Decomposition of formic acid on Ni(110): I. Flash decomposition from the clean surface and flash desorption of reaction products

Abstract

The flash decomposition of adsorbed formic acid on clean Ni〈110〉 produced H 2O, CO, H 2, and CO 2 peaks. The CO decomposition peak appeared at much higher temperatures than the H 2 or CO 2 decomposition peaks; it was identical to the flash desorption peak of adsorbed CO. The H 2O peak was observed at temperatures well below the H 2 and CO 2 decomposition peaks. The H 2 and CO 2 decomposition peaks were identical and quite narrow. The insensitivity of the peak temperature of H 2 and CO 2 to initial coverage and the detailed peak shapes were inexplicable by simple mechanisms; they were suggestive of an autocatalytic decomposition. The hydrogen decomposition peak occurred at a much higher temperature than the flash desorption peak of H 2. The initial sticking probability of formic acid was near unity at room temperature. Low exposures to formic acid produced CO and surface oxidation. The sticking probability of H 2 was quite temperature sensitive, increasing from 0.01 to 0.5 between 50 and −25 °C; it was immeasurable on a carbon-covered surface. The initial sticking probability of CO was 0.7 ± 0.2. Decomposition of CO 2 to adsorbed CO and O occurred with a probability of 0.15 per incident CO 2 molecule.