Adsorption of alkylaromatic hydrocarbons on AlPO 4, Al 2O 3, and SiO 2 catalysts

Abstract

The adsorption of alkylaromatic hydrocarbons (normal series (R = Me, Et, n-Pr, and n-But) and α-methylated series (R = Me, Et, i-Pr, and t-But)) on AlPO 4, Al 2O 3, and SiO 2 catalysts have been studied using a gas-solid chromatographic technique. Adsorption heats at low (zero) coverage have been determined by measuring the retention volume of the adsorbate at different column temperatures while Δ G and Δ S values were calculated from the Δ H together with the adsorption constants ( K Γp). The adsorption process was exothermic (Δ H < 0) and nonspontaneous (Δ G > 0). In both cases, the relative adsorption constants fit the Taft equation log(K Γp ) i (K Γp ) 0 = ρ ∗σ ∗ + δE s , electrical effects being the primary influence in the α-methylated series while steric effects went into action only in the normal series.