(739b) In Situ XAFS Analysis of Precious Metal Catalysts during Ethanol Steam Reforming

Renewable sources of liquid fuels have recently received much attention for their promising ability to reduce our dependence on fossil fuels. Biological sources are capable of producing these energy sources, however the oxygen inherent to the chemical makeup of the fuel is detrimental to the fuel’s energy density. Hydrodeoxygenation (HDO) of biofuels is one of the more effective means of removing the oxygen functional groups, but this process requires an external source of gaseous hydrogen. Here we explore the steam reforming of the oxygenated fuels themselves to produce this hydrogen. The steam reforming of ethanol over bimetallic rhodium (Rh) and platinum (Pt) catalysts has been used as a test case. Catalyst deactivation is one of the major challenges faced in fuel reforming and there exists a need to determine the primary causes. In order to determine the underlying origins of catalyst deactivation, in situ X-ray absorption fine structure (XAFS) measurements were taken to monitor any conformational and oxidation state changes to the precious metals of the catalyst during steam reforming. The Rh K-edge and Pt L₃-edge were examined to determine how the changing natures of each metal contribute to the overall behavior of the system. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra were collected at each stage of ethanol reforming including regeneration. It was found that the product distribution and selectivity toward hydrogen was strongly dependent on the oxidation state and conformation of Rh. It is expected that further characterization through these techniques will provide a more thorough understanding of catalyst deactivation in general thereby allowing for catalyst development that is more targeted with regards to activity and robustness.