Using fractional desorption spectroscopy to determine kinetic parameters for surface processes

Fractional desorption spectroscopy (FDS) is an interesting new approach for the determination of activation energies for a large range of surface proc esses. The activation energy can be determined over a wide coverage range u sing a single experiment. The FDS method utilizes a modulated temperature p rogram during the desorption experiment by applying a modified Arrhenius an alysis to extract kinetic parameters from desorption rate vs temperature da ta. FDS improves on other differential approaches in two important aspects. First, it enables determination of the activation energy over a range of a ccessible surface concentrations in a single adsorption/desorption experime nt. This is particularly useful for studying surface reactions involving mu ltiple species or in cases where complex surface preparations an required p rior to the temperature-programmed desorption (TPD) experiment. Second, the FDS method possesses unique self-diagnostic and system-diagnostic abilitie s. The self-diagnostic aspect of the method enables a more systematic appro ach to eliminating errors from baseline drift. Like other differential appr oaches, the FDS method does not require assumptions about the reaction orde r, frequency factor, or the dependence of activation energy on surface conc entrations. In this paper, the FDS method is shown effective in estimating concentration-dependent activation energies for first-order desorption, sec ond-order desorption, and binary surface reaction processes, using straight forward desorption models. We experimentally validate the FDS method by app lying the technique to determine the activation energy for CO desorption, O atom recombination and desorption, and CO2 formation from adsorbed CO and O atoms, all on the Pt(lll) surface. The FDS-determined activation energies for these systems are in excellent agreement with values established in th e literature.