纳米片状Mn基尖晶石催化剂氧空穴调控及其VOCs氧化原位质谱、调制激发红外光谱研究

Aiming at the problem of the low activity on spinel type catalysts for VOCs oxidation, the unclear structure-activity relationship and oxygen species circulation, and the incomplete information about adsorbed active species on surface and the real reaction mechanism, nanosheet AMn2O4 spinel catalysts (A: Co, Cu) with high surface area and different oxygen vacancies distribution will be constructed in this project, which shows the properties of easy metal doping, good ability of mass exchange and gas diffusion. VOCs oxidation activity will be strongly enhanced due to the multivalent properties of different elements, high activity of oxygen species in AMn2O4 spinel catalysts and the evolution of oxygen vacancy. Herein we will pay more attention on the formation mechanism of oxygen vacancies on Mn-based spinel catalyst, and constructing the fundamental knowledge of interrelation of oxygen vacancies with the catalyst structure, oxygen species circulation and VOCs catalytic oxidation performance. In addition, dynamic surface processes and reaction mechanisms under reaction conditions will be investigated by in situ diffuse reflectance Fourier transform IR spectroscopy (DRIFTS) combining with the modulation excitation spectroscopic (MES) technique to bridge a gap between material science and VOC oxidation. A particular emphasis is placed on concentration-modulation experiments to gain detailed insight into adsorption-desorption dynamics of VOCs gaseous component, discrimination between active and spectator species, identification/quantification of intermediates directly involved in the VOC oxidation cycles, providing a reliable basis for optimizing the efficiency of the catalysts. The innovative breakthroughs in the VOC removal on spinel type catalysts and a deep understanding of the activity and selectivity difference between spinel catalyst and other oxides will be made in the aid of the state-of-the-art spectroscopic technique, i.e., MES, and DFT. The obtained results will show significant effects on understanding of the effect of oxygen vacancies, the transfer pathway of oxygen species of spinel catalysts in VOCs oxidation, and the underlying mechanisms of VOC oxidation at the molecular level. These will eventually light up a path for development of the novel environmentally friendly catalysts for VOCs removal industry.

本项目针对尖晶石类催化剂对VOCs氧化活性相对较低，构效关系、氧物种循环和反应物表面吸附信息不完整、反应机制不清晰等问题，制备具有大比表面积、易于元素掺杂、质量交换和气体扩散的纳米片状具有不同氧空穴分布的AMn2O4尖晶石催化剂(A: Co, Cu)，利用元素多价态、较好氧活性及氧空穴调控等提高VOCs氧化活性；系统研究尖晶石催化剂中氧空穴形成机制，对催化剂结构、氧物种循环及VOCs催化氧化性能的作用；利用调制激发与相敏检测原位红外技术，实时监测在实际工作条件下气固界面瞬态表面吸附物种，深刻理解尖晶石催化剂与其他复合氧化物反应初期活性和选择性差异，并结合密度泛函理论(DFT)计算，较全面获得VOCs在尖晶石催化剂上吸附、活化、中间物种生成及消耗、氧物种循环和反应机制，对进一步理解VOCs氧化中催化剂氧空穴作用、氧循环过程，建立分子水平上反应机制，实现构筑高效且环境友好催化剂系具有重要意义。

本项目以Mn基尖晶石催化剂为研究体系，通过晶相结构、酸刻蚀以及外源掺杂（稀土金属、贵金属）等调控手段，构建了不同氧空位浓度的CoMn2O4尖晶石催化剂进而优化VOCs催化氧化性能；系统考察了催化剂氧空位含量与催化反应性能之间的关系；重点研究了甲苯反应过程中氧物种的消耗和补充过程，加深了对Mn基尖晶石催化剂上甲苯催化氧化反应机理的认知。溶胶凝胶法制备的CoMn2O4尖晶石催化剂相较于负载型Mn氧化物，有着丰富的氧空位、较大的比表面积以及较高流动性能的氧物种，显著加速了甲苯催化氧化反应；采用酸刻蚀策略构建出不同氧空位浓度的CoMn2O4尖晶石催化剂，由于阳离子空位和晶格畸变的存在，形成了丰富的氧空位促进了甲苯快速氧化；原位溶剂热诱导镧掺杂到CoMn2O4尖晶石晶格调控氧物种活性来提高甲苯、甲醛、丙酮和乙酸乙酯催化氧化性能；利用丰富氧空位对Pt的锚定作用，采用液相原位法构建Pt掺杂的CoMn2O4催化剂，增强甲苯与催化剂之间的相互作用使甲苯在180 °C完全转化。结合原位质谱-红外与DFT计算，氧空位存在增强了晶格氧流动性，探究并构建了氧物种在催化剂上的“消耗-迁移-转化”模型，甲苯氧化通过苯甲醇-苯甲酸盐-酸酐-乙酸盐的反应路径进行，酸酐的氧化这一反应速控步骤在富含氧空位的尖晶石催化剂上显著加快，从而提高催化剂的低温甲苯催化活性。