Hydrogen adsorbed species at the metal/support interface on a Pt/Al2O3catalyst

Hydrogen chemisorption has been used to characterize an alumina-supported highly dispersed platinum catalyst. Perfect agreement between the static volumetric method and the pulse chemisorption technique for hydrogen adsorption at 298 K is proof that slow hydrogen spillover does not enhance the ratio H/Pt. However, it has been found, by means of isotopic labelling, that hydrogen molecules activated on the platinum surface are able to exchange with protons of the hydroxy groups of the support during both reduction in hydrogen at 673 K and the temperature ramp of the temperature-programmed desorption (TPD) into vacuum experiments. Three species of hydrogen adsorbed at 298 K have been identified. Based on comparison with the literature, these species have been assigned to dissociative chemisorption of hydrogen on central platinum atoms and kink platinum sites and to interfacial hydrogen. A fourth species, due to hydrogen spillover, is formed during catalyst reduction.