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

点击翻译按钮获取中文摘要

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.