Studies of the roles of Sn or Fe on γ-Al2O3-supported Pt catalysts by CO adsorption microcalorimetry and dehydrogenation reaction of C4 alkanes

CO adsorption microcalorimetry was employed in the study of gamma-Al2O3-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the Pt/gamma-Al2O3 catalyst was 125 kJ/mol. As CO coverage increased, the differential heat of adsorption decreased. At higher coverages, the differential heat of adsorption decreased significantly. 60% of the differential heat of CO adsorption on the Pt/gamma-Al2O3 catalyst was higher than 100 kJ/mol. No significant effect on the initial differential heat was found after adding Sn and Fe to the Pt/gamma-Al2O3 catalyst. The amount of strong CO adsorption sites decreased, while the portion of CO adsorption sites with differential heat of 60-110 kJ/mol increased after increasing the Sn or Fe content. This indicates that the surface adsorption energy was changed by adding Sn or Fe to Pt/gamma-Al2O3. The distribution of differential heat of CO adsorption on the PI-Sn(C)/gamma-Al2O3 catalyst was broad and homogeneous. Comparison of the dehydrogenation performance of C-4 alkanes with the number of CO adsorption sites with differential heat of 60-110 kJ/mol showed a good correlation. These results indicate that the surface Pt centers with differential heats of 60-110 kJ/mol for CO adsorption possess superior activity for the dehydrogenation of alkanes.