DIFFUSE-REFLECTANCE IR-SPECTROSCOPY EVIDENCE OF THE UNUSUAL PROPERTIES OF PLATINUM IN PT MG(AL)O CATALYSTS FOR THE SELECTIVE AROMATIZATION OF N-ALKANES/

Diffuse reflectance IR spectra of CO adsorbed on Pt/Mg(Al)O catalysts were studied at room temperature and different surface coverages of me tallic Pt. They show the existence of two types of metallic Pt particl es. One type has a normal behavior toward the adsorption of CO, which is probably related to the lower dispersion of Pt. The other type prob ably corresponds to smaller negatively charged clusters like those fou nd for Pt-loaded alkaline and alkaline-earth forms of zeolites. They a re characterized by the very low frequency of the singletone correspon ding to the linear form of adsorbed CO and high thermal stability of t he bridging complexes of CO with metallic Pt. Such by metal-support in teraction modified platinum is likely responsible for high activity an d selectivity of Pt/Mg(Al)O catalyst in n-alkanes aromatization.