Yutaka Morikawa

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.

Propane selective oxidation over monophasic Mo-V-Te-O catalysts prepared by hydrothermal synthesis

Two distinct phases, orthorhombic and hexagonal, of Mo–V–Te–O mixed oxide catalysts were prepared separately by the hydrothermal synthetic method and solid-state reaction, and these catalysts were tested for propane selective oxidation to acrylic acid. The hydrothermally synthesized orthorhombic phase of the Mo–V–Te–O catalyst showed high activity and selectivity for the oxidation of propane into acrylic acid. This catalyst also showed extremely high catalytic performance in the propene oxidation, producing acrylic acid in a high yield. The hexagonal Mo–V–Te–O catalyst was formed via the solid-state reaction between the orthorhombic Mo–V–Te–O and α-TeVO4. This phase showed poor activity to both propane and propene oxidations, although the hexagonal phase was constructed with the octahedra of Mo and V similar to the orthorhombic phase. Reaction kinetics study over the catalyst with orthorhombic structure revealed that propane oxidation was of first order with respect to propane and nearly zero order with respect to oxygen, suggesting that the rate-determining step of the reaction is C–H bond breaking of propane to form propene. Structural effects on the catalytic oxidation performance were discussed.

Condensation of alcohol over solid-base catalyst to form higher alcohols

Condensations of various primary alcohols (C2-C5) with methanol were carried out at atmospheric pressure over various metal oxides having a solid-base property. The reactions gave one or two carbon higher alcohol than the reacted primary alcohol. MgO catalyst was most active for the reaction and yielded the alcohol products in high selectivity (> 80%). Based on the results of the exchange reaction between methyl hydrogen of methanol over MgO surface, it is concluded that a rapid hydride transfer between adsorbed alcohol and adsorbed carbonyl is responsible for the selective formation of alcohols.

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.

Displacement of adsorbed nitrogen accompanied by isotopic mixing over unpromoted iron

Abstract The displacement process of adsorbed nitrogen was isotopically traced by measuring the time course of isotopic concentration in the gas phase after an abrupt change, holding the equilibrium condition for the adsorption. The isotopic mixing in nitrogen was also observed. The rate of displacement was much larger than that of the mixing. This finding provides evidence that a portion of adsorbed nitrogen desorbs without mixing. There must be some undissociated nitrogen adsorbed, the amount of which seems to reach more than 80% of the adsorbed nitrogen.

Tracer studies of catalytic oxidation by bismuth molybdate: II. Propylene reduction of labeled catalysts and catalytic oxidation of propylene

Differently 18O-labeled bismuth molybdate catalysts were prepared by the solid-state reaction from 18O-enriched bismuth and molybdenum oxides. The results of the propylene reduction of the catalysts and the catalytic oxidation of propylene clearly demonstrated that the oxygen atom in the acrolein formed comes from the (Bi2O2)n2+ layer whether or not the gaseous oxygen is present. During the catalytic oxidation, the oxide ions consumed by the reaction seem to be replenished by gaseous oxygen through the (MoO2)n2+ layer.

Studies on the reduction-reoxidation of bismuth molybdate catalysts by temperature programmed reoxidation method

Abstract A new method of temperature programmed reoxidation (TPR) which gives a correlation of reoxidation rates with temperature in curved lines was devised and applied to slightly reduced MoO3, Bi2O3 and bismuth molybdate catalysts. Those oxide catalysts are found to be characterized by peaks in TPR. That is, MoO3 and Bi2O3 give TPR peaks at 410 and 180 °C, respectively. An increase in the extent of prereduction results in another peak with both oxides, indicating that reoxidation takes place in two steps. Bismuth molybdate catalysts of different compositions give different peaks which may be identified as composites of three TPR peaks. Every bismuth molybdate catalyst which gives the TPR peak at 320 °C is invariably active for selective oxidation of propylene to acrolein. The addition of phosphoric acid to bismuth molybdate catalysts increases the peak area at 320 °C and consistently enhances the formation of acrolein from propylene. The activation energies were determined for reduction of bismuth molybdate catalysts, reoxidation of slightly reduced catalysts and catalytic oxidation of propylene to acrolein. Those values are correlated to the TPR peak.

A low-pressure guerbet reaction over magnesium oxide catalyst

Propan-1-ol and 2-methylpropan-1-ol were synthesized selectively by the catalytic reaction of methanol and ethanol over magnesium oxide.

Solid base-catalyzed reaction of nitriles with methanol to form α,β-unsaturated nitriles I. Conversion and selectivity

Abstract The synthesis of α,β-unsaturated nitriles from saturated nitriles and methanol was achieved with basic metal oxide catalysts activated by transition metal ions. The methyl or methylene groups at the α-position of saturated nitriles are converted to a vinyl group. The reaction proceeds via dehydrogenation of methanol, cross coupling, and dehydration. Magnesium oxide, activated by manganese ion or chromium ion, has been found to give the most effective catalytic performance. In the conversion of acetonitrile, the selectivity to acrylonitrile was more than 95%. This method was also useful for the conversion of propionitrile to methacrylonitrile.

Catalytic oxidative dimerization of methane to form C2-compounds over Arppe's phase oxychlorides of Bi, La and Sm

Three distinct examples of Arppes phase (M24O31Cl10; M = Bi, La, Sm), which has a structure related to that of the layered oxychloride BiOCl, have been used as monophasic catalysts for the oxidative dehydrogenation of CH4. The stability and performance of these rival those of the best catalysts previously reported.