Hiro-o Tominaga

An infrared study of nitric oxide adsorbed on rhodium-alumina catalyst

Infrared spectroscopic study was made of NO and CO and their mixture adsorbed on rhodium metals supported on γ-alumina. When NO is adsorbed on rhodium, two surface species are identified: cationic one (M NO+) produced by donation of an electron antibonding (π2pz*) of NO to d orbital of the metal to strengthen the NO bond, and anionic one (M NO−) produced by transfer of a d electron of the metal to an antibonding π2pz* orbital of NO to weaken the NO bond. Cis-type coordination of NO and CO to one rhodium atom was found. When NO is first adsorbed and CO is introduced to react with the adsorbed NO, M NCO (isocyanate) is formed which is stable up to 400 °C under vacuum.

Synthesis gas conversion utilizing mixed catalyst composed of CO reducing catalyst and solid acid: II. Direct synthesis of aromatic hydrocarbons from synthesis gas

Abstract The synthesis of aromatic hydrocarbons from carbon monoxide and hydrogen was studied under pressurized conditions using hybrid catalysts composed of a methanol synthesis catalyst (Pd/SiO 2 ) and zeolites. Combination of Pd/SiO 2 with H-ZSM-5 or H-mordenite gave aromatic hydrocarbons with selectivities higher than 50%. Coupling of Pd/SiO 2 with H-Y gave little aromatics. Aromatic hydrocarbons formed on the H-ZSM-5 based catalyst, were mostly tetramethyl and pentamethyl benzenes, significantly different from those obtained by the reaction of methanol on the H-ZSM-5 alone. The yield of hydrocarbons was far higher than the level which is estimated from the thermodynamic equilibrium of methanol formation. The hydrocarbon formation was favored by the high reaction temperature and the high operating pressure. A reaction scheme of the hydrocarbon formation on the hybrid catalyst will be described which includes (i) formation of methanol, (ii) conversion of methanol to olefins, (iii) aromatization of olefins, (iv) hydrogenation of olefins on Pd/SiO 2 , and (v) methylation of aromatic hydrocarbons by methanol on zeolites.

Pyrolysis of chlorophyll a after preliminary heating at a moderate temperature: Implications for the origin of prist-1-ene on kerogen pyrolysis

Abstract Pyroprobe pyrolyses of chlorophyll a were performed to investigate the possible precursors and formation mechanisms of prist-1-ene often observed in the products of kerogen pyrolysis. Thermal maturation was simulated by preheating chlorophyll a for different times at 250°C. Phytadienes dominated the pyrolyzates from unheated or briefly preheated samples. Little prist-1-ene was produced from unheated chloropyll a during pyrolysis at 400°C for 1 s, whereas a considerable yield was obtained after preheating. Pyrolysis at 470°C for 15 s produced prist-1-ene from both unheated and preheated chlorophyll a. The yield of prist-1-ene increased with the time of preheating, relative to the yield of phytadienes. Additional isoprenoid hydrocarbons (C 9 C 20 ) were formed from the fragmentation of chlorophyll a. Possible pyrolysis mechanisms to explain these results are presented.

Synthesis gas conversion utilizing mixed catalyst composed of CO reducing catalyst and solid acid

The synthesis of aromatic hydrocarbons from carbon monoxide and hydrogen was studied under pressurized conditions using hybrid catalysts composed of a methanol synthesis catalyst (Pd/SiO/sub 2/) and zeolites. Combination of Pd/SiO/sub 2/ with H-ZSM-5 or H-mordenite gave aromatic hydrocarbons with selectivities higher than 50%. Coupling of Pd/SiO/sub 2/ with H-Y gave little aromatics. Aromatic hydrocarbons formed on the H-ZSM-5 based catalyst, were mostly tetramethyl and pentamethyl benzenes, significantly different from those obtained by the reaction of methanol on the H-ZSM-5 alone. The yield of hydrocarbons was far higher than the level which is estimated from the thermodynamic equilibrium of methanol formation. The hydrocarbon formation was favored by the high reaction temperature and the high operating pressure. A reaction scheme of the hydrocarbon formation on the hybrid catalyst will be described which includes: formation of methanol, conversion of methanol to olefins, aromatization of olefins, hydrogenation of olefins on Pd/SiO/sub 2/, and methylation of aromatic hydrocarbons by methanol on zeolites.

Supported molybdenum catalysts for alcohol synthesis from CO-H2

Abstract Mo catalysts supported on MgO, SiO 2 , Al 2 O 3 and TiO 2 were found to produce light alcohols from synthesis gas. Over the SiOO 2 -supported catalyst, the activity and selectivity for alcohol formation were greatly improved by addition of alkali metal salts. The alcohol formation activity, however, gradually decreased with processing time over Mo-K2 C O 3 /SiO 2 catalyst. On the other hand, addition of alkali metal halides to Mo/SiO 2 caused increases in the activity and selectivity for alcohols with processing time. Mo-KCl/SiO 2 catalyst had the highest activity for alcohol synthesis among all the catalysts studied. The alcohol formation activities of Cr- and W-KCl/SiO 2 catalysts have been studied. Over the Cr-based catalyst methanol was the main component of alcohols, while the W-based catalyst gave a high C2+/C1 alcohol ratio.

