催化学报 ›› 2022, Vol. 43 ›› Issue (8): 2001-2009.DOI: 10.1016/S1872-2067(21)64054-8

• 桥连热、光、电催化的表界面化学专栏 • 上一篇    下一篇

宽波段原位红外吸收光谱在Pd/SiO2和Cu/SiO2催化剂上CO氧化中的应用

翁雪霏,,, 杨双莉,, 丁丁, 陈明树(), 万惠霖   

  1. 厦门大学化学化工学院, 化学系, 固体表面物理化学国家重点实验室, 福建厦门361005
  • 收稿日期:2022-01-11 接受日期:2022-03-10 出版日期:2022-08-18 发布日期:2022-06-20
  • 通讯作者: 陈明树
  • 作者简介:第一联系人:

    共同第一作者.

    现工作单位: 中国科学院苏州纳米技术与纳米仿生研究所纳米真空互联实验站, 江苏苏州215123

  • 基金资助:
    国家自然科学基金(21872110);国家自然科学基金(21327901);国家自然科学基金(22102209);国家重点研发计划(2020YFB0606401)

Applications of in-situ wide spectral range infrared absorption spectroscopy for CO oxidation over Pd/SiO2 and Cu/SiO2 catalysts

Xuefei Weng,,, Shuangli Yang,, Ding Ding, Mingshu Chen(), Huilin Wan   

  1. State Key Laboratory of Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, China
  • Received:2022-01-11 Accepted:2022-03-10 Online:2022-08-18 Published:2022-06-20
  • Contact: Mingshu Chen
  • About author:First author contact:

    Contributed equally to this work.

    Current address: Vacuum Interconnected Nanotech Workstation, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, China

  • Supported by:
    National Natural Science Foundation of China(21872110);National Natural Science Foundation of China(21327901);National Natural Science Foundation of China(22102209);National Key Research and Development Plan of China(2020YFB0606401)

摘要:

多相催化的原位表征通常采用各种表征手段分别测试, 但由于不同表征方法原位池结构不同, 导致分别测试的温度、反应气氛及催化剂状态不尽相同, 特别是催化过程还存在温度、反应物和产物浓度梯度, 不同原位表征方法获取的信息可能来自不同的表面态, 此外一些表征方法还涉及到光子或电子等的影响, 难以获得实际催化过程准确全面的信息. 原位红外吸收光谱广泛应用于催化反应机理过程的动态表征, 然而多相催化体系中的氧化物组分通常对1200 cm‒1以下的红外光有较强的吸收, 且常规红外光源强度在低波数段迅速衰减, 目前原位红外光谱研究大多局限于4000‒900 cm‒1对催化剂表面吸附物种(包括反应中间体)的检测, 难以将其应用于反应过程中催化活性组分自身变化的研究, 如活性组分的氧化/还原、表面重构、活性组分与载体表面键合等, 这些信息多位于1200‒50 cm‒1. 基于模型催化剂表面厚度可控, 近年来作者应用镜面反射红外吸收光谱在几个体系的研究中均实现了在一张红外光谱中同时获取表面吸附物种、表面变化和反应产物生成等关键信息. 另一方面, 氧化硅是常用的多相催化剂载体, 其中硅溶胶易制成薄膜、稳定性好, 钯和铜作为催化剂活性组分广泛应用于实际多相催化反应过程, 且钯和铜的价态在催化反应中往往会发生动态变化, 确认真实活性相是一个难题.

本文通过自行研制的原位红外反应池及超薄样品制备方法, 在常规氧化物负载的实际多相催化剂体系获得了4000‒400 cm‒1范围内较高的红外光谱信号, 实现了反应条件下在一张红外光谱同时监测反应物、产物、表面吸附物种和催化剂自身的变化. 以商业上常用的Pd/SiO2和Cu/SiO2催化剂上CO氧化反应为例, 利用宽波段原位红外光谱观察到Pd2+‒O (670, 608 cm-1), Cu+‒O (635 cm-1)和Cu2+‒O (595, 535 cm-1)等氧化物的特征峰, 并原位跟踪了CO氧化反应过程中Pd和Cu活性组分氧化/还原态的动态变化, 进一步结合准原位X射线光电子能谱测试结果相互佐证, 证实了钯和铜的氧化/还原. 实验结果表明, Pd/SiO2和Cu/SiO2催化剂在CO氧化反应条件下, 其活性组分分别以Pd0和Cu+稳定存在.综上, 本文方法可以提供更为可信的催化剂结构和催化性能相关信息, 为多相催化的原位表征提供了新机遇.

关键词: 原位红外光谱, X射线光电子能谱, 多相催化, CO氧化, 钯,

Abstract:

Infrared (IR) absorption spectroscopy has been widely used for dynamic characterization of catalysts and mechanism of catalytic reactions. However, due to the strong infrared absorption of heterogeneous catalysts (mainly oxides, or supported metal and metal oxides, etc.) below 1200 cm-1, and the intensity of regular infrared light source rapidly decays at low-wavenumber range, most in-situ infrared spectroscopy studies are limited to the detection of surface adsorbates in the range of 4000-900 cm-1. The change of catalytically active component itself (M-O, M-M bond, etc., 1200-50 cm-1) during the reaction is hard to be tracked under reaction conditions by in-situ IR. In this work, a home-made in-situ IR reactor was designed and a sample preparing method was developed. With such progresses, the changes of reactants, products, surface adsorbates, and catalysts themselves can be measured under the same reaction conditions with a spectral range of 4000-400 cm-1, providing a new opportunity for in-situ characterization of heterogeneous catalysis. CO oxidation on Pd/SiO2 and Cu/SiO2 catalysts were taken as examples, since both the two catalytic systems were extensively used commercially, and moreover reduction and oxidation of palladium and copper occur during the examined reaction conditions. The characteristic bands of Pd2+-O (670, 608 cm-1), Cu+-O (635 cm-1) and Cu2+-O (595, 535 cm-1) were observed by IR, and the changes during CO oxidation reaction were successfully monitored by IR. The oxidation/reduction of palladium and copper were also confirmed by ex-situ XPS. Moreover, Pd0 in Pd/SiO2 and Cu+ in Cu/SiO2 were found as the thermal dynamically stable phases under the examined conditions for CO oxidation.

Key words: In-situ infrared spectroscopy, X-ray photoelectron spectroscopy, Heterogeneous catalysis, CO oxidation, Palladium, Copper