Selective catalytic reduction of NO_x with methanol over supported silver catalysts

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• 作者：Marika M&auml ; nnikkö ; ; ^{marika.mannikko@chalmers.se} ; Magnus Skoglundh ; Hanna H&auml ; relind Ingelsten
• 关键词：Silver/alumina ; Silver/ZSM-5 ; Methanol-SCR ; Lean NOx reduction ; Hydrogen
• 刊名：Applied Catalysis B ; Environmental
• 出版年：2012
• 期刊代码：4_09263373
• 类别：ce
• 出版时间：30 May, 2012
• 卷：119-120
• 期：Complete
• 页码：256-266
• 文件大小：1784 K

摘要

Methanol is a potential renewable fuel for the transport sector and is thus interesting to study as reducing agent for NO_x in hydrocarbon assisted selective catalytic reduction (HC-SCR). The effect of catalyst composition on the lean NO_x reduction during methanol-SCR conditions was investigated. In particular silver supported on alumina and ZSM-5 were in focus and parameters that can improve the NO_x reduction performance, i.e. the C/N molar ratio and the addition of hydrogen, were specifically studied. Five catalysts were prepared (H-ZSM-5, Ag/H-ZSM-5, Pd/Ag/H-ZSM-5, 纬-Al₂O₃ and Ag-Al₂O₃) and compared in flow reactor experiments. The Ag-Al₂O₃ (2 wt%Ag, sol-gel) sample was found to give higher NO_x reduction compared to the other tested samples, where important factors are suggested to be the support material, the preparation method and the Ag loading. The NO_x reduction over Ag-Al₂O₃ with methanol is proposed to proceed by adsorbed nitrates or nitrites (or gas phase NO₂) reacting with adsorbed acetate or formaldehyde like species forming adsorbed RNO₂ or RONO, with subsequent conversion into NCO, CN, RNH₂ or NH₃, with final desorption of N₂ and CO_x (or HCHO). The addition of hydrogen and an increase of the supplied methanol concentration resulted in an increased NO_x reduction mainly over the Ag-Al₂O₃ sample, where the addition of hydrogen also extended the active temperature interval towards lower temperatures. Another effect of the addition of hydrogen was formation of more oxidized carbon containing reaction products. The Ag-Al₂O₃ catalyst prepared by the sol-gel method, including freeze-drying of the formed gel, is concluded to be the most promising candidate of the tested catalysts for methanol-SCR.