Since the first report which shed light on new functions of metal phosphide materials as hydrodesulfurization (HDS) catalysts by Oyama, a lot of effort has been made to develop catalysts which excel the current industrial catalysts.   Among various metal phosphides, Ni2P showed the highest performance.   Analysis by X-ray diffraction and extended X-ray absorption fine structure (EXAFS) showed that the bulk Ni2P structure was retained under HDS reaction conditions, but it also suggested the presence of sulfur on Ni2P, which seemed to work as a promoter rather than a poison.  In order to reveal the role of sulfur species and determine the active structure, a time-resolved combined in situ XAFS and Fourier transform infrared (FTIR) technique was developed and applied to supported Ni2P catalysts under thiophene HDS conditions together with product analysis by mass spectroscopy (QMS).   The experiment was conducted at Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization, in Japan.  Under the thiophene HDS conditions at 513 K, adsorbed tetrahydrothiophene (THT) was observed by FTIR, following the formation of a nickel phosphosulfide phase (NiPS) indicated by Ni K-edge Quick XAFS.  Detection of the HDS products by QMS coincided with the THT formation.  These results suggested that during the induction period NiPS was formed on the Ni2P surface, then the catalytic HDS reaction proceeded on NiPS.   In other words, it is shown that NiPS worked as the active phase and THT was identified as a reaction intermediate for the HDS reaction.  Combined in situ analysis enables us to see catalysts with different methods simultaneously, and allows us to connect the obtained data with high precision.  This technique proved to be a powerful tool for the precise study of reaction intermediates and the catalytic reaction path.

Combined in situ XAFS and FTIR study of Ni phosphide catalysts

248th National Meeting (2014)

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