In Situ Soft X-ray Absorption Spectroscopy Applied to Solid-Liquid Heterogeneous Cyanopyrazine Hydration Reaction on Titanium Oxide Catalyst

In conventional in situ spectroscopies of solid-liquid heterogeneous catalytic reactions, it is difficult to measure the conversion of liquid substrates on solid catalysts due to the lack of sensitivity and the difficulty in separation of target signals in the mixture of substrates, reactants, products, solvents, and solid catalysts. Element-specific soft X-ray absorption spectroscopy (XAS) is a promising method to detect target substrate and product separately from the other components using chemically different inner shell excitation energies. In the present work, we have developed an in situ sample cell to measure time- and temperature-dependent XAS spectra in transmission mode and applied it to one of the solid-liquid heterogeneous catalytic reactions, cyanopyrazine (PzCN) hydration to produce pyrazinamide (PzCONH(2)) on the TiO2 catalyst (PzCN + H2O -> PzCONH(2)). We have succeeded in unambiguous observation of the spectral change in the C K-edge and N K-edge XAS due to the production of PzCONH(2) from PzCN during the reaction regardless of the coexistence of the bulk liquid components, H2O (reactant) and EtOH (solvent). Furthermore, we have obtained reasonable kinetic properties in the PzCN hydration reaction from the spectral analysis such as the reaction order (first order), the rate constant, and the activation energy. Thus, the present method can be widely applicable to distinguish the minor liquid components in chemical reactions.