Yoshio Ono

Catalysis in the production and reactions of dimethyl carbonate, an environmentally benign building block

Abstract Dimethyl carbonate (DMC) is a unique molecule having versatile chemical reactivity. In many aspects, DMC is an environmentally benign building block. DMC is a safe substitute for dimethyl sulfate or methyl halides. These conventional methylating agents are toxic and corrosive and give a stoichiometric amount of inorganic by-products. Methylation with DMC is often very selective. The mono-methylation of phenylacetonitrile, O -methylation of phenol and N -methylation of aniline are such examples. The transesterification of DMC with phenol yields methyl phenyl carbonate, which gives diphenyl carbonate by further transesterification with DMC or the disproportionation. Diphenyl carbonate is an essential starting material for polycarbonates resins by “non-phosgene” process. DMC serves also as a methoxycarbonylation agent. The methoxycarbonylation of amines with DMC gives methyl carbamates, which can be converted into isocyanates by decomposition. DMC reacts with silica at 550–600 K to afford tetramethoxysilane. This gas-solid reaction gives a simple and convenient method to depolymerize silica. In this review, various aspects of the reactions of DMC and the catalysts involved in the reactions will be overviewed.

Transformation of Lower Alkanes into Aromatic Hydrocarbons over ZSM-5 Zeolites

Abstract Much attention has been paid to the transformation of lower alkanes such as propane and butanes into aromatic hydrocarbons from both industrial and academic points of view. The aromatic hydrocarbons can be utilized as a booster for high octane number gasoline and are fundamental raw chemicals in petroleum chemistry. The activation of lower alkanes is an intriguing subject. In early work, Csicsery [1–5] described dehydrocyclodimerization of lower alkanes over bifunctional catalysts such as platinum on alumina and Cr2O3 on alumina.

Transformation of propane into aromatic hydrocarbons over ZSM-5 zeolites

Transformation of propane into aromatic hydrocarbons over H-ZSM-5 and Ga-exchanged ZSM-5 (Ga-ZSM-5) zeolites were studied. Over H-ZSM-5, the mode of activation of propane changes with the conversion level of propane. Thus, propane undergoes cracking into methane and ethylene by its interaction with acidic hydroxyl groups at low conversion levels, while, at higher conversion levels, it undergoes hydride abstraction by its interaction with carbenium ions. Lower olefins thus formed give oligomerized products, which in turn, undergo dehydrogenation to give aromatic hydrocarbons. The loading of Ga3+ of ZSM-5 greatly improves the selectivity to aromatics as well as the total conversion of propane. Thus, a selectivity of 71% was obtained at 500 °C. Ga species are quite effective for the transformation of intermediate products (i.e., lower olefins) into aromatic compounds, while they have no direct role in propane activation.

Solid base catalysts for the synthesis of fine chemicals

Abstract Although catalysis by solid acids has received much attention due to its importance in petroleum refining and petrochemical processes, relatively few studies have focused on catalysis by bases. Base catalysts, however, play a decisive role in a number of reactions essential for fine-chemical synthesis. Solid-base catalysts have many advantages over liquid bases in many respects. Here, recent developments in catalysis by solid bases is described, especially regarding catalytic materials and catalytic reactions. The reactions include isomerization, aldol condensation, Knoevenagel condensation, Michael condensation, oxidation, and Si C bond formation.

Selective reactions over solid base catalysts

A variety of organic reactions are catalyzed in a very selective manner by base catalysts. Especially, solid bases offer convenient and environmentally-benign routes for organic synthesis. This review overviews the recent development on the catalysis by solid bases. The catalytic materials described are zeolites, modified zeolites, alkaline earth oxides, alkali metals on supports, KNH2 on alumina, KF on alumina, hydrotalcites and oxynitrides. Stress are also placed on novel reactions catalyzed by the solid bases. The reactions include isomerization of alkenes, reactions of alkynes, methylations, addition reactions, Knoevenagel condensations, reactions of silanes.

