A vibrational study of formic acid interaction with clean and oxygen-covered silver (110) surfaces

Abstract

The interaction of formic acid (HCOOH) with clean and atomic oxygen-covered Ag(110) surfaces has been investigated with electron energy loss spectroscopy (EELS) and temperature programmed reaction spectroscopy (TPRS). The correlation between product desorption from the surface and the presence of surface intermediates has been investigated. On the clean Ag(110) surface, formic acid adsorbed and desorbed in molecular form and no dissociation was noted. The interaction energy was estimated to be 11 kcal mole −1. Atomic oxygen was generated on the Ag(110) surface by dissociation of adsorbed di-oxygen. This di-oxygen complex was a precursor to the atomic state. Formic acid interacted with the atomic oxygen at 100 K producing adsorbed water and formate (HCOO). Annealing this surface resulted in water desorption near 200 K, and the formate decomposed to CO 2 and H 2 near 400 K. Verification of formate (HCOO) was made by substituting the deuterated acid to generate DCOO species. The spectral assignments agreed with the formate ion in solution. We were also able to assign the in-and-out-of-plane bending modes associated with motion of the hydrogen and deuterium atoms. Due to screening of the asymmetric stretch (ν a(COO)) of the formate groups in a symmetrical bidentate bonding configuration at the surface, we were able to observe changes in the formate orientations with temperature prior to decomposition. Excellent agreement was found between the frequencies reported in this work and recent Raman data for HCOO −adsorbed on silver particles.