Adsorption of CO₂ on Gold Surfaces: Adsorbate Density Assumption Investigated Using Molecular Dynamics Simulations

M Sekulla and M Kohns and M Richter, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 62, 19884-19892 (2023).

DOI: 10.1021/acs.iecr.3c01993

Nowadays, the most accurate measurements of fluid densities near the saturated-vapor line are carried out with gravimetric measurement techniques. Such density measurements are affected by sorption effects, whose influence on the measurement data increases as the saturated-vapor line is approached. Here, we show for the first time by using the adsorption of CO2 on gold surfaces as an example of how molecular dynamics simulations can be used to reproduce and thus study the adsorbed phase on the various surfaces within the measurement cell of an experimental system. The simulations are in very good agreement with accurate experimental adsorption data. The density of the adsorbate is analyzed as a function of the temperature and the proximity to the saturated-vapor line. It has been found that for densities close to the saturated-vapor density, the average adsorbate density approaches, but never reaches, the saturated-liquid density. The error made by applying the widely used assumption that the adsorbate density equals the saturated-liquid density is investigated in detail.

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