In Situ/Operando Spectroscopic Studies on the NH3SCR Mechanism over Fe-Zeolites
In Situ/Operando Spectroscopic Studies on the NH3SCR Mechanism over Fe-Zeolites
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Fe-沸石上 NH3SCR 机理的原位/操作光谱研究
DOI：
10.1021/acscatal.2c02904
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发表时间：
2022
期刊：
影响因子：
12.9
通讯作者：
Shimizu Ken-ichi
中科院分区：
文献类型：
--
作者：
Yasumura Shunsaku;Qian Yucheng;Kato Taisetsu;Mine Shinya;Toyao Takashi;Maeno Zen;Shimizu Ken-ichi
采用原位/操作光谱（IR、UV-vis和Fe K边X射线吸收近边结构）和密度泛函理论（DFT）研究了300 ° C下Fe交换丝光沸石（莫尔）上NH3选择性催化还原NO（NH3-SCR）的还原/氧化半循环.不同的光谱结果表明，在还原半循环（NO + NH3）中，Fe 3+还原为Fe 2+，同时生成N2和H2O。在随后的氧化半循环（O2或NO + O2）中，Fe 2+被再氧化为Fe 3+。还原半周期包括几个基本步骤。在低温（<100 ° C）下观察到NO还原Fe 3 +-OH产生Fe 2+和NO+物质，而在随后的100 ° C下暴露于NH3下观察到由于NO+还原而形成N2。在瞬态条件下，当B-NH3覆盖度较低时，B-NH3上的NH3与NO反应生成N2，表明B-NH3不是NH3的旁观者，而是NH3的储存者.过渡态理论计算表明，Al位上的[Fe~（3+）（OH-）_2]~+与气态NO生成亚硝酸（HONO）中间体是一个容易的过程（Ea = 29.2kJ/mol）。结合实验观察和密度泛函理论计算，提出了Fe-沸石上还原半循环的机理：[Fe 3+（OH-）2]+被NO还原生成HONO中间体，HONO中间体再与Brønsted酸中心上的NH3反应，通过NO+生成H2O和N2.基于上述机理见解，测试了具有不同Fe负载量和Si/Al比的Fe-沸石（莫尔和β）用于NH3-SCR反应。因此，具有相对大量布朗斯台德酸位（富含Al的β，Si/Al比为5）的2.7wt% Fe负载沸石在低温区域显示出最高的NOx转化率。
Reduction/oxidation half-cycles of the selective catalytic reduction of NO with NH3(NH3–SCR) over Fe-exchanged mordenite (MOR) zeolites at 300 °C were investigated byin situ/operandospectroscopy (infrared, UV–vis, and Fe K-edge X-ray absorption near edge structure) and density functional theory (DFT) calculation. The reduction of Fe3+into Fe2+and the simultaneous formation of N2and H2O in the reduction half-cycle (under NO + NH3) were demonstrated by different spectroscopic results. In the subsequent oxidation half-cycle (under O2or NO + O2), Fe2+was reoxidized into Fe3+. The reduction half-cycle comprises several elementary steps. Reduction of Fe3+–OH by NO producing Fe2+and NO+species was observed at low temperatures (<100 °C), while N2formation due to the reduction of NO+was observed under subsequent NH3exposure at 100 °C. Under transient conditions, NH3on Brønsted acid sites (B–NH3) reacted with NO to generate N2when the coverage of B–NH3was low, indicating that B–NH3is not a spectator but a reservoir of NH3. Transition state calculation theoretically suggested that the formation of nitrous acid (HONO) intermediates from [Fe3+(OH–)2]+at a Al site and gaseous NO was a facile process (Ea= 29.2 kJ/mol). Combining the experimental observation and DFT calculation, the mechanism of the reduction half-cycle over Fe–zeolites was proposed; [Fe3+(OH–)2]+is reduced by NO to produce a HONO intermediate, which then reacts with NH3on Brønsted acid sites to yield H2O and N2via NO+species. Based on the mechanistic insights above, Fe–zeolites (MOR and β) with different Fe loadings and Si/Al ratios were tested for NH3–SCR reaction. Consequently, 2.7 wt % Fe-loaded zeolites with a relatively large number of Brønsted acid sites (Al-rich β with a Si/Al ratio of 5) showed the highest NOxconversion in a low-temperature region.