Hydrocarbon adsorption and coke formation on Pt/Al2O3 and Pt-Sn/Al2O3 catalysts

The irreversible adsorption and coke formation from methane, n-hexane, 1-hexene and 1,5-hexadiene were investigated on Pt/Al2O3 and Pt-Sn/Al2O3 between and 450°C. Depending on temperature, chemisorption, coke precursor and coke formation have been observed. Coke precursors are formed on Pt sites and transferred to alumina. Two routes of coking were observed. Presence of tin decreases the adsorption bond strength of 1-hexene and at low concentrations increases the amount chemisorbed. This phenomenon is explained by the ensemble effect. A drain-off effect is proposed to explain the decrease of the coke coverage on the metallic sites upon addition of Sn.