Grzybek Justyna, Gil Barbara, Roth Wieslaw J, Skoczek Monika, Kowalczyk Andrzej, Chmielarz Lucjan
Faculty of Chemistry, Jagiellonian University in Kraków, Gronostajowa 2, 30-387 Kraków, Poland.
Faculty of Chemistry, Jagiellonian University in Kraków, Gronostajowa 2, 30-387 Kraków, Poland.
Spectrochim Acta A Mol Biomol Spectrosc. 2018 May 5;196:281-288. doi: 10.1016/j.saa.2018.02.033. Epub 2018 Feb 12.
Two-step preparation of iron and cobalt-containing MCM-56 zeolites has been undertaken to evaluate the influence of their physicochemical properties in the selective catalytic reduction (NH-SCR or DeNOx) of NO using NH as a reductant. Zeolites were prepared by the selective leaching of the framework cations by concentrated HNO solution and NHF/HF mixture and consecutively, introduction of Co and Fe heteroatoms, in quantities below 1wt%. Further calcination allowed to obtain highly dispersed active species. Their evaluation and speciation was realized by adsorption of pyridine and NO, followed by FTIR spectroscopy. Both Fe-MCM-56 zeolites showed excellent activities (maximum NO conversion 92%) with high selectivity to dinitrogen (above 99%) in the high temperature NH-SCR process. High catalytic activity of Fe-MCM-56 zeolites was assigned to the formation of stable nitrates, delivering NO to react with NH at higher temperatures and suppressing the direct NO oxidation. It was found that more nitrates was formed in Fe-MCM-56 (HNO) than in Fe-MCM-56 (HF/NHF) and that could compensate for the lower Fe loading, resulting in very similar catalytic activity of both catalysts. At the same time both Co-and Fe-MCM-56 zeolites were moderately active in direct NO decomposition, with maximum NO conversion not higher than 80% and activity window starting at 500°C. This phenomenon was expected since both types of catalysts contained well dispersed active centers, not beneficial for this reaction.
已采用两步法制备含铁和钴的MCM-56沸石，以评估其物理化学性质对使用NH作为还原剂的NO选择性催化还原（NH-SCR或DeNOx）的影响。通过用浓HNO溶液和NHF/HF混合物选择性浸出骨架阳离子，然后引入含量低于1wt%的Co和Fe杂原子来制备沸石。进一步煅烧可获得高度分散的活性物种。通过吡啶和NO的吸附，随后进行傅里叶变换红外光谱（FTIR）对其进行评估和形态分析。在高温NH-SCR过程中，两种Fe-MCM-56沸石均表现出优异的活性（最大NO转化率92%），对氮气具有高选择性（高于99%）。Fe-MCM-56沸石的高催化活性归因于稳定硝酸盐的形成，在较高温度下将NO输送与NH反应，并抑制NO的直接氧化。发现Fe-MCM-56（HNO）中形成的硝酸盐比Fe-MCM-56（HF/NHF）中更多，这可以弥补较低的Fe负载量，导致两种催化剂的催化活性非常相似。同时，Co-MCM-56和Fe-MCM-56沸石在直接NO分解中均具有中等活性，最大NO转化率不高于80%，活性窗口从500°C开始。由于两种类型的催化剂都含有分散良好的活性中心，对该反应不利，因此出现这种现象是可以预料的。
