Model oxide-supported metal catalysts: energetics, particle thicknesses, chemisorption and catalytic properties

Many industrially important catalysts consist of late transition metal part icles supported on the surfaces of oxide materials. Our studies of such sys tems using model catalysts consisting of metal films vapor deposited onto t he surfaces of single-crystalline oxides are reviewed here. Systems studied include Cu on ZnO, Pt on ZnO. Au on TiO2 and Cu, Ag and Pt, on MgO. A uniq ue adsorption microcalorimeter was developed to measure directly the energe tic stability of the metal atoms on the oxide surfaces and the adhesion ene rgy at the metal/oxide interface, which clarify the structural and chemisor ption properties of the ultrathin metal particles. The structure of the oxi de surface and the metal particles was elucidated by low-energy electron di ffraction (LEED), low-energy ion scattering spectroscopy (ISS), angular-res olved X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffra ction (XPD). The electronic character of the metal particles was revealed b y XPS, Auger electron spectroscopy (AES), band-bending and work function me asurements. Sintering rates were measured by temperature-programmed ion sca ttering spectroscopy (TPISS). The chemisorption properties of these particl es and their catalytic reactivity were monitored by mass spectroscopy and t emperature-programmed desorption (TPD).