Mechanistic study on the alcohol synthesis over molybdenum catalysts: Addition of probe molecules to COH2

The addition of probe molecules, such as ethylene, propylene, methanol, ethanol, and acetaldehyde, to COH2 feed was studied over the KCl-promoted and the unpromoted MoSiO2 catalyst under synthetic conditions, in order to clarify the reaction paths for the formation of hydrocarbons and alcohols. The results of olefin addition study suggest that the alcohol formation from COH2 proceeds by a mechanism including steps identical with those in the hydrocarbonylation of olefins and that KCl suppresses the simple hydrogenation of olefins. Both of the Mo catalysts demonstrate a poor catalytic activity for the homologation of methanol to ethanol. Alcohol homologation seems to be only a minor process in the formation of C+2 alcohols. No significant activity of Mo catalysts for incorporation of acetaldehyde into C3 oxygenated compounds may exclude the intermediacy of aldehydes for the chain growth of alcohols. Hydrogenation of acetaldehyde to ethanol is the fast and predominant reaction, in agreement with the fact that alcohols compose more than 90% of the organic oxygenates produced from COH2. Aldol condensation is apparently unimportant for the chain growth. The contribution of alcohol dehydration to hydrocarbon formation may be insignificant over the KCl-promoted catalyst with KMo = 0.4. Consequently, a mechanism including CO insertion into the alkyl-metal bond is proposed for the main reaction path for the higher alcohol formation from COH2. The role of K is supposed to slow the hydrogenation of surface alkyl species to form alkanes as well as to increase the active sites for alcohol formation by retarding the reduction of Mo.

Vapor phase carbonylation of dimethyl ether and methyl acetate with nickel-active carbon catalysts

Abstract Vapor phase carbonylation of dimethyl ether and methyl acetate on nickel-active carbon catalysts was studied under pressurized conditions in the presence of methyl iodide as a promoter. Methyl acetate was synthesized from dimethyl ether and carbon monoxide with a selectivity of 80 to 90% at 250° C and 11 atm. A small amount of acetic anhydride was obtained at higher pressure which was essential for the acetic anhydride formation from methyl acetate. By-products such as acetic acid, methane and carbon dioxide were formed in both reactions. In particular, fairly large amount of acetic acid was formed in spite of the reaction under water free condition to bring about the decrease in the selectivity to acetic anhydride.

Shape selectivity as a function of pore size in epoxidation of alkenes with supported titanium catalysts

Reactant shape selectivity of supported titanium catalysts for epoxidation of cyclohexene and 2-hexene has an excellent correlation with the pore diameter of the catalysts. With titanosilicate the preference to cis isomer epoxidation is small compared to TiO2-SiO2 probably because of the restriction of its diffusion imposed by the zeolite micropore structure.

Selective oxidative coupling of methane over supported alkaline earth metal halide catalysts

Abstract Halides of alkaline earth metals supported on calcium oxide or magnesium oxide were found to be excellent catalysts for the oxidative coupling of methane. For example, the selectivity with respect to C 2 hydrocarbons over a 5 wt.-% MgCl 2 /CaO catalyst reached 90% or higher with a yield of 10% at 750°C and CH 4 /O 2 =9. Although the selectivity with respect to C 2+ hydrocarbons gradually decreased with processing time, the in situ replenishment of the trace amount of halogen compound in the feed gas prevented this decrease. The halide ion in the catalyst is inferred to change the surface character of the alkaline earth metal oxide, reducing its ability for methane decomposition and resulting in suppression of the deep oxidation of methane.

Importance of sequence of impregnation in the activity development of alkali-promoted mo catalysts for alcohol synthesis from COH2

The selective production of C/sub 2//sup +/ alcohols from CO and H/sub 2/ is of both commercial and academic interest in C/sub 1/ chemistry. The alcohol mixtures can be used as additives in gasoline to enhance the octane number. There are a number of reports on the catalysts for the synthesis of light alcohols. Synthesis of alcohols on molybdenum-based catalysts, however, was not reported until the authors discovery that mixed alcohols were efficiently produced from CO and H/sub 2/ on alkali-promoted molybdenum catalysts. Other interesting features of Mo catalysts were that they operated well in a CO-rich gas and are resistant to sulfur poisoning. In the initial study in this laboratory, catalysts were prepared by coimpregnation of SiO/sub 2/ with KCl and Mo salts. As the Mo loading was decreased, however, the authors encountered a difficulty in preparing the catalyst with good reproducibility. Hence they have employed different preparations for the Mo-K/SiO/sub 2/ catalysts. In this note they report that sequence of impregnation greatly affects the activity and selectivity. A sequence in which the K is added first, followed by impregnation with (NH/sub 4/)/sub 6/Mo/sub 7/O/sub 24/, gives rise to reproducible preparation of catalysts for alcohol production. 26 references.