STRUCTURE AND CHARACTERIZATION OF SUPPORTED RUTHENIUM-COBALT BIMETALLIC CATALYSTS

Ruthenium, cobalt, and ruthenium-cobalt bimetallic samples, supported on SiO2, Al2O3, and NaY zeolite, were characterized by temperature-pro grammed reduction, CO chemisorption, X-ray diffraction, X-ray photoele ctron spectroscopy, and transmission electron microscopy, Temperature- programmed reduction revealed that the reducibility for cobalt increas es in the order NaY < SiO2 < Al2O3, while for ruthenium the sequence w as Al2O3 < NaY < SiO2. If Ru/NaY samples are calcined in oxygen, then ruthenium migrates to the external surface of NaY and agglomerates, wh ile in the case of He-treated zeolite samples the ruthenium metal part icles are stabilized in the supercage in the range of 1 to 3 nm averag e diameter, as measured by X-ray diffraction, CO chemisorption, and tr ansmission electron microscopy. Cobalt ions are irreducible when they are exchanged alone or first in the NaY zeolite for the bimetallic sam ple Ru-Co/NaY[I]. Here the reduction of Ru3+ ions is not affected by t he presence of cobalt, whereas when Ru3+ ions exchanged rst Into NaY ( Ru-Co/NaY[II]), the cobalt ions are easily reduced and bimetallic part icles are formed but the migration of ruthenium particles to the outer surface of NaY zeolite is hampered. (C) 1997 Academic Press.