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Binding Energy and Diffusion Barrier of Formic Acid on Pd(111)
Jan Fingerhut1, Loïc Lecroart2, Dmitriy Borodin1,2
1Institute for Physical Chemistry, Georg-August University of Goettingen, Goettingen 37077, Germany.
Abstract:
Velocity-resolved kinetics is used to measure the thermal rate of formic acid desorption from Pd(111) between 228 and 273 K for four isotopologues: HCOOH, HCOOD, DCOOH, DCOOD. Upon molecular adsorption, formic acid undergoes decomposition to CO2 and H2 and thermal desorption. To disentangle the contributions of individual processes, we implement a mass-balance-based calibration procedure from which the branching ratio between desorption and decomposition for formic acid is determined. From experimentally derived elementary desorption rate constants, we obtain the binding energy 639 ± 8 meV and the diffusion barrier 370 ± 130 meV using the detailed balance rate model (DBRM). The DBRM explains the observed kinetic isotope effects.
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