铈改性增强OMS-2汞氧化催化剂抗硫性能的机理研究

Mechanism for the enhancement of the resistance of the OMS-2 mercury oxidation catalyst to sulfur by modifying with cerium

针对氧化锰八面体分子筛(OMS-2)在催化氧化单质汞过程中抗硫性能差的问题,采用铈(Ce)对OMS-2催化剂进行改性提高其抗硫性。通过热力学分析、固定床实验、氮吸附、XRD、ICP和XPS等表征手段,研究了铈增强OMS-2抗硫能力的原因。结果表明,Ce改性得到的催化剂比表面积大、空隙结构丰富,可以在催化剂表面通过化学吸附吸附更多的Hg 0;Ce改性得到的催化剂会造成Mn缺陷生成,提高电子迁移率,使得吸附氧(Oβ)占比高,可提供更多的活性位点;OMS-2催化剂表面氧化的HgO可经不同浓度的SO 2还原为Hg 0或者HgSO 4,但Ce改性得到的催化剂可使该部分还原产物迅速重新氧化成HgO,提高了表观Hg 0氧化效率。该研究结果可为开发高性能抗硫汞氧化催化剂提供理论依据。

In view of the poor resistance of manganese oxide octahedral molecular sieve(OMS-2)catalyst to sulfur in the oxidation of elemental mercury,CeO 2 was used to modify the OMS-2 catalyst.The mechanism for the enhancement of the resistance of the OMS-2 catalyst to sulfur by modifying with CeO 2 was investigated,with the help of thermodynamic analysis,fixed-bed reaction test and various characterization methods like nitrogen sorption,XRD ICP and XPS.The results indicate:The OMS-2 catalyst modified by Ce has a large surface area and void-rich structure,which can adsorb more Hg 0 through chemical adsorption;More Mn defects are formed on the OMS-2 catalyst through modifying with Ce,leading to an increase in the electron mobility,the proportion of adsorbed oxygen(Oβ)species,and the density of catalytically active sites;The Ce-modified OMS-2 catalyst can quickly re-oxidize the reduced Hg 0 or HgSO 4 species(facilely formed on the pristine OMS-2 catalyst surface in the presence of SO 2)to HgO,which can then improve the apparent Hg 0 oxidation efficiency.The results should be helpful for the development of high-performance anti-thio catalysts for mercury oxidation.