Tsuneo Ikawa

The acid-base properties of MoO3Bi2O3P2O5 catalysts and their correlation with catalytic activity and selectivity

Abstract The amounts of both the acidic and basic sites of MoO 3 Bi 2 O 3 P 2 O 5 catalysts over a full range of Bi Mo ratios were measured by studying the adsorption of basic and acidic molecules, respectively, in the gas phase. The results obtained by the pulse method agreed well with those obtained by the static method. The acidity of pure Bi 2 O 3 is far lower than that of MoO 3 P 2 O 5 , and with an increase in the Bi 2 O 3 content, the acidity rapidly increases at first, passes through a maximum at the Bi Mo atomic ratio of 1–2, and then decreases. On the other hand, the basicity of MoO 3 P 2 O 5 is fairly low compared with that of pure Bi 2 O 3 ; the basicity of the catalyst gradually increases with the Bi 2 O 3 content. The relationship between the acid-base properties obtained here and the catalytic behavior obtained previously was investigated. The oxidation and isomerization activities for olefins are proportional to the acidity of the catalyst, and the oxidation activity for an acidic compound and hydrogen is connected with the basicity. The selectivity of the catalyst was also interpreted in connection with the acid-base properties. Finally, the characters of the active sites were discussed, together with those of the acidic and basic sites.

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.

Study of ternary-component bismuth molybdate catalysts by 18O2 tracer in the oxidation of propylene to acrolein

Participation of lattice oxide ions of ternary-component bismuth molybdate catalysts M-Bi-Mo-O (M = Ni, Co, Mg, Mn, Ca, Sr, Ba, and Pb) was investigated using the /sup 18/O/sub 2/ tracer in the selective oxidation of propylene to acrolein. The participation of the lattice oxide ions in the oxidation is prominent on every catalyst but the extent of the participation varies significantly depending on the structure of the catalyst. Only lattice oxide ions in the bismuth molybdate phase are incorporated into the oxidized products on the catalysts (M = Ni, Co, Mg, and Mn) where M have smaller ionic radius than Bi/sup 3 +/; catalyst particles are composed of a shell of bismuth molybdates and a core of MMoO/sub 4/. On the other hand, whole oxide ions in the active particles are involved in the oxidation on catalysts having a scheelite-type structure (M = Ca, Sr, Ba, and Pb) where M has a comparable ionic radius to Bi/sup 3 +/.

Novel peparation of silyl enol ethers from allyl alcohols

Abstract A novel synthetic method for silyl enol ethers from allyl alcohols was developed using ruthenium hydride catalyst.

Solid base-catalyzed reaction of nitriles with methanol to form α,β-unsaturated nitriles. II, Surface base property and reaction mechanism

Abstract Solid acid and base properties of magnesium oxides activated by transition metal ions, MMgO, which are effective catalysts for the reaction of nitriles with methanol to form corresponding α,β-unsaturated nitriles, were studied by temperature-programmed desorption of CO2 and the reaction of isopropyl alcohol, and the reaction mechanism was studied by isotopic tracer methods. The surface base property of magnesium oxide was modified by the addition of a metal ion; the addition of a metal ion with larger ionic radius than Mg2+ increases the amount of surface base site, whereas the addition of a metal ion with an ionic radius smaller than that of Mg2+ induces surface acid sites without any appreciable changes in the amount of surface base site. Active catalysts were formed in the latter case but not in the former case. It was thought that a surface acid property as well as a surface base property played an important role in the course of the reaction. Reaction of deuterium-substituted acetonitrile and methanol revealed that the exchange reaction between hydroxyl hydrogen of methanol and methyl hydrogen of acetonitrile took place readily under the conditions of acrylonitrile synthesis and the isotopic distribution in acetonitrile after the reaction was very close to that of isotopic equilibrium. No exchange reaction between methyl hydrogen of methanol and that of acetonitrile was observed. It was found, on the other hand, that the isotopic exchange reaction between methyl hydrogen of deuterated methanol and light methanol can occur under the same conditions. The reaction mechanism appears to be dehydrogenation of methanol to adsorbed formaldehyde which then reacts with the acetonitrile anion and, after dehydration, yields acrylonitrile.

Catalytic properties of tricomponent metal oxides having the scheelite structure: II. Structural stability in the reduction-oxidation cycle

Structural stability of complex metal oxide catalysts having the scheelite structure, Bi1 − x3V1 − x MoxO4, in the reduction-oxidation cycle is discussed on the basis of the mobility of lattice oxide ions determined by 18O2 tracer measurements. Reduction of BiVO4 and BiVMoO with a lower content of molybdenum, where the mobilities of lattice oxide ions are low, takes place in the vicinity of the surface layer of oxide, so that the surface structure is significantly changed after the reduction-oxidation cycle. The catalysts which contain the higher amounts of molybdenum are found to be stable during the reduction-oxidation process because rapid migration of lattice oxide ions prevents the local reduction of the catalysts.

Stereoselective synthesis of tetrahydrofuran-3-carbaldehyde

Abstract Trans-tetrahydrofuran-3-carbaldehydes are prepared by ruthenium-catalyzed isomerization of 4,7-dihydro-1,3-dioxepines and subsequent Lewis acid-catalyzed 1,3-alkyl migration.

Catalytic isomerization of acetylenic silyl ethers to dienol silyl ethers by ruthenium hydride complexes

Abstract Acetylenic silyl ethers are converted catalytically to the corresponding conjugated dienol silyl ethers by ruthenium hydride complexes.

A hydroperoxorhodium complex: Oxidation of the coordinated triphenylphosphine

Abstract A novel hydroperoxorhodium complex, (Ph 3 P) 2 (acac)ClRhOOH, has been prepared by treatment of the peroxorhodium complex (Ph 3 P) 3 ClRh(O) 2 with acetylacetone (acacH) in benzene. The stretching vibration of the OO bond is proven to appear at 813 cm −1 by comparison with that of the 18 O 2 -labeled complex. The hydroperoxorhodium complex decomposes in chloroform in the presence of triphenylphosphine to (Ph 3 P) 2 (acac)RhCl 2 via the corresponding hydroxo complex, with oxidation of the coordinated triphenylphosphine.

Study of tellurium oxide catalysts by 18O2 tracer in the oxidation of propylene to acrolein

Abstract Participation of the lattice oxide ions in various tellurium-based multicomponent oxide catalysts, M-Te-Mo-O (M = Co, Mn, Fe, and Cu) was investigated using the 18O2 tracer in the selective oxidation of propylene to acrolein. The participation of the lattice oxide ions in the oxidation is quite prominent on every catalyst, beyond 100 layers of the lattice, and is comparable to that observed on bismuth molybdate catalyst system. The combination of the transition metal oxide as a third component with the binary oxide, Te-Mo-O increases the rate of diffusion of the lattice oxide ion. Clear correlation was observed between the degree of evaporation of tellurium element and the number of oxide ion layer involved in the oxidation. These results suggest that high mobility of the lattice oxide ions in this catalyst plays an important role in suppressing the vaporization of tellurium from the catalyst during oxidation.