Atsumu Ozaki

Activation of nitrogen by alkali metal promoted transition metal I. Ammonia synthesis over ruthenium promoted by alkali metal

Abstract The rate of ammonia synthesis over ruthenium was found to be remarkably promoted by addition of alkali metal, particularly when ruthenium is supported by active carbon (AC) or alumina. The synthesis rate over the 5% RuACK catalyst can be raised to about 10 times that of conventional doubly promoted iron (Fe Al 2 O 3 K 2 O) catalyst at 250 °C. RuACCs gives even greater activity than RuACK. The catalytic activity increases with decrease in ionization potential of added alkali (Cs > K > Na) and with increase in the added amount of alkali metal, approaching a plateau value at around 3–4 mg-atom alkali/g-catalyst. Unsupported ruthenium is also remarkably promoted by addition of alkali metal. It is accordingly concluded that the promoter action is provided by a charge transfer from alkali metal to transition metal which brings about a higher electron density in the transition metal, a favorable state for the activation of nitrogen. The specific synthesis rates per surface ruthenium are higher over active carbon and alumina than other supports, suggesting a role of these supports as a medium of electron transfer.

Acid-base properties and catalytic activity of solid surfaces

Abstract Acid-base propeities of the solid surfaces, oxides, sulfates, and acid phosphates, and their catalytic behavior for the hydration of propylene, the polymerization of isobutylene and the polymerization of acetaldehyde are discussed in terms of a generalized electronegativity of the metal ion (Xi). It is found that the acidity and the catalytic activity increase with the parameter Xi. Such general trends are explained by the inductive effect of the metal ions in the catalysts.

Support and promoter effect of ruthenium catalyst. II: Ruthenium/alkaline earth catalyst for activation of dinitrogen

The turnover frequency (TOP) of the ammonia synthesis on Ru was promoted by using alkaline earths as supports. The TOF of this reaction on RuMgO and RuCaO was as high as those on RuCsOHAl2O3 catalyst. The activity was shown to be correlated with the electronegativity of oxide support. XPS results seem to support the electron transfer from alkaline earth to Ru. Activity of RuMgO was further promoted with CsOH, which increased not only TOF but also Ru dispersion. On the other hand, Ru/alkaline earth with K, which may be called “superbase-supported Ru catalysts,” proved to have excellent activities for N2 activation. TOF of ammonia synthesis over those catalyst was as high as that on RuKAC (activated carbon) which has been known to be the best catalyst under these conditions. Furthermore, TOF of N2 isotopic equilibration reaction on these catalyst were several times as high as those on RuKAl2O3 or RuKAC which have been believed to be the most active catalysts for this reaction.

Regularities in catalytic properties of metal oxides in propylene oxidation

The reaction of propylene with oxygen to form mainly carbon dioxide was studied over a number of metal oxide catalysts by means of a differential reactor. Kinetic quantities, such as the reaction rate at 300°C, reaction orders in both reactants, and Arrhenius parameters were determined. These quantities were found to be correlated with each other, and, to some extent, with the heat of formation of the catalyst oxides divided by the number of oxygen atoms in the oxide molecule (Δ H o ). That is, the larger the Δ H o , the less active the catalyst, and the higher the order in propylene. A higher order in propylene may suggest a higher oxygen coverage over the catalyst surface.

Support and promoter effect of ruthenium catalyst: I. Characterization of alkali-promoted ruthenium/alumina catalysts for ammonia synthesis

RuAl2O3 catalysts promoted with various alkali precursors were prepared and characterized by various methods including XPS and TPR (temperature-programmed reduction) techniques. The activation of the promoted catalyst was studied in detail. The addition of an alkali precursor, especially CsNO3, promoted the turnover frequency (TOF) of ammonia synthesis, and also increased þe Ru dispersion. It is suggested that the alkali precursor became converted to hydroxide after reduction at 400 °C. The promotion of TOF by alkali corresponded to the electron-donating tendency (CsOH > KOH). Ru-alkali(KOH)Al2O3 was found to be tolerant to CO and/or H2O poisoning, and treatment in H2 led to restoration of the original catalytic activity.

Regularity in the catalytic properties of metal oxides in hydrocarbon oxidation

The catalytic properties of various oxides were determined in the oxidation of isobutene, acetylene, ethylene, and propane and were correlated with the heat of formation of the catalyst oxides divided by the number of oxygen atoms in the oxide molecule (ΔHO). It was observed there is a distinctive relation between catalytic activity and ΔHO; the lower the ΔHO of the catalyst, the higher its activity. For isobutene and acetylene oxidations, the reaction order in hydrocarbon increased and that in oxygen decreased with increasing ΔHO, whereas for ethylene and propane both orders in oxygen and hydrocarbon were insensitive to ΔHO. Some experiments on competitive oxidation of hydrocarbons were undertaken, and it was concluded that the hydrocarbon reacts via the adsorbed state. The sequence of adsorption strength was determined as iso-C4H8 > C2H2 > C3H6 > C2H4 > C3H8, which is the reverse of the reaction order sequence.

