SLOW UPTAKE OF OXYGEN AND CARBON-MONOXIDE BY PLATINUM SILICA (EUROPT-1) AND SUBSEQUENT EFFECTS ON HYDROGENATION OF BENZENE AND HYDROGENOLYSIS OF METHYLCYCLOPENTANE

Slow, activated processes, repeatedly observed in chemisorption studies with supported metals, were specifically investigated in the slow uptake of oxygen and carbon monoxide by a platinum/silica catalyst of high dispersion (EUROPT-1) and a catalyst of lower dispersion (sintered EUROPT-1). It is shown that exposure to oxygen at 400°C leads to incorporation of oxygen, which in turn causes enhanced activity towards benzene hydrogenation. In the slow carbon monoxide adsorption process, occurring already at room temperature in addition to a fast adsorption of carbon monoxide, a tightly bound adspecies is formed, whose fraction of total carbon monoxide adsorption is higher on the catalyst of higher dispersion. The coverage of the corresponding surface sites causes a selectivity change in the hydrogenolysis of methylcyclopentane towards less n-hexane formation. Based on these results, the sites responsible for this tightly bound carbon monoxide species are deduced to be located at the phase boundary platinum/support.