CaCl2改性选择性催化还原催化剂氧化汞的实验与机理研究
Experimental and Mechanism Study on Mercury Oxidation by Selective Catalytic Reduction Catalyst Modified by Calcium Chloride
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摘要: 基于选择性催化还原(selective catalytic reduction,SCR)催化剂对单质汞的氧化受煤中氯含量的限制,提出利用氯化钙改性SCR催化剂促进单质汞的氧化。在固定床实验台上研究了不同氯化钙添加量下SCR催化剂对单质汞的氧化性能,进而利用基于密度泛函的理论方法计算了单质汞在催化剂以及改性后的催化剂表面的吸附行为。结果表明,单独的SCR催化剂对单质汞的氧化效果很小,氧化效率仅为7%,添加1%的氯化钙后氧化效率提高到79%。进一步的理论计算表明,氯化钙中的氯容易与V2O5表面的氧结合,起到改性SCR催化剂的作用,而Hg0在改性后的V2O5表面可以生成稳定的HgCl,其中HgCl一部分脱附到烟气中,一部分吸附在催化剂表面,有利于单质汞的氧化。Abstract: As the oxidation of Hg0 by selective catalytic reduction（SCR） catalyst is restricted by the content chlorine in coal, the method using calcium chloride to modify SCR catalyst in order to improve the oxidation of elemental mercury was proposed. The influence of SCR catalyst containing different amount of calcium chloride on the oxidation of Hg0 was investigated experimentally. Adsorption behaviors of Hg0 on the surface of catalyst and modified-catalyst were calculated based on the density functional theory. The results show: Only 7 % of Hg0 can be oxidized with SCR catalyst, while 79 % can be oxidized with 1% calcium chloride addition. A further calculation indicates that the chloride in calcium chloride can combine with the oxygen on the surface of the V2O5 forming active sites, and Hg0 adsorbs on chlorine-modified V2O5 surface forming HgCl which escapes to the flue gas or strongly adsorbs on V2O5 surface, which helps the oxidation of Hg0.
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