具有高效单质汞氧化性能SCR催化剂的制备及表征
发布时间：2018-10-05 07:45
【摘要】：汞单质及其化合物排放到空气中会造成严重的环境污染,燃煤烟气汞排放受到全球广泛关注。燃煤烟气中汞的形态有三种:单质汞(Hg0)、氧化态汞(Hg2+)和颗粒态汞(Hgp),其中的Hg0很难被现有空气污染物控制装置脱除,从而会通过烟囱直接排入大气中。研究发现,燃煤电厂用来烟气脱硝的SCR催化剂可一定程度上催化氧化烟气中的Hg0,气态氧化汞可在湿法脱硫系统中被吸收,两者实现了对烟气中Hg元素的协同脱除。为了在不影响SCR催化剂脱硝性能的同时提高其汞氧化效率,可以选择对传统SCR催化剂进行改性。本文采用湿混法制备了CuCl2改性SCR催化剂,并在催化剂性能评价实验台上,模拟烟气组分,在不同温度下测试单质汞的催化氧化效率。基于性能评价实验结果、XRD、BET、XRF、XPS等表征手段,结合化学吸附、程序升温还原实验,探讨改性SCR催化剂的氧化还原能力、酸碱位、比表面积以及组分含量等,分析改性催化剂对单质汞催化氧化作用的可能机制,为优化改性催化剂性能提供理论支持。研究结果表明,在固定比例的模拟烟气工况下,随着温度的提高,单质汞催化氧化效率呈现先升后降的趋势,改性前后SCR催化剂在350℃下的汞催化氧化效率均达到最高。研究发现,CuCl2的掺杂有效地增加了催化剂的酸性位点,这对提高其脱硝活性有一定的意义,改性后SCR催化剂的氧化还原性能较改性前有一定幅度的增强,结合活性评价结果,可以认为SCR催化剂对单质汞的催化活性与其还原性有关。SCR催化剂元素分析结果显示,改性SCR催化剂中Cu元素主要以Cu2+的形式存在,在性能测试后,Cu2+含量减少,相应的低价态Cu元素比例增大,而且反应后催化剂中晶格氧被消耗,相应的化学吸附氧比例增大,说明在反应过程中Cu和O均参与了电子转移。根据性能实验和表征结果分析,改性SCR催化剂对单质汞的催化氧化机理符合Mars-Maessen机理。
[Abstract]:The emission of mercury and its compounds into the air will cause serious environmental pollution, and mercury emissions from coal-fired flue gas have attracted worldwide attention. There are three forms of mercury in coal-fired flue gas: elemental mercury (Hg0), oxidized mercury (Hg2) and particulate mercury (Hgp), the Hg0 of which is difficult to be removed by the existing air pollutant control devices, which will be discharged directly into the atmosphere through the chimney. It is found that the SCR catalyst used for flue gas denitrification in coal-fired power plants can be used to catalyze the oxidation of Hg0, gaseous mercury oxide in flue gas to a certain extent and can be absorbed in the wet desulfurization system. The two catalysts can achieve the synergistic removal of Hg elements in flue gas. In order to improve the mercury oxidation efficiency of SCR catalyst without affecting its denitrification performance, the traditional SCR catalyst can be modified. In this paper, CuCl2 modified SCR catalyst was prepared by wet mixing method. The catalytic oxidation efficiency of elemental mercury was measured at different temperatures on the catalyst performance evaluation bench. Based on the experimental results of performance evaluation, the redox ability, acid and base sites, specific surface area and component content of modified SCR catalysts were investigated by means of chemical adsorption and temperature programmed reduction experiments. The possible mechanism of the catalytic oxidation of elemental mercury over modified catalysts is analyzed, which provides theoretical support for optimizing the performance of the modified catalysts. The results showed that the catalytic oxidation efficiency of mercury increased first and then decreased with the increase of temperature under the condition of fixed proportion of simulated flue gas. The catalytic oxidation efficiency of SCR catalyst reached the highest at 350 鈩，
本文编号：2252570
[Abstract]:The emission of mercury and its compounds into the air will cause serious environmental pollution, and mercury emissions from coal-fired flue gas have attracted worldwide attention. There are three forms of mercury in coal-fired flue gas: elemental mercury (Hg0), oxidized mercury (Hg2) and particulate mercury (Hgp), the Hg0 of which is difficult to be removed by the existing air pollutant control devices, which will be discharged directly into the atmosphere through the chimney. It is found that the SCR catalyst used for flue gas denitrification in coal-fired power plants can be used to catalyze the oxidation of Hg0, gaseous mercury oxide in flue gas to a certain extent and can be absorbed in the wet desulfurization system. The two catalysts can achieve the synergistic removal of Hg elements in flue gas. In order to improve the mercury oxidation efficiency of SCR catalyst without affecting its denitrification performance, the traditional SCR catalyst can be modified. In this paper, CuCl2 modified SCR catalyst was prepared by wet mixing method. The catalytic oxidation efficiency of elemental mercury was measured at different temperatures on the catalyst performance evaluation bench. Based on the experimental results of performance evaluation, the redox ability, acid and base sites, specific surface area and component content of modified SCR catalysts were investigated by means of chemical adsorption and temperature programmed reduction experiments. The possible mechanism of the catalytic oxidation of elemental mercury over modified catalysts is analyzed, which provides theoretical support for optimizing the performance of the modified catalysts. The results showed that the catalytic oxidation efficiency of mercury increased first and then decreased with the increase of temperature under the condition of fixed proportion of simulated flue gas. The catalytic oxidation efficiency of SCR catalyst reached the highest at 350 鈩，
本文编号：2252570
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