Hisashi Ueda

The paramagnetic species found on the surface of Al2O3MoO3CoO particles

Abstract The paramagnetic species on the surface of Al2O3MoO3CoO catalysts were studied. The ESR spectra of unsupported oxides CoO, Co2O3, Co3O4, CoAl2O4, and CoMoO4 were first studied. The ESR spectra of supported cobalt oxides were also studied. The spectra of supported oxides were different from those of the unsupported oxides, indicating that the supported cobalt ions are in a different state from those in unsupported oxides. The two-phase theory for the supported cobalt ions interprets the experimental results well. The Co2+ and Co3+ concentrations on the surface were estimated from ESR results. The desulfurization rate of Al2O3 MoO3CoO catalysts were measured together with the surface concentrations of Co2+, Co3+, Mo5+, and thionaphthol+O∗2− surface cation complex when H2 and thionaphthol were added to the surface. A simple correlation between the desulfurization rate and the concentrations of these paramagnetic species was found.

The reactivities and the stabilities of the paramagnetic species formed on the surface of Al2O3MoO3CoO and SiO2MoO3CoO: The carrier effects of Al2O3 and SiO2☆

Abstract The rates of formation and decay, the concentration and the stability of the paramagnetic species on the surface of the catalysts (carrier-MoO3, carrier-MoO3-CoO) prepared from two oxide carriers, γ-alumina and silica gel, having identical surface areas and pore radius distributions, were studied by electron spin resonance (e.s.r.) using a mixture in which an aromatic hydrocarbon was added to the oxide with or without a solvent (benzene). The measurements were made either at 20 °C or at 20 · 300 °C. The cobalt ions did not interfere with the Mo6+ ions on γ-alumina, but reduced the activity of the Mo6+ ions on silica gel. R+, a hydrocarbon cation, was formed only when Mo6+ was present, while R+O★2− a complex ion which is different from R+, can be formed in the absence of Mo6+, though its amount was increased by Mo6+. R+ appeared only in the presence of solvent molecules while R+O★2− appeared without a solvent. The stabilities of R+O★2− and Mo5+ at 300 °C were far larger on γ-alumina than on silica gel. The effects of the carriers on the activities of the hydrodesulphurisation catalysts are in accord with the catalytic reaction scheme already reported.

The axially fixed phenanthrene cation on oxide surfaces as studied by electron spin resonance

Abstract A benzene solution of phenanthrene, which had been purified by zone melting method, was mixed with γ-alumina (with 10.5% of MoO 3 supported on it), or silica gel (with 8.5% of MoO 3 supported on it), both of which had been treated at 300 °C in a vacuum of 10 −5 Torr. The phenanthrene cation thus produced was observed by esr method. In the case of silica gel, the number of protons interacting with the unpaired electron was: 1 proton with a splitting of 1.41 G, 2 with 1.97 G, 2 with 4.09 G, and 4 with 2.79 G, and the half-width was 0.07 G. In the case of γ-alumina, the number of protons interacting with the unpaired electron was: 1 proton with a splitting of 1.50 G, and 8 with 3.00 G, and the half-width was 0.57 G. The analysis of the obtained spectra has shown that a combination of four RCH 2 · radicals and a RCHR′-radical interprets them. It has been concluded that the phenanthrene cation has restricted rotational motions on an oxide surface. It has also been shown that there are three significant points in the studies of the aromatic hydrocarbon cations on the catalyst surface by esr method. (A) The interaction between adsorbed O 2 or H 2 O and the cation can be observed. (B) The exact point of the molecule at which the cation is adsorbed on the oxide surface can be known