摘要/Abstract

采用后合成修饰法成功制备出一系列双金属Ag_x-Ni-MOF-74催化剂, 并应用于CO选择性催化还原NO (CO-SCR)反应. 研究结果发现, 相较于单金属Ni-MOF-74催化剂, 双金属Ag-Ni-MOF-74具有更加优良的低温CO催化还原NO能力, 其中Ag₁-Ni-MOF-74催化剂在200~300 ℃的温度范围达到接近100% NO转化率. 利用X射线衍射分析(XRD)、傅氏转换红外线光谱分析(FT-IR)、场发射扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、氢气程序升温还原性能测试(H₂-TPR)等技术对样品的结构和性能进行了探究, 发现Ag的加入有利于丰富催化剂活性位点和提高催化剂的比表面积, 并促进反应物的有效活化和传输. 此外, 基于原位红外光谱分析, 发现了CO-SCR反应过程遵循具有较高低温催化效率的Langmuir-Hinshelwood (L-H)机理.
关键词: 脱硝, 双金属有机骨架, Ag-Ni-MOF-74, 后合成修饰法, CO选择性催化还原NO (CO-SCR)
Selective catalytic reduction of NO_x with CO technology (CO-SCR) is supposed to be a cost-effective and environmentally friendly technique for NO_x abatement in the flue gas under CO-rich conditions. As a promising class of porous hybrid inorganic-organic materials, bimetallic metal-organic frameworks exhibit great physicochemical properties in catalysis area, whereas their application in low-temperature CO-SCR system are seldom reported. In this study, a series of bimetal organic-frameworks catalysts with different Ag contents were successfully prepared by a post-synthesis method and were assessed for NO reduction by CO. The typical experimental procedure for the synthesis of bimetallic Ag-Ni-MOF-74 catalysts is as follows: First, a light yellow Ni-MOF-74 sample was prepared by a hydrothermal method. Then 250 mg Ni-MOF-74, 1 mmol of NaBH₄ and AgNO₃ with different molar ratio (0.25, 0.5, 1 mmol) were added into 40 mL N,N-dimethylformamide (DMF) solution, and were stirred for 6 h. The mixtures were further moved into a Teflon-lined autoclave at 150 ℃ for 12 h. After washing with DMF and methanol, the obtained Ag_x-Ni-MOF-74 catalysts were dried at 60 ℃ under vacuum for 12 h. Totally, bimetallic Ag-Ni-MOF-74 catalysts exhibited a better low-temperature CO-SCR efficiency than monometallic Ni-MOF-74 catalysts. Especially, Ag₁-Ni-MOF-74 achieved a nearly 100% NO conversion in the temperature range from 200 ℃ to 300 ℃. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and hydrogen temperature programmed reduction (H₂-TPR) techniques were used to investigate the structure and properties of the samples. It was found that Ag addition not only enriched the form of more active sites, but also increased the specific surface area of the catalysts, which promote the activation and transfer of reactants. The synergistic effect between Ag and Ni species also contributed to enhancement of surface oxygen vacancies and accelerated the electron transfer in NO+CO reaction. By combining XPS and in situ FT-IR results, the mechanism of CO-SCR reaction over Ag-Ni-MOF-74 was proposed to follow Langmuir- Hinshelwood (L-H) mechanism, which exhibits a more readily low-temperature reaction rate and a lower reaction barrier than Eley-Rideal (E-R) mechanism.
Key words: denitration, bimetallic MOFs, Ag-Ni-MOF-74, post synthetic modification, CO-SCR


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