Kimio Kunimori

Catalytic performance and properties of ceria based catalysts for cyclic carbonate synthesis from glycol and carbon dioxide

Ceria based catalysts are very effective for the synthesis of cyclic carbonate such as ethylene carbonate (EC) and propylene carbonate (PC) by the reaction of CO2 with ethylene glycol and propylene glycol. In these reactions, polycarbonate and ethers (diethylene glycol and dipropylene glycol) were not detected under optimum reaction conditions. This indicates that the PC and EC formation over CeO2–ZrO2 catalysts is highly selective. Catalytic activity was much dependent on the composition and calcination temperature of catalysts. On the basis of catalyst characterization by means of surface area measurement, X-ray diffraction, thermogravimetric analysis, and temperature programmed desorption of NH3 and CO2, the relations between catalytic performance and properties are discussed.

Catalyst development for the gasification of biomass in the dual-bed gasifier

Abstract A dual-bed gasifier system combined with catalysts was evaluated in the catalytic gasification of cedar wood at low temperatures (823–973xa0K). The dual-bed gasifier consisted of a primary-bed section for pyrolysis of biomass and separation of pyrolyzed gas and tar from solid products and a secondary-catalytic tar reformer. Catalyst development was carried out on the basis of Rh/CeO 2 /SiO 2 , which has been developed for the higher conversion of carbon to gas and higher yield of CO+H 2 +CH 4 . We have also carried out the optimization of reaction conditions. Especially, the tar derived from maximum of 250xa0mg biomass/min can be totally converted to the gas product by 3xa0g catalyst in this system using ER=0.25 of total carbon present in the biomass. This performance was much higher than that over commercial steam reforming catalyst. In addition, the amount of coke deposited on Rh/CeO 2 /SiO 2 was much smaller. In the dual-bed system combined with excellent catalysts, almost all the tar can be converted to syngas at lower temperature than that needed by the conventional method with high energy efficiency.

Shape-selective isopropylation of biphenyl over H-mordenites: Relationships of bulk products and encapsulated products in the pores

Abstract Shape-selective formation of 4,4′-diisopropylbiphenyl (4,4′-DIPB) was observed in the isopropylation of biphenyl (BP) over H-mordenite (HM). Shape-selectivity was governed by spatial restriction in transition states in the microporous environment of HM. The selectivity for 4,4′-DIPB was influenced by many factors such as the SiO2/Al2O3 ratio, reaction temperature, and propylene pressure. On the other hand, high selectivities for 4,4′-DIPB were observed in encapsulated products under all of our conditions because of shape-selective catalysis in the HM pores. However, the decrease in the selectivity for 4,4′-DIPB occurred with the decrease in the SiO2/Al2O3 ratio and with change in the reaction conditions, such as increase in temperature and decrease in propylene pressure. The discrepancies in bulk products and in encapsulated products in the HM pores are discussed to understand where and why shape-selective catalysis occurs. The decrease in the selectivity for 4,4′-DIPB over HM with a low SiO2/Al2O3 ratio is due to non-regioselective reactions because of choking of the pore entrance by coke-deposition. The decrease in the selectivity for 4,4′-DIPB under high reaction temperatures, or under low propylene pressures was ascribed to the isomerization of 4,4′-DIPB at external acid sites. These conclusions are also supported by discrepancies of bulk and encapsulated products in the isomerization of 4,4′-DIPB under high the corresponding conditions. No significant isopropylation of 4,4′-DIPB to triisopropylbiphenyls (TrIPB) was observed even under high propylene pressure or at high reaction temperatures. This is presumably due to there not being enough space in the pores for the transition state of further isopropylation of 4,4′-DIPB, and it is one of the reasons for the shape-selective formation of 4,4′-DIPB.

Catalyst performance in reforming of tar derived from biomass over noble metal catalysts

An activity test in the reforming of tar derived from cedar biomass over M–CeO2–SiO2 n(M = Rh, Pt, Pd, Ru, Ni) was carried out in a secondary fluidized catalyst bed at lower temperature range (823–923 K) than the conventional methods. We have measured the formation rate of CO, CO2, CH4, H2, and the yield of coke deposited on the catalyst surface and the yield of char accumulated in the primary bed. It was found that Rh–CeO2–SiO2 exhibited much higher performance than other metal catalysts in terms of the activity of tar reforming, and the yield of gas and coke.

Catalytic properties of Rh/CeO2/SiO2 for synthesis gas production from biomass by catalytic partial oxidation of tar

Abstract Performance of Rh/CeO2/SiO2 in the partial oxidation of tar from the pyrolysis of wood biomass (architectural salvage) was investigated and compared with various materials such as steam reforming Ni catalyst, active clay, USY zeolite, MS-13X, dolomite, alumina, silica sand, fluorite and non-catalyst. Rh/CeO2/SiO2 and the steam reforming Ni catalyst exhibited much higher performance than any other materials in terms of hydrogen production and the amount of tar. Therefore, the performance of Rh/CeO2/SiO2 and steam reforming Ni catalyst was particularly compared. From the result on the dependence of reaction temperature, equivalence ratio, and biomass feeding rate, Rh/CeO2/SiO2 exhibited higher performance than the Ni catalyst, especially in terms of tar and coke amount. Furthermore, Rh/CeO2/SiO2 was also more stable than the Ni catalyst. The catalyst deactivation can be related to the amount of coke deposition. The results indicate that Rh/CeO2/SiO2 has high resistance to coke formation, and this is related to higher combustion activity of Rh/CeO2/SiO2 than the Ni catalyst.Furthermore, from the TPR profiles, Rh/CeO2/SiO2 had higher reducibility than the Ni catalyst. The combination of high combustion activity with high reducibility and reforming activity can be related to high performance of tar conversion in the fluidized bed reactor.

