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NOx是大气污染物的重要组成部分,能够造成酸雨、光化学烟雾和臭氧层破坏等一系列环境问题,严重危害人类健康.选择性催化还原(SCR)是控制NOx排放的主要技术,当前工业上普遍采用的是钒钛催化剂,然而该催化剂活性温度窗口较窄(300-400 ℃),N_2选择性较低,而且钒物种本身有毒.因此开发新型SCR催化剂成为研究热点.Fe/TiO_2催化剂具有稳定的化学性质,环境污染少且价格低廉,近年来受到广泛关注.为了提高Fe/TiO_2催化活性,人们采用了各种不同的制备方法.本文以F127作为结构导向剂,结合溶胶-凝胶法原位合成了具有介孔结构、工作温度在150-300 ℃的Fe/TiO_2脱硝催化剂,并与普通浸渍法和共沉淀法制备的催化剂进行了对比.利用N_2吸附脱附、紫外-可见光谱、X射线电子能谱、NH_3程序升温脱附和原位红外光谱等技术研究了制备方法对Fe/TiO_2催化剂物理结构及脱硝性能的影响.结果表明,相较于浸渍法和共沉淀法,模板法制备的催化剂具有较高的脱硝效率和抗H_2O和SO_2性能.作为结构导向剂,F127能够诱导催化剂形成均匀的介孔结构,有利于提高催化剂比表面积,促进反应物分子的扩散和转移,从而提高催化剂脱硝效率.进一步研究发现,模板法能够明显促进活性组分Fe物种的分散和NH_3吸附,载体与活性组分具有较强的相互作用,因而有利于催化剂产生较多的活性位.结合XPS结果,较多的活性位点有利于表面吸附氧(O_α)在催化剂表面的吸附.Oα有利于NO到NO_2的转化,从而促进快速SCR反应:NO+NO_2+2NH_3→2N_2+3H_2O.通过原位红外机理分析证明,吸附在模板法制备的催化剂表面的NO物种具有较强的稳定性,当温度超过200 ℃时,仍然保持一定的吸附强度;吸附NH_3红外结果表明,Lewis酸性位比Br?nsted酸性位具有更强的稳定性,当温度超过150℃仍然具有较强的Lewis酸吸附.催化剂表面稳定的NO物种和Lewis酸位上强的NH_3吸附是催化剂催化活性增加的重要原因.
NOx is an important part of air pollutants and can cause a series of environmental problems, such as acid rain, photochemical smog and ozone depletion, which seriously endanger human health.Selective catalytic reduction (SCR) is the main technology to control NOx emissions and is widely used in industry at present However, the activity temperature window is narrow (300-400 ℃), the N 2 selectivity is low and the vanadium species itself is toxic, so the development of a new type of SCR catalyst has become a research hotspot.Fe / TiO 2 catalyst has a stable chemical Nature, environmental pollution and low price, and has been widely concerned in recent years.In order to improve the catalytic activity of Fe / TiO 2, a variety of preparation methods have been adopted.In this paper, F127 was used as a structure-directing agent and synthesized in situ by sol-gel method The mesoporous structure of Fe / TiO 2 denitrification catalyst with mesoporous structure and working temperature of 150-300 ℃ was compared with that prepared by common impregnation method and coprecipitation method.Using N 2 adsorption and desorption, UV-Vis, X-ray electron Energy spectrum, NH_3 temperature-programmed desorption and in-situ infrared spectroscopy were used to study the effect of preparation methods on the physical structure and denitration performance of Fe / TiO_2 catalysts The results showed that compared with the impregnation method and coprecipitation method, the catalyst prepared by the template method has high denitrification efficiency and anti-H_2O and SO_2 performance as a structure-directing agent, F127 can induce the catalyst to form a uniform mesoporous structure, is conducive to Improve the specific surface area of the catalyst and promote the diffusion and transfer of the reactant molecules to improve the denitrification efficiency of the catalyst.Further study found that the template method can significantly promote the dispersion of the active component Fe species and NH 3 adsorption, the carrier and the active component have a strong mutual Which is in favor of the catalyst to produce more active sites.According to XPS results, more active sites are conducive to the adsorption of surface oxygen (O_α) on the catalyst surface.Oα is conducive to the conversion of NO to NO_2, thus promoting the rapid SCR Reaction: NO + NO_2 + 2NH_3 → 2N_2 + 3H_2O. The in-situ infrared mechanism analysis showed that the NO species adsorbed on the surface of the catalyst prepared by the template method has a strong stability. When the temperature exceeds 200 ℃, it still retains some adsorption The results of adsorption of NH_3 showed that Lewis acid sites have stronger stability than Br? Nsted sites and still have strong Lewis acid absorption Adsorption of surface-stable NO species on the catalyst and strong NH 3 adsorption on Lewis acid sites are important reasons for the increased catalytic activity of the catalyst.