Single Site Catalysis for Direct Conversion of Methane to Ethylene and Aromatics: Design, Test and Operando Characterization

点击翻译按钮获取中文摘要

Light olefins and aromatics like ethylene, propylene and benzene are important building blocks for a wide range of chemical commodities such as cosmetics, lubricants, detergents and polymers. The direct and thus energy and cost-saving conversion of methane to these chemicals remains one of the grand challenges for chemistry because the methane molecule is very stable and difficult to activate. A Fe©SiO2 catalyst with iron single sites embedded within a silica matrix has recently been found to enable direct conversion of methane to ethylene and aromatics with extraordinary efficiency. The goal of this project is to identify the structure and composition of the active sites of the Fe©SiO2 catalyst and the reaction mechanism of direct methane conversion in order to gain comprehensive insight into the nature of this novel type of catalyst. This will allow its further rational improvement and potentially lead to even better catalysts for production of specific olefins and aromatics. For this purpose, single site metal catalysts will be prepared via different preparation methods including advanced routes such as flame spray pyrolysis. The latter is a versatile method for one step synthesis of nano-sized crystalline materials. Apart from iron, single site catalysts based on other metals (e.g. Mo) will be explored. On the one hand such alternative single site catalysts may exhibit even higher activity for direct conversion of methane or enable better tuning of the product selectivity. On the other hand, the investigation of different single site metal catalysts will lead to a better fundamental understanding of the structural requirements for methane activation, paving the way for optimizing both methane conversion and product selectivity towards specific olefins and aromatics.To reach this target, catalysts will be thoroughly characterized using complementary techniques including scanning transmission electron microscopy (STEM), Raman and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and extended X-ray absorption fine structure (EXAFS). The catalytic activity will be investigated in detail including reaction kinetic and deactivation studies. Promising catalyst systems will be studied in situ using advanced synchrotron X-ray based methods such as high energy-resolution fluorescence detected X-ray absorption near edge spectroscopy (HERFD-XANES) and X-ray emission spectroscopy (XES). Finally, operando X-ray based studies will be used to monitor the structure of selected catalysts under reaction conditions up to1250 K.We anticipate that a detailed picture will emerge of both the structure of single site metal catalysts and their role in methane activation from the results of these in situ and operando spectroscopic analysis methods. Moreover, the combination with reaction kinetic analyses will lead to a better mechanistic understanding of methane conversion into olefins and aromatics over supported single site metal catalysts.