碳氢化合物广泛存在于贫燃发动机尾气中,且原料易得无污染,以碳氢化合物为还原剂选择性催化还原NOx在富氧汽车尾气处理上具有一定的现实意义和应用前景。金属负载分子筛脱除NOx具有活性高及对环境友好等优点。本文综述了Fe、Co、In、Mn、Pd等非Cu基金属负载分子筛上碳氢化合物选择性催化还原NOx反应机理和催化剂性能等方面的研究进展,并在归纳和总结已有研究成果的基础上展望了非Cu基负载分子筛的研究发展趋势。依据负载金属、分子筛和还原剂不同,碳氢化合物选择性催化还原氮氧化物的活性位和反应中间体也各不相同,以丙烷为还原剂时Fe-ZSM-5分子筛是通过孤立的Fe2+与Fe3+之间的价态变化来脱除氮氧化物,而以甲烷为还原剂时Fe-AlPO-5分子筛则是以孤立的Fe3+和低聚态的FexOy物种为活性位。甲烷广泛存在于贫燃发动机尾气中,是脱除氮氧化物的较佳还原剂,而乙烯和丙烷等烃类由于其还原温度低于甲烷也得到较多研究。对其反应机理的研究有助于寻找影响反应的关键因素从而改善催化剂性能。根据所负载金属、分子筛和还原剂的特点,可优化出高效且环境友好的脱硝催化剂体系。
Selective catalytic reduction of condition has been widely studied for its potential NOx with hydrocarbons (CH-SCR-NOx ) under oxygen-rich to clean up exhausts from lean-burn engines. Hydrocarbons are readily available reducing agents which can provide non-polluting processes. The research advances in reaction mechanism of selective catalytic reduction of NOx by hydrocarbons and the properties of copper-free metal ( Fe, Co, In, Mn, Pd, etc. ) catalysts have been reviewed in this article. The technical trends of copper-free metal supported zeolite are prospected. The supported metal, the zeolite and the reductant correspond to their own active sites. The active sites of selective catalytic reduction of NOx with propane on Fe-ZSM-5 zeolite are isolated Fe2 + and Fe3 + , yet the active sites are isolated Fe3+ and oligonuclear FexOy on Fe-A1PO-5 zeolite with methane as reductant. Methane which is the preferred catalyst for removing nitrogen oxides is present in almost all combustion exhausts, while hydrocarbons such as ethene and propane have also been extensively studied due to their lower reduction temperature. The formation of key intermediates such as isocyanate and cyanide species is a necessary process during catalytic reaction. Study on reaction mechanism can help us to identify the key factors that influence the reaction and then optimize the catalytic processes. Efficient and environmentally friendly denitration catalyst system can be developed according to the specific characteristics of the supported metal, the zeolite and the reductant.