The effective site on acid catalysts revealed in n-butene isomerization

1-Butene isomerization experiments were carried out at near room temperatures with deuterated acid catalysts such as silica-alumina, silica-magnesia, silica-zirconia, nickel oxide-silica, alumina, alumina-boria, and nickel sulfate-on-silica, as well as with nondeuterated catalysts in the presence of deuterated propylene or other hydrocarbons. Reaction mixtures were separated by gas chromatographic column and analyzed for deuterium distribution by mass spectrometry. The exchange behavior revealed in the experiments was remarkably dependent on the evacuation temperature of the deuterated catalysts. For the evacuation temperatures near 100 °C, most of the deuterated catalysts gave deuterated products, the deuterobutene concentrations found in product 2-butenes being much larger than in unreacted 1-butene. However the larger deuterobutene concentrations in 2-butenes decreased with a rise in the evacuation temperature of the deuterated catalysts, down to negligible concentration for the evacuation at 500 °C, whereas the conversions of reactant increased with rise in the evacuation temperature above 100 °C. On the other hand, with most of the nondeuterated catalysts evacuated at 500 °C, 1-butene isomerization in the presence of deuteropropylene revealed an essentially identical behavior of hydrogen exchange with that on the deuterated catalysts evacuated at 100 °C. These results suggest that n-butene isomerization on these catalysts proceeds at least partly through a proton donor-acceptor mechanism with either Bronsted acids on the surface or the carbonium ions formed by adsorption of olefins on Lewis acid sites serving as proton donors, although the conclusion is open to question in the case of alumina.

Acidity of nickel silicate and its bearing on the catalytic activity for ethylene dimerization and butene isomerization

Abstract Catalytic activities of nickel silicates (montmorillonite and antigorite) for ethylene dimerization and butene isomerization run parallel when the catalysts are activated by evacuation at elevated temperatures, giving two maximums in activities. The variations in catalytic activities are closely correlated to the acidity of catalysts. The acid site responsible for the catalytic activity is protonic on montmorillonite, while nonprotonic on antigorite, as evidenced by the effect of water content or of sodium ion contamination, and the infrared spectra of adsorbed pyridine. This was confirmed by incorporation of proton held by the montmorillonite into the initial product of ethylene dimerization, 1-butene.

Tracer study of ethylene dimerization over nickel oxide-silica catalyst

The role of proton originally held by the catalyst NiOSiO2 in the dimerization of ethylene was investigated by means of the deuterium tracer, taking the subsequent isomerization of butene into consideration. It was shown that the deuterium involved in the catalyst did appear in the product butene by way of the isomerization and not of the dimerization. Further study on the dimerization in the presence of C3D6 or C2D4 revealed that the reacting ethylene molecules rapidly exchange their hydrogen with each other prior to the dimerization. A few micromoles of carbon monoxide adsorbed completely prevented both the isotopic exchange and the dimerization. The mechanism of the dimerization is discussed on the basis of these results. It is suggested that the active site responsible for the dimerization consists of a low valent nickel and an acid.

Catalytic oxidation of olefin over oxide catalysts containing molybdenum: III. Oxidation of olefin to ketone over Co3O4MoO3 and SnO2MoO3 catalysts

Oxidation of various olefins and some related hydrocarbons over Co3O4MoO3 and SnO2MoO3 (Co or Sn:Mo = 9:1) are described. Both binary oxides are effective catalysts for the oxidation of olefins to corresponding ketones, while SnO2MoO3 is the better one. Propylene is converted to acetone at 100–160 °C with more than 90% selectivity over SnO2MoO3. n-Butenes and 1-pentene are oxidized to methyl ethyl ketone and methyl propyl ketone (including diethyl ketone), respectively. However, ethylene is converted exclusively to carbon dioxide. Isobutene, which has no corresponding ketone, is converted to t-butyl alcohol and diisobutene over SnO2MoO3 and to α-methyl acrolein over Co3O4MoO3. On the other hand, primary and secondary alcohols are easily oxidized to corresponding aldehyde and ketone, respectively, over both catalysts. The ketone formation is concluded to proceed via oxyde-hydrogenation of alcohol or alcoholic intermediate formed by hydration of olefin. The active site seems to involve an acidic point which is formed by the combination of tin or cobalt oxide with molybdenum trioxide.