Temperature Dependence of Carbon Monoxide Adsorption on a Temperature Dependence of Carbon Monoxide Adsorption on a High-Silica H-FER Zeolite
Abstract
The temperature dependence of the isosteric heat of the CO adsorption on a high-silica protonic ferrierite (H-FER) zeolite was investigated using microcalorimetry and density functional theory/coupled-cluster (DFT/CC) atomistic simulations. A large change in the experimental heat of adsorption was observed at the zero-coverage limit for the CO/H-FER system (from 32.2 kJ/mol at 200 K to 25.4 kJ/mol at 300 K).
This can be explained by a dramatic change in the CO dynamics in the 200-300 K temperature range. During our ab initio molecular dynamics simulation at 200 K, the CO molecule is localized; at 300 K, the molecule jumps between adjacent Bronsted sites.
The only exception has been found for the T-4 '' site, where the fast desorption of the CO molecule is prevented by a curved ferrierite wall enclosing this site. The previously reported variable temperature adsorption of the CO/H-FER with Si/A1 27.5 (28.4(+/- 2) kJ/mol) is consistent with the Perdew-Burke-Ernzerhof/CC predictions for individual sites when the statistical distribution of adsorption sites and temperature effects are taken into account.