Coverage-dependent kinetics and thermodynamics of carbon monoxide adsorption on a ternary copper catalyst derived from static adsorption microcalorimetry

A reliable method for adsorption systems in equilibrium is established to derive coverage-dependent kinetics and thermodynamics from the volumetric data obtained during the static microcalorimetric measurement of heats of adsorption. The Wigner-Polanyi equation is applied to analyze the pressure change as a function of time during stepwise dosing of the adsorptive until thermodynamic adsorption-desorption equilibrium is established. For carbon monoxide adsorption on a hydrogen-reduced Cu/ZnO/Al₂O₃ catalyst, the adsorption rate constant (k_a) is found to be in the range from 10^-6 to 10^-4 Pa^-1 s^-1, and the desorption rate constant (k_d) from 10^-4 to 10^-2 s^-1, both increasing with fractional coverage θ. The kinetically derived equilibrium constant K(θ) is in good agreement with K(θ) obtained from the adsorption isotherm. RT ln(Kp⁰) and the differential heat of adsorption (q^diff) were found to decrease in parallel, reflecting a normal Temkin-type heterogeneity.