Xiao Peipei, Wang Lizhuo, Toyoda Hiroto, Wang Yong, Nakamura Kengo, Huang Jun, Osuga Ryota, Nishibori Maiko, Gies Hermann, Yokoi Toshiyuki
Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.
School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, New South Wales 2006, Australia.
J Am Chem Soc. 2024 Nov 20;146(46):31969-31981. doi: 10.1021/jacs.4c11773. Epub 2024 Nov 5.
Fe-containing zeolites are effective catalysts in converting the greenhouse gases CH and NO into valuable chemicals. However, the activities of Fe-containing zeolites in methane conversion and NO decomposition are frequently conflated, and the activities of different Fe species are still controversial. Herein, Fe-containing aluminosilicate CHA zeolites with Fe species at different spatial distances affected by the arrangement of framework Al atoms were synthesized in a one-pot manner in the presence or absence of Na. The arrangement of framework Al atoms was identified by Al and Si MAS NMR spectra and thermogravimetry-differential thermal analysis (TG-DTA) curves. Ultraviolet (UV)-vis, X-ray absorption spectroscopy (XAS), and NO adsorption fourier transform infrared spectroscopy (FTIR) spectra were adopted to analyze Fe speciation. The higher proportion of Fe species in the 6 MR of Fe-CHA zeolites in the presence of Na was confirmed by the NO adsorption FTIR spectrum. The activities of proximal and distant Fe sites in reactions including direct oxidation of methane to methanol, methanol to hydrocarbon, and NO decomposition were compared at different temperatures to provide the corresponding active sites and reaction pathways. The distant, isolated Fe and isolated proton were more active in the direct oxidation of methane to methanol and tandem conversion of methanol to hydrocarbon reactions than the proximal, isolated Fe and paired protons, respectively. Additionally, proximal, isolated Fe sites afforded higher activity in NO decomposition. These findings guide the design of highly active catalysts in methane oxidation, methanol to hydrocarbon, and NO decomposition reactions, addressing energy and environmental concerns.
含铁沸石是将温室气体CH和NO转化为有价值化学品的有效催化剂。然而，含铁沸石在甲烷转化和NO分解中的活性常常被混淆，并且不同铁物种的活性仍存在争议。在此，在有或没有Na存在的情况下，以一锅法合成了具有受骨架Al原子排列影响的不同空间距离的铁物种的含铁铝硅酸盐CHA沸石。通过Al和Si MAS NMR光谱以及热重-差热分析（TG-DTA）曲线确定了骨架Al原子的排列。采用紫外（UV）-可见光谱、X射线吸收光谱（XAS）和NO吸附傅里叶变换红外光谱（FTIR）光谱来分析铁的形态。通过NO吸附FTIR光谱证实了在有Na存在的情况下，Fe-CHA沸石的6元环中Fe物种的比例更高。在不同温度下比较了近端和远端Fe位点在包括甲烷直接氧化为甲醇、甲醇转化为烃以及NO分解等反应中的活性，以提供相应的活性位点和反应途径。远端、孤立的Fe和孤立的质子在甲烷直接氧化为甲醇以及甲醇串联转化为烃反应中分别比近端、孤立的Fe和成对的质子更具活性。此外，近端、孤立的Fe位点在NO分解中具有更高的活性。这些发现指导了在甲烷氧化、甲醇转化为烃以及NO分解反应中高活性催化剂的设计，解决了能源和环境问题。
