Mechanism of selective reduction of N_(2)O by CO over Fe-β catalysts studied by in-situ/operando spectroscopy  

一氧化碳在铁-β沸石催化剂上选择性还原N_(2)O机理的原位/Operando光谱研究

作　　者：Yucheng Qian Shunsaku Yasumura Ningqiang Zhang Akihiko Anzai Takashi Toyao Ken-ichi Shimizu 钱宇澄;Shunsaku Yasumura;张宁强;Akihiko Anzai;Takashi Toyao;Ken-ichi Shimizu(北海道大学催化研究所,日本札幌;东京大学工业科学研究所,日本东京)

机构地区：[1]Institute for Catalysis,Hokkaido University,N-21,W-10,Sapporo 001-0021,Japan [2]Institute of Industrial Science,The University of Tokyo,Komaba 4-6-1,Meguro,Tokyo 153-8505,Japan

出　　处：《Chinese Journal of Catalysis》2025年第2期185-192,共8页催化学报(英文)

摘　　要：Selective reduction of N_(2)O by CO under excess O_(2) was effectively catalyzed by Fe(0.9 wt%)-exchangedβzeolite(Fe0.9β)in the temperature range of 250–500°C.Kinetic experiments showed that the apparent activation energy for N_(2)O reduction with CO was lower than that for the direct N_(2)O decomposition,and the rate of N_(2)O reduction with CO at 300℃ was 16 times higher than that for direct N_(2)O decomposition.Reaction order analyses showed that CO and N_(2)O were involved in the kinetically important step,while O_(2) was not involved in the important step.At 300℃,the rate of CO oxidation with 0.1%N_(2)O was two times higher than that of CO oxidation with 10%O_(2).This quantitatively demonstrates the preferential oxidation of CO by N_(2)O under excess O_(2) over Fe0.9β.Operando/in-situ diffuse reflectance ultraviolet-visible spectroscopy showed a redox-based catalytic cycle;α-Fe-O species are reduced by CO to give CO_(2) and reduced Fe species,which are then re-oxidized by N_(2)O to regenerate theα-Fe-O species.The initial rate for the regeneration ofα-Fe-O species under 0.1%N_(2)O was four times higher than that under 10%O_(2).This result shows quantitative evidence on the higher reactivity of N_(2)O than O_(2) for the regeneration ofα-Fe-O intermediates,providing a fundamental reason why the Fe0.9βcatalyst selectively promotes the CO+N_(2)O reaction under excess O_(2) rather than the undesired side reaction of CO+O_(2).The mechanistic model was verified by the results of in-situ Fe K-edge X-ray absorption spectroscopy.随着温室气体排放的增加,N_(2)O作为一种具有高全球变暖潜力的温室气体,函需有效控制其排放.现有的N_(2)O分解技术虽能在无还原剂情况下将其分解,但由于需要高温条件且在过量氧气存在下效率较低,限制了其广泛应用.相比之下,使用CO作为还原剂进行选择性催化还原的反应温度低、低温活性好,有望成为一种更具N_(2)O去除效率的途径.然而,现有的非贵金属催化剂在氧气环境下活性较差.本文研究了铁交换沸石(Fe-β)催化剂在过量氧气条件下通过CO选择性还原N_(2)O的催化机理,揭示了铁在氧化还原循环中的状态变化,旨在为开发高效N_(2)O还原催化剂提供理论依据和实验数据支持.本文创新性的对Fe-β催化剂在过量氧气环境下促进N_(2)O选择还原反应的机理进行了系统研究.通过紫外-可见光谱(UV-vis)和X-射线吸收光谱(XAS)研究了Fe0.9β催化剂在250-500℃范围内CO还原N_(2)O的反应机理。结果发现,Fe0.9β催化剂表现出较好的催化性能,表观活化能为38kJ/mol,显著低于N_(2)0直接分解所需的99kJ/mol.在300℃下,N_(2)O还原速率比直接分解速率的16倍。此外,CO与N_(2)O的反应速率是CO与O_(2)反应速率的两倍,表明N_(2)O而非氧气在该催化反应中优先与CO发生反应.采用原位UV-vis光谱研究了N_(2)O选择还原反应的氧化还原循环机制:反应初始时,Fe(I)-αO物种被CO还原生成CO_(2)和Fe(II)物种,随后N_(2)O将Fe(II)物种重新氧化为Fe(III)-αO物种.实验结果表明,N_(2)O相较于O,在该循环中具有更高的反应活性.具体而言,尽管O_(2)的浓度是N_(2)O的100倍,N_(2)O氧化速率仍然是O_(2)的4倍,这表明了NO在Fe位点上的反应更为迅速。通过XAS光谱进一步确认了Fe在催化反应中的氧化态变化,证明了Fe在N_(2)O氧化过程中经历了Fe^(2+)与Fe^(3+)之间的氧化还原循环.TOF数据表明,低Fe含量催化剂Fe0.9β的单个Fe位点表现出更高的催化活性,这进一

关 键 词：Fe-exchanged zeolites N_(2)0 Selective catalytic reduction In-situ ultraviolet-visible 

分 类 号：O643.32[理学—物理化学] O643.3[理学—化学]