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本文制备了一系列Fe-Mn/Al_2O_3催化剂,并在固定床上考察了其NH_3低温选择性催化还原NO的性能.首先考察了不同Fe负载量制备的催化剂的脱硝性能,优选出最佳的Fe负载量;在此基础上,研究了Mn负载量对催化剂脱硝效率的影响;最后,对优选催化剂的抗H_2O和抗SO_2性能进行了实验研究;同时,对催化剂由于SO_2所造成的失活机制进行了考察.采用N_2吸附-脱附、X射线衍射、透射电镜、能量弥散X射线谱、程序升温还原、程序升温脱附、X射线光电子能谱、热重和傅里叶变换红外光谱等方法对催化剂进行了表征.结果表明,最佳的Fe和Mn负载量均为8%,所制的8Fe-8Mn/Al_2O_3催化剂在150°C的脱硝效率可达近99%;同时,在整个低温测试区间(90–210°C)的脱硝效率均超过了92.6%.Fe在催化剂表面主要以Fe~(3+)形态存在,而Mn主要包括Mn~(4+)和Mn~(3+);Mn的添加提高了Fe在催化剂表面的积累,促进了催化剂比表面积增大和活性物种分散,改善了催化剂氧化还原性能和对NH_3的吸附能力.催化剂的高活性主要是由于其具有较大的比表面积、高度分散的活性物种、增加的还原特性和表面酸性、较低的结合能、较高的Mn~(4+)/Mn~(3+)和增强的表面吸附氧.此外,8Fe-8Mn/Al_2O_3的催化性能受H_2O和SO_2影响较小,抗H_2O和SO_2能力较强.同时,反应温度对催化剂的抗硫性有重要影响,在较低的反应温度下,催化剂抗硫性更好;SO_2造成催化剂活性降低主要是由于催化剂表面硫酸盐物种的生成.一方面,表面硫酸铵盐的生成造成催化剂孔道堵塞和比表面积降低,减少了反应中的气固接触从而导致活性降低;另一方面,催化剂表面的活性物种被硫酸化,造成反应中的有效活性位减少,从而降低了催化剂活性.
In this paper, a series of Fe-Mn / Al_2O_3 catalysts were prepared and the performance of selective catalytic reduction of NO with NH_3 at low temperature was investigated on a fixed bed.Firstly, the denitrification performance of catalysts prepared with different Fe loadings was investigated, and the optimum Fe loading On this basis, the effect of Mn loading on the denitrification efficiency of the catalyst was studied. Finally, the anti-H_2O and anti-SO_2 performance of the preferred catalysts were investigated. At the same time, the deactivation mechanism of the catalyst due to SO_2 The adsorption and desorption were investigated by N 2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, temperature programmed reduction, temperature programmed desorption, X-ray photoelectron spectroscopy, thermogravimetry and Fourier transform infrared spectroscopy The results show that the optimum loadings of Fe and Mn are both 8% and the efficiency of denitrification of the prepared 8Fe-8Mn / Al_2O_3 catalyst can reach nearly 99% at 150 ° C. In the meantime, 90-210 ° C), the denitrification efficiency exceeded 92.6% .Fe mainly existed in the form of Fe ~ (3+) on the surface of catalyst, while Mn mainly consisted of Mn ~ (4+) and Mn ~ (3 +); Mn Addition increases the accumulation of Fe on the catalyst surface, promoting the catalyst Increased surface area and dispersed active species, improved the redox performance of the catalyst and the adsorption capacity of NH 3 .The high activity of the catalyst is mainly due to its larger specific surface area, highly dispersed active species, increased reduction characteristics and surface acidity Low binding energies, higher Mn 4+ / Mn 3+ and enhanced surface adsorbed oxygen.In addition, the catalytic performance of 8Fe-8Mn / Al 2 O 3 was less affected by H 2 O and SO 2, The reaction temperature has an important influence on the anti-sulfur of the catalyst, and the anti-sulfur property of the catalyst is better at lower reaction temperature; the decrease of the catalyst activity caused by SO 2 is mainly caused by the formation of sulfate species on the catalyst surface. On the other hand, the active species on the surface of the catalyst are sulfated, resulting in the effective active sites in the reaction. On the other hand, the surface active species of the catalyst are sulfated, resulting in the blockage of the catalyst pore and the reduction of the specific surface area, thereby reducing the gas-solid contact in the reaction. Decrease, thus reducing the catalyst activity.