Adsorption and Decomposition of Formic Acid on Cobalt (0001)

Formic acid can undergo dehydration or dehydrogenation with variable selectivity over a range of metal catalysts. The selectivity among these reactions depends on the reaction mechanism and reaction conditions pertinent on each surface. This work provides mechanistic insight into the decomposition of formic acid on cobalt at high- and low-temperature regimes. The adsorption and decomposition of formic acid on a Co(0001) single crystal was studied in ultrahigh vacuum by X-ray photoelectron spectroscopy and temperature-programmed desorption. Insight is provided using density functional theory calculations. In the low-temperature regime, formic acid adsorbs molecularly on the surface at 130 K. Partial decomposition produces CO at 140 K, and at 160 K, the decomposition of formic acid into formate, which is a thermodynamic sink, is dominant. Water can be formed at low temperature via bimolecular processes. At high temperature (>400 K), the similar barriers for decomposition of the formate species lead to the concomitant production of CO, CO2, and H-2. The correlation between experiment and theory provides a framework for the interpretation of surface species and reaction path operating in different regimes.