DRIFTS studies of carbon monoxide coverage on highly dispersed bimetallic Pt-Cu and Pt-An catalysts

Silica supported platinum-gold and platinum-copper catalysts prepared from organometallic cluster precursors were characterized with diffuse reflectan ce Fourier-transform spectroscopy (DRIFTS) of adsorbed CO. Because of the e ffects that dipole coupling of adsorbed carbon monoxide molecules can have on the infrared spectrum, coverage studies were employed to evaluate the in teractions between CO and the catalyst surfaces. DRIFTS spectra of the cata lysts prepared from bimetallic molecular cluster precursors showed signific antly lower C dropO stretching frequencies relative to a traditionally prep ared platinum catalyst. The lowering of the C dropO stretching frequency ma y be the result of the formation of unique alloys and particle morphologies . In the case of the catalyst prepared from the platinum-copper cluster, tw o peaks were identified in the Pt-C dropO stretching region, one of which i s postulated to be a bridging or semi-bridging mode between Pt and Cu. Infr ared spectroscopy results are also discussed in relation to kinetic data fr om the n-hexane conversion reaction. Differences in catalyst activities and selectivities are concluded to be primarily due to geometric (i.e. structu ral or morphological) effects. (C) 2001 Elsevier Science B.V. All rights re served.