammonia from the stationary sources at present. While V2O5-WO3(MoO3)/TiO2 catalysts are commonly used in denitration of stationary sources in industry. However, there are some shortcomings:such as the narrow operating temperature window, easier to be poisonous and the short longlife of this catalyst and the vanadium species are poisonous.It is required to develop the low-temperature denitration catalyst or a non-vanadium-based catalysts with a wide operating temperature window. Manganese-based catalysts have the best low-temperature active among the transition metal oxides, thus it is present research focus at low-temperature denitration. The anatase TiO2 carrier is easier to form the strong interaction with active ingredients, the better water resistance and sulfur tolerance, as well as readily available and inexpensive, etc.Thus it is widely used in industry. However, the crystal transformation process from anatase to rutile will be produced when the manganese-based catalyst and anatase TiO2 are combinated for the induced effects, regardness of impregnation or co-precipitation methods. And thus reduces the catalytic performance. We attempts to suppress the transformation of TiO2 phase by steric hindrance of cationic surfactants during the preparation of catalysts.A series of FeMnTiOx mixed oxides catalysts, which were synthesized with CTAB-assisted by co-precipitation method and calcined at different temperatures, were investigated for selective catalytic reduction of NO with NH3 in the presence of excess O2. The obtained samples were characterized and measured by means of N2-physisorption, XRD, TEM, H2-TPR, XPS, NH3-TPD, and in situ DRIFTS technologies. Exploring the mechanism of CTAB-assisted in ammonia selective catalytic reduction reaction, and the calcination temperature and different ratio of raw materials impact on catalytic properties. Specific contents are as follows:1. Comparing the sample prepared with CTAB and the sample prepared without CTAB, the results indicates that the addition of CTAB can suppress the transformationof TiO2 phase from anatase to rutile by steric hindrance during the preparation of catalysts, and enhance the interaction between the support and active ingredients, and thus enhance the redox properties of samples; Improve the formation of more Lewis acid sites on the surface of samples, it can therefore improve the catalytic performance. The catalyst obtained at 500℃ in present work shows nearly 100% NO conversion at 100-350℃, more than 80% N2 selectivity at 75-200℃, and excellent H2O durability for the selective catalytic reduction of NO by NH3 with a space velocity of 30000 mL·g-1·h-1. And it exhibited water resistance to a certain extent.2. Different calcination temperatures were employed to prepare samples and investigate catalytic performance in NH3-SCR reaction. In order to further investigate the effect of CTAB on the catalytic properties, the sample prepared without CTAB was used to compare. The results indicate that the NO conversion is not predominately controlled by specific area. Compared with amorphous TiO2, the anatase TiO2 crystalline phase is more conducive to enhance the electron interaction between manganese species and support. The binding energy of lattice oxygen is connection with the activated of NH3 in reaction. These features was helpful to improve the low-temperature activity of the sample. The CTAB-assisted was beneficial for the formation of isolated state active phase for the steric effect. While the isolated state of iron species beneficial to decompose N2O, which could improve the N2 selectivity in NH3-SCR.The calcination temperature had a great influence on the structure of support and valence state of manganese species, as well as the dispersion extent of active phase on the surface of samples. The sample calcined at 400℃ showed excellent low-temperature activity and mid-temperature N2 selectivity. The NO conversion and N2 selectivity of this sample were above 90% in the range of 150-350℃ at a space velocity of 30,000 mL·g-1·h-1. Furthermore, it exhibited sulfur tolerance and water resistance to a certain extent. It not only expands the operating temperature window but also avoids the use of vanadium-based catalysts. The results showed that the sample is a promising industrial catalyst applied in mid-low temperature NH3-SCR reaction.3. Studied the effects of different ratio of raw materials on the catalytic performance, the results showed that:when the molar ratio of Fe, Mn, Ti species in 1: 1:10, the low-temperaure activity in NH3-SCR reaction is best. While the Selectively of samples in NH3-SCR reaction is related with iron content. |
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