Gas chromatographic study of hydrogen and hydrocarbon adsorption on platinum/alumina catalyst

Abstract

The irreversible and the reversible adsorption of hydrogen on commercial 0.3%wt Pt/Aı2O3 reforming catalyst has been studied in a gas-solid chromatograph in the temperature range 74-233 °C and 96-237 °C respectively. The reversible adsorption of two naphthenes (cyclohexane and methylcyclohexane) and of two aromatics (benzene and toluene) on the same catalyst have also been investigated between 190-236 °C. Adsorption isotherms were constructed at several temperatures for all the adsorbates studied. The elution (or the pulse) technique was used in all the experiments. From the adsorpti on isotherms heats of adsorption were calculated using constant surface coverage values at different temperatures. It was found that some hydrogen is adsorbed irreversibly within the temperature range considered and that the reversible adsorption of hydrogen is an activated process with an average heat of adsorption of 0.87 kcal/gmol (3.69 kj/kmol). The reversible adsorptions of cyclohexane, methylcyclohexane, benzene and toluene are also activated processes with average heats of adsoiption of 7.48 kcal/gmol (31.30 kJ/kmol), 7.45 kcal/gmol (31.17 kJ/kmo1), 13.11 kcal/gmol (54.85 kJ/kmol) and 13.90 kcal/gmol(58;16 kJ/kmol) respectively.