Influence of Coverage Dependence on the Thermophysical Properties of Adsorbates and Its Impact on Microkinetic Models.

Abstract

This work focuses on the impact of lateral interactions on the thermophysical properties of adsorbates. We present different parametrizations for coverage-dependent enthalpy, entropy, and heat capacity in a mean-field microkinetic model. These models are tested against two systems, CO/Pt(111) and CO/Co(0001), using two different functionals. A detailed investigation into how coverage influences the thermophysical properties of CO* is presented. We place particular emphasis on studying the impact of coverage on the vibrational partition function and how this affects the entropy of adsorbates. Higher coverages typically lead to increased repulsive interactions, which should further constrain the large amplitude modes that contribute the most to the vibrational entropy. In some cases, however, the opposite effect occurred; the vibrational entropy actually increased because surface crowding forced adsorbates to different binding locations that had lower frequencies. Our results highlighted cases where coverage-dependent entropy should be included, such as for adsorbates with lateral vibrational modes and systems at high temperatures. These methods for including coverage-dependent properties into mean-field microkinetics in a thermodynamically consistent way are now available in the open-source software Cantera.