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-programmed reduction, CO chemisorption, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, Temperature-programmed reduction revealed that the reducibility for cobalt increases in the order NaY < SiO2 < Al2O3, while for ruthenium the sequence was Al2O3 < NaY < SiO2. If Ru/NaY samples are calcined in oxygen, then ruthenium migrates to the external surface of NaY and agglomerates, while in the case of He-treated zeolite samples the ruthenium metal particles are stabilized in the supercage in the range of 1 to 3 nm average diameter, as measured by X-ray diffraction, CO chemisorption, and transmission electron microscopy. Cobalt ions are irreducible when they are exchanged alone or first in the NaY zeolite for the bimetallic sample Ru-Co/NaY[I]. Here the reduction of Ru3+ ions is not affected by the presence of cobalt, whereas when Ru3+ ions exchanged rst Into NaY (Ru-Co/NaY[II]), the cobalt ions are easily reduced and bimetallic particles are formed but the migration of ruthenium particles to the outer surface of NaY zeolite is hampered. (C) 1997 Academic Press.