Application of SIMS-FDS-AES combined system to surface studies—adsorption and decomposition of formic acid over clean surface of nickel

Abstract

The catalytic decomposition of formic acid was studied by a combined system of SIMS (secondary ion mass spectroscopy) - FDS (flash desorption spectroscopy) - AES (Auger electron spectroscopy). Deuterium labeled formic acids (HCOOH, DCOOH and HCOOD) were used to elucidate the reaction mechanism. SIMS measurements revealed that the adsorption layer after exposure of DCOOH at room temperature mainly consisted of D, O, OD, DCO and DCOO. As the temperature of sample was elevated linearly, DCO + and D + ion signals disappeared completely from the surface at 380 K and 450 K, respectively. The activation energy of DCO(a) dissociation into D(a) and CO(a) was estimated to be 7.7 kcal/mol from the variation of surface concentration. FDS showed that the decomposition products were D 2, CO 2 and CO. D 2 and CO 2 had a peak at 360 K, CO at 410 K. The activation energies for desorption corresponding to these peaks were estimated to be 20–22 kcal/mol for D 2 and CO 2, and 29.5 kcal/mol for CO. The reaction mechanism was proposed based upon the results obtained from the SIMS- FDS-AES combined system. The usefulness of this system to heterogeneous catalysis was demonstrated.