Binding Energy and Diffusion Barrier of Formic Acid on Pd(111)

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 H-2 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 & PLUSMN; 8 meV and the diffusion barrier 370 & PLUSMN; 130 meV using the detailed balance rate model (DBRM). The DBRM explains the observed kinetic isotope effects.

Automated summary

Velocity-resolved kinetics was used to measure the thermal rate of formic acid desorption from Pd(111) surface for four isotopologues. A mass-balance-based calibration procedure was implemented to determine the branching ratio between desorption and decomposition for formic acid. The detailed balance rate model (DBRM) was used to obtain the binding energy and diffusion barrier from experimentally derived desorption rate constants, and it explained the observed kinetic isotope effects.