A survey of the mechanism in catalytic isomerization of alkanes

Abstract The isomerization of alkanes into corresponding branched isomers is one of the important processes in petroleum refining. Though the so-called bifunctional catalysts are used in industrial processes, the better catalysts are still sought for the improvement of the catalytic performance. The catalysts used in industrial processes and those of academic interest are described with emphasis on the mechanistic aspect. The catalysts include Pt supported on solid acids, sulfated zirconia, tungsten oxide supported on zirconia, oxycarbides of tungsten and molybdenum, and partially reduced MoO 3 . The mechanism of the isomerization over each catalytic system is described. The role of transition metals and hydrogen in bifunctional catalysts and the controversial mechanisms of alkane isomerization over sulfated zirconia are discussed in detail. Finally, recent development of the computational modeling and quantum mechanical calculations on alkanes activation and their transformations over zeolites are discussed with respect to the role of acid sites in the isomerization.

Mechanism of methanol conversion into hydrocarbons over ZSM-5 zeolite

The conversion of methanol into hydrocarbons over ZSM-5 zeolites has been investigated using a gas-recirculation system. The conversion proceeds autocatalytically. The reaction rate is greatly enhanced by the addition of ethylene or cis-but-2-ene, indicating that the autocatalysis is caused by the reaction of olefin and methanol. Infrared studies have revealed that methoxyl groups (—OCD3) are formed by the reaction of surface hydroxyl groups and methanol molecules (CD3OH), and they decompose to reproduce hydroxyl groups (—OD), giving hydrocarbons. The reaction mechanism in which methyl carbonium ions attack the C—H bond of methanol or dimethyl ether molecules is proposed. Methyl carbonium ions are supposed to be released from extensively polarised methoxyl groups formed by the reaction of methanol molecules and strong Bronsted-acid sites. In fact, strongly acidic materials, Nafion H and heteropolyacids, were found effective for methanol conversion. A semiquantitative analysis of the autocatalytic phenomenon in methanol conversion is also presented.

Selective conversion of methanol into aromatic hydrocarbons over silver-exchanged ZSM-5 zeolites

Abstract The introduction of Ag + ions into ZSM-5 zeolites appreciably enhances the selectivity for aromatic hydrocarbons in the conversion of methanol. Thus, the yield of aromatics over H-ZSM-5 and Ag-ZSM-5 was 43% and 80%, respectively, at 750 K. The distribution of aromatics over Ag-ZSM-5 at 750 K was 3, 12, 36 and 12% for benzene, toluene, xylenes plus ethylbenzene and C 10 +, respectively. It is concluded that Ag + ions have a capability of efficiently converting alkene intermediates into aromatic hydrocarbons.

Two-step synthesis of diphenyl carbonate from dimethyl carbonate and phenol using MoO3SiO2 catalysts

Abstract The transesterification of dimethyl carbonate with phenol to produce methyl phenyl carbonate was carried out in an autoclave using a variety of solid catalysts. MoO 3 SiO 2 was found to have a very high activity for this transesterification. Thus, a 17.1% yield of methyl phenyl carbonate based on phenol was obtained at 433 K in the presence of MoO 3 SiO 2 . MoO 3 SiO 2 was also an active catalyst for the disproportionation of methyl phenyl carbonate into diphenyl carbonate and dimethyl carbonate. A 48% yield of diphenyl carbonate was attained over MoO 3 SiO 2 at 443 K. These yield values are probably very close to those at the thermodynamic equilibrium.

Conversion of pentane into aromatics over ZSM—5 zeolites

Abstract The conversion of pentane into aromatic compounds over H-ZSM—5 and its Ga-exchanged form was studied. The selectivity to aromatics was greatly increased by Ga-loading and an aromatics yield of over 50% was attained at 550°C. The effect of contact time on the product distribution at 500°C was examined in detail in order to obtain information on the reaction pathway. At short contact times only the cracking of pentane prevails and, at extended contact times, olefins formed by the cracking are converted into aromatics. The Ga-loading does not affect the cracking ability of the zeolite, but enhances the activity for aromatization of olefins.