Gas-solid photocatalytic oxidation of dinitrogen to nitrogen oxides: Mechanism and kinetics

该项目的目的是详细了解在气固反应中将氮气光催化氧化为氮氧化物的过程。最近发现的这一耐人寻味的反应可能使硝酸盐的可持续合成成为一种全新的方法，例如用作(太阳能)肥料。在气相中进行反应的显著优点是可以精确地控制水氮比，抑制作为副反应的不必要的水氧化和还原。然而，目前对这种反应的了解很少，所以这个项目将为详细的机理和动力学理解奠定基础。因此，这一具有挑战性的目标需要来自光谱学、催化和反应工程的互补专业知识。为此，第一个目标是通过识别所有反应伙伴和产物，包括相应还原反应的反应伙伴和产物，来完全关闭反应的物质平衡。这将使我们能够适当地建立分析方法，并开发用于光催化剂材料常规评估的筛选方案。由于目前缺乏对氮氧化的系统研究，通过系统地将金属离子(V、Mo、W、Fe、Pd、铂、铜)和低聚物接枝到TiO2光催化剂上，并对其光催化活性进行评价，将寻找合适的氮氧化共催化剂。金属的选择是基于在氮氧化或作为逆反应的NO的分解中被证明的催化活性。由于二氧化钛对该反应具有良好的光催化活性和合适的光电性质，因此将被使用。核心目标是揭示该反应的机理和动力学与所采用的反应条件(例如，温度、气相组成和光强度)的关系。利用原位和时间分辨激光光谱学，可以研究半导体内部的载流子动力学以及它们与催化点的相互作用。利用拉曼光谱和红外光谱对催化剂的表面进行了表征，并对催化剂的中间物种和吸附行为进行了表征。这些信息将与反应速率和形成的产物的数据联系起来，以获得一个整体的机理和动力学模型，作为未来研究的基础。

The aim of the project is to attain a detailed understanding of the photocatalytic oxidation of N2 to nitrogen oxides in a gas-solid reaction. This recently discovered intriguing reaction could enable a completely new way for the sustainable synthesis of nitrates to be used for instance as (solar) fertilizers. Conducting the reaction in the gas phase has the significant advantage that the water-to-nitrogen ratio can be precisely controlled, suppressing the unwanted water oxidation and reduction as side-reactions. However, there is currently little knowledge of this reaction so this project will lay the foundation of a detailed mechanistic and kinetic understanding. This challenging goal thus requires complementary expertise from spectroscopy, catalysis, and reaction engineering working in concert.The first objective towards this end is to fully close the reaction’s material balance by identifying all reaction partners and products, including those of the corresponding reduction reaction. This will enable us to properly set up analytics and develop a screening protocol for routine evaluation of photocatalyst materials. As a systematic study on the topic is currently missing, suitable co-catalysts for nitrogen oxidation will be identified by systematically grafting metal ions (V, Mo, W, Fe, Pd, Pt, Cu) and oligomers onto TiO2, and evaluation of their photocatalytic activity. The metals are chosen based on proven catalytic activity in either the nitrogen oxidation or the decomposition of NO as the reverse reaction. TiO2 will be used as it has proven photocatalytic activity for this reaction and thereby suitable optoelectronic properties.The core objective is to unravel both, the mechanism, and the kinetics of the reaction in dependence of the employed reaction conditions (e.g., temperature, gas phase composition, and light intensity) . Using in situ and time-resolved laser spectroscopy, both the charge-carrier dynamics inside the semiconductor and their interaction with the catalytic sites will be interrogated. Raman and infrared spectroscopy are used to probe the surface of the catalyst and identify intermediate species and adsorption behavior. This information will be linked with data on the reaction rate and formed products to obtain a holistic mechanistic and kinetic model as foundation for future studies.