Abstract
The adsorption of alkylaromatic hydrocarbons (normal series: Me, Et, n-Pr, and n-Bu; α-methylated series; Me, Et, i-Pr and t-Bu) has been studied, with 20 wt% nickel supported on AlPO 4, SiO 2, and Al 2O 3 catalysts by using a gas-solid chromatographic technique. Isosteric adsorption heats at low (zero) coverage (Δ H ads o), determined by measuring the retention volume of the adsorbate at different column temperatures, show that the adsorption process is exothermic (δ H ads o < 0). The Gibbs standard adsorption free energies (Δ G ads o) and standard molar adsorption entropies (Δ S ads o) are determined from the values of the Henry's law adsorption constants and show that the adsorption process is nonspontaneous (Δ G ads o > 0) and that the alkylaromatic hydrocarbons lose vibrational and rotational freedom in their adsorption on the catalyst surface (Δ S ads o < 0). In all cases the relative Henry's adsorption constants fit the Taft-Pavelich equation: log [ ( K Γ , p ) i / ( K Γ , p ) 0 ] = ρ * σ * + δ Es .
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