Transition metal phosphides as stable and highly selective catalysts for the dehydrogenation of aliphatic and cyclic alkanes

可再生氢的利用和生产在未来基础化学品和能源载体的生产中发挥着重要作用。这就要求加氢和脱氢反应需要坚固的、选择性的多相催化剂。通过在过渡金属催化剂中掺入引入电子和位阻效应的非金属元素，可以提高过渡金属催化剂的抗性和选择性。磷已成为一种特别有效的掺杂元素来修饰多相催化剂。例如，贵金属与磷的掺杂和晶体过渡金属磷化物（TMPs）的形成在各种加氢和脱氢反应中显示出积极的活性、选择性和稳定性。在我们自己的初步工作中，我们特别证明了TMPs对烧结和焦化的显著抗性，以及与不含磷的对应物相比脱氢活性的增加。该项目的重点是铂基和钼基TMP催化剂的开发和研究，用于线性和环碳氢化合物的脱氢。本项目第一部分（AP 1）将开发和研究以磷盐为前驱体合成TMP技术催化剂的新方法。通过与最先进的合成方法进行比较，该项目旨在阐明磷路线是否会产生具有更高活性表面和更好性能的催化剂。在项目（AP 2）的进一步过程中，将研究过渡金属催化剂的磷改性是否可以增加对常见失活机制（烧结，焦化）的抗性，以及在失活情况下如何再生材料。为此，不同成分的TMP催化剂将在吸附分析仪（XEMIS）中暴露于热应力循环中，并自动分析焦炭形成和表面变化。随后，将选择具有高活性表面积的强效催化剂进行进一步研究。在最后的项目部分（AP 3）中，将研究制备并表征的Mo-和pt基TMP催化剂在环甲基环己烷和线性正庚烷气相脱氢中的催化性能。两种底物的碳数（C7）相同，可以很好地比较TMPs对线性烷烃和环烷烃脱氢的催化性能。本项目的目标不仅是了解磷改性对催化剂稳定性的影响，而且探索其对挑战性脱氢反应的活性和选择性的积极影响。

The use and production of renewable hydrogen plays an important role in the future production of base chemicals and energy carriers. This requires robust and selective heterogeneous catalysts for hydrogenation and dehydrogenation reactions. By doping with non-metallic elements, that introduce electronic and steric effects, the resistance and selectivity of transition metal catalysts can be increased. Phosphorus has emerged as a particularly effective doping element for modifying heterogeneous catalysts. For example, doping of noble metals with phosphorus and the formation of crystalline transition metal phosphides (TMPs) has shown positive effects on activity, selectivity, and stability in various hydrogenation and dehydrogenation reactions. In our own preliminary work, we particularly demonstrated a remarkable resistance of TMPs against sintering and coking and an increase in dehydrogenation activity, compared to phosphorus-free counterparts. The project focuses on the development and investigation of platinum and molybdenum-based TMP catalysts for the dehydrogenation of linear and cyclic hydrocarbons. In the first part of the project (AP 1), a new synthesis method for technical TMP catalysts using phosphonium salts as a phosphorus precursor will be developed and investigated. By comparing to state-of-the-art synthesis methods, the project aims to clarify whether the phosphonium route leads to catalysts with higher active surface and better performance. In the further course of the project (AP 2), it will be investigated whether the phosphorus modification of transition metal catalysts can increase resistance to common deactivation mechanisms (sintering, coking) and how the materials can be regenerated in case of deactivation. For this purpose, TMP catalysts of different compositions will be exposed to thermal stress cycles in a sorption analyzer (XEMIS) and automatically analyzed for coke formation and surface changes. Subsequently, robust catalysts with high active surface area will be selected for further studies. In the final project part (AP 3), the catalytic properties of the prepared and characterized Mo- and Pt-based TMP catalysts will be investigated in the gas phase dehydrogenation of cyclic methylcyclohexane and linear n-heptane. The identical carbon number (C7) of both example substrates allows for a good comparison of catalytic properties of TMPs for the dehydrogenation of linear and cyclic alkanes. The goal of this project is not only to understand the influence on catalyst stability through the phosphorus modification, but also to explore its positive effects on activity and selectivity in challenging dehydrogenation reactions.