Structure and characterization of supported ruthenium-cobalt bimetallic catalysts

Ruthenium, cobalt, and ruthenium-cobalt bimetallic samples, supported on SiO{sub 2}, Al{sub 2}O{sub 3}, 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 < SiO{sub 2} < Al{sub 2}O{sub 3}, while for ruthenium the sequence was Al{sub 2}O{sub 3} < NaY < SiO{sub 2}. 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. Here, the reduction of Ru{sup 3+} ions is not affected by the presence of cobalt, whereas when Ru{sup 3+} ions exchanged first into NaY (Ru-Co/NaY), 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. 52 refs., 6 figs., 6 tabs.