NMR Spectroscopic Evidence for an Intermediate of Formic Acid in the Water−Gas−Shift Reaction

The water−gas−shift (WGS) reaction (CO + H 2 O ⇄ CO 2 + H 2 ) is investigated in connection to formic acid. Using NMR spectroscopy, the reversible decomposition pathways of formic acid to both sides of the WGS reaction are studied in hot water at 240−260 °C. This reversibility strongly suggests that formic acid exists as an intermediate in the WGS reaction, and it is indeed demonstrated that carbon monoxide is treated in hot water to produce formic acid. The present result enables us to generate and store hydrogen in the liquid form of formic acid and to transform formic acid to hydrogen in water by tuning the thermodynamic conditions.