Flash desorption activation energies: DCOOH decomposition and CO desorption from Ni (110)

Abstract

Accurate values of activation energies were measured by flash desorption methods without assumptions about preexponential factors, reaction orders or specific reaction mechanisms. The activation energies were determined by two methods; one method employed a relationship for the shift in peak temperature with change in heating rate, and the other utilized the change in peak amplitude with shift in peak temperature for different heating rates. Agreement between the two methods was excellent. A series of flash curves at different heating rates were obtained for the CO 2 and CO products from DCOOH flash decomposition following adsorption on Ni (110) at 37°C. Adsorbed DCOOH decomposed autocatalytically with an activation energy of 26.6 kcal/mol to form CO 2 and D 2. Carbon monoxide formation from DCOOH decomposition, which corresponded identically to CO desorption from this surface, showed a first order activation energy of 32.7 kcal/mol; this activation energy was used to fit a series of CO flash desorption curves obtained for CO adsorption at −55°C. The preexponential factor was found to be 8.5 × 10 15 s −1. The desorption was first order with a slightly coverage dependent desorption energy. In addition the CO flash curves showed additional binding states at coverages at which changes in isosteric heats of adsorption have been observed. The results illustrate the sensitivity of flash desorption for the determination of binding energies over a wide range of coverages.