Yoshihiko Moro-oka

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.

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.

Multicomponent Bismuth Molybdate Catalyst: A Highly Functionalized Catalyst System for the Selective Oxidation of Olefin

Publisher Summary This chapter focuses on the multicomponent bismuth molybdate catalyst which is a highly functionalized catalyst system for the selective oxidation of olefin. Some progress is made in explaining the splendid catalytic performance of multicomponent bismuth molybdates that are used widely for the industrial oxidations and ammoxidations of lower olefin. The catalytic activity and selectivity are enhanced by the multifunctionalization of the catalyst systems. Many functions newly introduced are deeply associated with lattice vacancies formed by the introductions of third and fourth elements. The design of the excellent oxidation catalyst depends seriously on the method of selecting these additives by considering their valencies, electronegativities, and ionic radii. The rapid migration of oxide ion and electron transfer are also important in enhancing the catalyst stability. Thus, the appropriate introduction of additional elements into the catalyst system makes it more flexible and durable under the working conditions.

Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands TpMe2,X (X=Me, H, Br) and TpiPr2

Reaction of the dinuclear M(II)-bis(mu-hydroxo) complexes of nickel and cobalt, [(M(II)(TpR)]2(mu-OH)2] (M = Ni; 3Ni M = Co: 3Co), with one equivalent of H2O2 yields the corresponding M(III)-bis(mu-oxo) complexes, [[M(III)(TpR)]2-(mu-O)2] (M=Ni; 2Ni, M=Co: 2Co). The employment of a series of TpMe2,X (TpMe2,X = hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate; X = Me, H, Br) as a metal supporting ligand makes it possible to isolate and structurally characterize the thermally unstable M(III)-bis-(mu-oxo) complexes 2Ni and 2Co. Both the starting (3Ni and 3Co) and resulting complexes (2Ni and 2Co) contain five-coordinate metal centers with a slightly distorted square-pyramidal geometry. Characteristic features of the nickel complexes 2Ni, such as the two intense absorptions around 400 and 300 nm in the UV-visible spectra and the apparent diamagnetism, are very similar to those of the previously reported bis(mu-oxo) species of Cu(III) and Ni(III) with ligands other than TpR, whereas the spectroscopic properties of the cobalt complexes 2Co (i.e., paramagnetically shifted NMR signals and a single intense absorption appearing at 350 nm) are clearly distinct from those of the isostructural nickel compounds 2Ni. Thermal decomposition of 2Ni and 2Co results in oxidation of the inner saturated hydrocarbyl substituents of the TpR ligand. Large kH/kD values obtained from the first-order decomposition rates of the TpMe3 and Tp(CD3)2,Me derivatives of 2 evidently indicate that the rate-determining step is an hydrogen abstraction from the primary C-H bond of the methyl substituents. mediated by the M(III)2-(mu-O)2 species. The nickel complex 2Ni shows reactivity about 10(3) times greater than that of the cobalt analogue 2Co. The oxidation ability of the M(III)(mu-O)2M(III) core should be affected by the hindered TpR ligand system, which can stabilize the +2 oxidation state of the metal centers.

Catalytic properties of tricomponent metal oxides having the scheelite structure: I. Role of bulk diffusion of lattice oxide ions in the oxidation of propylene

Kinetic measurements and 18O2 tracer studies for evaluating the participation of lattice oxide ions in the oxidation of propylene were carried out for a series of tricomponent metal oxide catalysts having the scheelite structure, Bi1 − x3V1 − xMoxO4. Catalytic activity of the scheelite oxide catalysts tested increased with the substitution of V5+ ion by Mo6+ ion without changing the selectivity. The kinetic parameters of propylene oxidation to acrolein were found to be unchanged according to Mo content (reaction orders: 1 for propylene and 0 for oxygen, activation energy: 19 ± 0.5 kcal/mol), indicating that the increase of catalytic activity was mainly attributed to the increase of active sites. 18O2 tracer studies revealed that lattice oxide ions were exclusively incorporated to form acrolein and CO2. The diffusion rate of lattice oxides ions in the oxide bulk increased with the increase of X, and then decreased through the maximum at X = 0.45. Good agreement was obtained between the catalytic activity and the mobility of lattice oxide ions. On the basis of the results, the role of the diffusion of lattice oxide ions in the catalytic oxidation is discussed.

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.

New aspects of the cobalt-dioxygen complex chemistry opened by hydrotris(pyrazoly)borate ligands (TpR): unique properties of TpRCo-dioxygen complexes

Abstract Recent advances in the chemistry of cobalt-dioxygen and related complexes supported by hydrotris(pyrazolyl)borate ligands (TpR) are reviewed. The unique properties of inorganic and organometallic TpRCo complexes clearly indicate that hindered TpR ligands carrying alkyl substituents on the pyrazolyl groups can stabilize the coordinatively unsaturated, low valent cobalt species, and that the reactivity of the coordinatively unsaturated species is influenced by steric hindrance of TpR. The unusual low-valent metal-peroxo and high-valent metal-oxo species such as CoII-superoxo, -alkylperoxo and dinuclear CoIII-bis(μ-oxo) complexes are characterized. The high-valent metal-oxo species, [TpRCoIII]2(μ-O)2, are capable of abstracting the H atom from the alkyl groups proximal to the bimetallic bis(μ-oxo) core. In the hydrotris(3,5-diisopropyl-1-pyrazolyl)borate ligand system (TpPr2i), oxygenation of the proximal isopropyl substituents on TpPr2i is mediated by the CoIII2-(μ-O)2 and CoIIOOX (X=alkyl, H) species.

Bio-inorganic approach to hydrocarbon oxidation

Abstract Oxidation reactions mimicking the biological oxidative processes are summarized. A dioxygen molecule can be activated by way of reductive activation within a coordination sphere of transition metal complexes, and the resulting electrophilic oxo species, which can also be generated by treatment with an oxo transfer reagent (so-called “shunt path”), exhibit oxidizing ability just like an oxene species.

Selective ammoxidation of propane involving homogeneous and heterogeneous steps over multicomponent metal oxide catalysts

Abstract Partial oxidation of propane to acrolein was studied using various mixed metal oxide catalysts under high partial pressures of propane and oxygen. Scheelite-type oxide catalysts containing both molybdenum and bismuth were found to be effective for the selective oxidation of propane to acrolein. Among the scheelite-type catalysts, bismuth vanadomolybdates showed the highest catalytic performance, which was further improved by the incorporation of silver ions into the catalyst. Use of the silver-doped bismuth vanadomolybdate catalyst gave a selectivity to acrolein of more than 60% at 13% conversion of propane. Studies on the effects of reaction variables suggest that the reaction may proceed via propylene as an intermediate, the propylene being formed from propane in a non-catalytic radical process.

Propane oxidation over various metal molybdate catalysts

Abstract Catalytic activities of various metal molybdates were tested for the gas-phase partial oxidation of propane with molecular oxygen under an atmospheric pressure in the temperature range 325–500°C. Metal molybdate catalysts were found to mostly promote the oxidative dehydrogenation of propane to propene. More than 80% selectivity to propene was attained on each catalyst but their catalytic activities differed greatly. Of the catalysts, cobalt molybdate showed the highest catalytic performance for the oxidative dehydrogenation and the catalytic property strongly depended on the catalyst composition. Co 0.95 MoO x catalyst gave 60% selectivity to propene at 20% conversion of propane at 450°C. The catalytic activity and selectivity of each catalyst in the propane oxidation is discussed in terms of surface acidity and reactivity of lattice oxide ions.