In Situ Spectroscopic Analysis of Active Structures of Catalysts

Over the past 25 years, the in situ X ray absorption fine structure (XAFS) technique aiming for observation of catalysts under various reaction conditions has been developed and improved. The importance of in situ analysis was confirmed by observation of the rhodium (Rh) species of carbon dioxide hydrogenation catalysts. In situ XAFS identified 1.3 nm Rh clusters, different from the structure observed in the quenched catalyst. Simultaneous measurement of in situ XAFS and Fourier transform infrared spectroscopy (FTIR) provided information on both the active structure and reaction intermediates. In situ XAFS and FTIR observation of nickel phosphide catalysts during hydrodesulfurization of thiophen revealed that the nickel phosphosulfide species was the active structure. A novel reaction which produces hydrogen cyanide (HCN) from methane and nitric oxide at around 400 °C over supported platinum (Pt) catalysts was found. In situ FTIR confirmed the presence of Pt with a cyano ligand (Pt–CN). In situ X ray absorption near edge structure (XANES) showed changes corresponding to Pt–CN species. Pt–CN was proved to be the precursor of HCN, but also acted as an inhibitor of the reaction. Comprehensive understanding of reaction mechanisms of catalytic reactions requires methods for simultaneous observation of catalysts and reactants. Application of multiprobe analysis to catalytic reactions is much anticipated.