宽波段原位透射红外光谱在多相催化研究的应用

Fundamental understanding of catalysts and how they function under the reaction conditions is the foundation for design and preparation of new and improved catalysts and catalytic conversion processes. Such understanding can be achieved only by characterization of catalysts in the presence of reacting mixtures at the temperatures and pressures of practical operation because catalyst structures and the mechanisms of catalytic reactions depend on the reaction environment. Raman spectroscopy is one of the few instrumental methods that in a single measurement can provide information about both solid catalysts and the molecules reacting on them. However, its sensitivity for the submonolayer surface species and the surface change under catalytic reaction is limited. Infrared spectroscopy is also a wide spectral range (6000-50 cm-1) technique that enables examination of the nature of molecular species, identification of solid phases. Unfortunately, most of the heterogeneous catalysts consist of oxides as the active components or as the supports, which strong IR adsorption (below 1200 cm-1) limits the in situ IR to measure only the surface species (4000~900 cm-1). Chen et al. had successfully developed in-situ mid- and far- IR characterization methods, that extends the spectral range in current in-situ catalytic characterization from 4000~900 cm-1 to 4000~450 cm-1. Such improvements make the in-situ IR become one of the few in-situ characterization methods that in a single measurement can provide information about both solid catalysts and the molecules reacting on them. In the present project, a new in-situ reaction cell will be designed to fulfil the requirements of a stable background and achieving a low temperature under a realistic catalytic reaction condition. Methods to prepare various oxide support thin films of SiO2, Al2O3, TiO2, MgO, etc. will be developed. Such thin films can be served as supports for catalyst active components that with high infrared transmittance. In-situ infrared study samples for various catalyst systems will be prepared with high infrared transmittance, and detail in-situ characterization under catalytic reaction conditions will be conducted. Detail correlation between the surface changes, the active surface species, as well as the catalytic performance can be established. Such one measurement to obtain information of both the surface species and the change of the surface itself should be a powerful technique for in-situ characterization of catalysts and reaction mechanisms.

多相催化反应是非常复杂的表界面过程，对其深入认识依赖于实际催化反应条件下的原位表征技术取得突破性进展以获取关键的催化剂表面结构和表面物种信息。申请人前期发展的宽波段原位红外光谱技术（4000~400 cm-1）可以在实际反应气氛中原位检测催化反应过程中的表面物种（反应中间体），而且能同时跟踪催化剂自身的表面变化，为催化剂作用机理和催化反应机理的准确认知提供重要机遇。本项目拟在已有工作基础上，完善宽波段原位透射红外光谱池，研制不同常规多相催化剂载体的高红外光透过薄膜，制备与实际催化剂相近乃至实际催化剂的高红外光透过样品膜，拓广宽波段原位透射红外光谱研究技术，为多相催化的原位表征提供新机遇。基于宽波段原位透射红外光谱在同时检测催化剂表面吸附物种和催化剂自身变化的优势，详细研究几个典型催化剂体系，以期更深入理解相关催化反应的催化剂作用机理和催化反应机理。

多相催化反应过程是复杂的表界面过程，限于表征技术、对其认识还不够深入，往往被称为‘黑箱’，在分子、原子水平理解催化过程将取决于实际催化反应条件下的原位表征技术取得突破性进展以获取关键的催化剂表面结构和表面物种信息。本项目着重发展宽波段原位红外光谱技术（4000~450 cm-1）可以在实际反应气氛中原位检测催化反应过程中的表面物种（反应中间体），而且能同时跟踪催化剂自身的表面变化，以能为催化剂作用机理和催化反应机理的准确认知提供重要机遇。项目研究在已有工作基础上，逐渐完善宽波段原位透射红外光谱池，从氧化物溶胶研制了SiO2, Al2O3, TiO2等常规多相催化剂载体的高红外光透过薄膜，再将催化剂活性组分（Pd, Rh, Cu等）分散于所制备薄膜上制成与实际催化剂相近乃至实际催化剂的高红外光透过样品膜；并结合结构明确的模型表面（Pd(111), Pt(111), Cu(111)等单晶面及其上生长的结构规整氧化物膜）应用自行搭建的宽波段镜面反射红外吸收光谱，详细研究了几个体系的氧化还原、及在CO催化氧化/加氢过程表面吸附物种的变化和表面变化；尝试研究了几个实际催化剂体系（ZnCrO- Al2O3, Pd/ SiO2, Rh/ SiO2, Pd/ Al2O3, Rh/ Al2O3, Cu/ Al2O3, Cu/ SiO2, Pd/ TiO2, Cu/ CeO2,…）。发现以氧化物溶胶制备的原位催化剂样品和模型表面，宽波段原位红外光谱可以在一张谱图中同时获得表面吸附物种和催化剂表面变化信息，较好获悉催化剂的活性表面、活性催化中心本质；实际催化剂体系在低波数仍只有较低的透过性、且表面变化复杂，有待进一步完善制样技术。项目研究拓广宽波段原位透射红外光谱研究技术，实现原位透射/反射红外光谱同时检测催化剂表面吸附物种和催化剂自身变化，为更深入理解相关催化反应的催化剂作用机理和催化反应机理提供新机遇。