Steam reforming of methanol over Pt–Zn alloy catalyst supported on carbon black

Abstract Steam reforming of methanol over Zn-promoted Pt catalyst supported on an electrically conductive carbon black has been investigated after H2 reduction at 873 K. X-ray diffraction measurement showed that Pt–Zn alloy was formed on the carbon black (C). The Zn-promoted Pt/C catalyst showed higher activity and selectivity to CO2 compared with unpromoted Pt/C catalyst. Methyl formate was formed over the Zn-promoted Pt/C catalyst in decomposition of methanol (without water). This suggests that steam reforming of methanol over the Zn-promoted Pt/C catalyst can proceed via methyl formate, which is different from that of the unpromoted Pt/C catalyst.

NMR study of pore surface and size in the mesoporous material FSM-16

Abstract The surface structure, pore size distribution and pore wall thickness of the mesoporous material FSM-16 have been studied by X-ray powder diffraction (XRD), 1 H and 29 Si MAS NMR and 1 H liquid-state NMR, and by applying surface silylation as a probe. The concentrations of surface hydroxyl groups for FSM-16 are estimated from 29 Si MAS NMR, and amount to 3×10 21 g −1 , corresponding to approximately 3 nm −2 . O 2 molecules contribute to 29 Si spin–lattice relaxation of Q 2 and Q 3 as well as Q 4 , suggesting thin walls. 1 H-MAS-NMR spectra indicate the presence of isolated and hydrogen-bonded hydroxyl groups. Both hydroxyl groups are silylated, and the silylated fraction is about 50%. The spatial distribution of surface hydroxyl groups is estimated from the line width in 1 H static spectra. A rather homogeneous distribution is demonstrated in one of the samples. The sample with a less homogeneous distribution has a larger affinity for moisture. The pore size and pore wall thickness were determined by 1 H NMR measurements on water-saturated FSM-16 samples, and the results are in good agreement with literature values obtained by N 2 adsorption isotherms and transmission electron micrographs on a similar sample. In benzene-saturated samples, a non-freezing surface layer of benzene is much thicker than that of water which indicates a stronger interaction between benzene and the FSM-16 surface.

Dynamics of benzene, cyclohexane and n-hexane in KL zeolite studied by 2H NMR

Molecular motions of benzene-d6, cyclohexane-d12 and n-hexane-d14 sorbed at loading levels of 1 molecule per channel lobe in KL zeolite have been studied by 2H NMR. The spectra were recorded in the temperature range from 124 to 373 K, and they were successfully simulated. At low temperatures, benzene molecules rotate fast around the C6 axis, and cyclohexane molecules rotate fast around the C3 axis of the chair form, where the directions of the rotation axis are fixed. With increase in temperature, benzene, cyclohexane, and n-hexane molecules start jumping among the six equivalent sites on K+ ions. Further increases in temperature results in the increase in the fraction of molecules located at the central space of the micropore which undergo isotropic motions and exchange with the molecules on the K+ ions. The mean residence time on the K+ ion is in the following order: benzene-d6>cyclohexane-d12>n-hexane-d14. The apparent activation energies derived from the mean residence times are 28.0±1.6 kJ mol-1 (220 K⩽T⩽373 K) for benzene-d6, 9.6±1.2 kJ mol-1 (160 K⩽T⩽260 K) and 44.3±3.6 kJ mol-1 (280 K⩽T⩽373 K) for cyclohexane-d12, and about 10 kJ mol-1 for n-hexane-d14. The large activation energy at the high temperatures in cyclohexane-d12 might be caused by the conformation inversion of the cyclohexane ring. The ratios of the numbers of molecules in the central space to those on the K+ ions are in the order of benzene-d6 cyclohexane-d12>n-hexane-d14.

Isotopic study of nitrous oxide decomposition on an oxidized Rh catalyst: mechanism of oxygen desorption

N2O decomposition on an oxidized Rh catalyst (unsupported) has been studied using a tracer technique in order to reveal the reaction mechanism. N216O was pulsed onto an 18O/oxidized Rh catalyst at 493 K and desorbed O2 molecules were monitored. The 18O fraction in the desorbed oxygen had the same value as that on the surface oxygen. The result shows that the oxygen molecules do not desorb via the Eley–Rideal mechanism, but via the Langmuir–Hinshelwood mechanism. On the other hand, desorption of oxygen from Rh surfaces (in vacuum or in He) occurs at higher temperatures, which suggests reaction-assisted desorption of oxygen during the N2O decomposition reaction at low temperature.