KAGAKU KOGAKU RONBUNSHU
Online ISSN : 1349-9203
Print ISSN : 0386-216X
ISSN-L : 0386-216X
Volume 21 , Issue 6
Showing 1-30 articles out of 30 articles from the selected issue
  • Takeshige Takahashi, Takami Kai
    1995 Volume 21 Issue 6 Pages 961-971
    Published: December 10, 1995
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    Hydrogenation of benzene and carbon dioxide was carried out over catalysts prepared from amorphous alloys containing zirconium. The hydrogenation activity of the alloys was very low in the virgin state, but the activity gradually increased in the order of oxidation, reduction in a hydrogen atmosphere and hydrogenation. Characterization of the amorphous alloys revealed that the increase in surface area caused by oxidation of zirconium was responsible for the increase in catalytic activity. When the alloys were oxidized in an oxygen atmosphere, the active metal atoms for hydrogenation and zirconium in the alloys were simultaneously oxidized. When the oxidized alloys were treated in a hydrogen atmosphere, palladium, platinum and nickel oxides were reduced to the respecture metal atoms, whereas zirconium oxide remained. As a result, palladium, platinum or nickel catalysts supported on zirconium oxide were prepared from the amorphous alloys.
    The principal advantage of a catalyst prepared from an amorphous alloy was high dispersion of active metal on the surface, despite the high content of metal.
    Amorphous alloys containing zirconium are considered to be an attractive catalyst precursor for hydrogenation.
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  • Kazuo Idei, Yasuo Yamamoto, Hatsutaro Yamazaki
    1995 Volume 21 Issue 6 Pages 972-983
    Published: December 10, 1995
    Released: November 12, 2009
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    Catalyst deactivation in hydrodesulfurization (HDS) of petroleum distillates is caused by coking alone but deactivation in HDS of residue is due to a combination of coking and the deposition of metals, such as Ni and V. The objective of the present study is to determine the HDS activity of commercial catalysts affected by coke, metals and so on.
    According to a long term test for catalyst deactivation using light gas oil, vacuum gas oil and atmospheric residue, we proposed a kinetic model of simple simultaneous equations that supposed the mechanism of catalyst deactivation as a first-order reduction of different active sites in HDS of light and heavy oils. We hypothesized that the deactivating species are composed of two types : one that loses activity easily and the other that does not and derived an analysis method. This deactivation equation could successfully express the deactivation behaviors in extensive HDS, and was confirmed to be applicable to the various catalyst deactivations of light and heavy oils.
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  • Yasukazu Saito, Hideaki Ogino, Tomoyuki Fukushima
    1995 Volume 21 Issue 6 Pages 984-989
    Published: December 10, 1995
    Released: November 12, 2009
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    Carbon-supported Pt-Ru composite catalysts that were dehydrogenation-active for alcohol under boiling conditions were prepared from the mixed chlorides RuCl3 and K2PtCl4, and from complexes with different charges [Pt3 (CO) 6] 2-4and [(C6Me6) 2Ru] 2+. The former gave broad particle-size distributions. A definite relationship between size and composition was elucidated by EDX analysis, namely that Ru-rich particles were small but Pt rich particles were large. As far as 2-propanol dehydrogenation was concerned, however, the most important factor for catalysis was the Pt/Ru ratio as a whole.
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  • Masahiro Kishida, Kazuyuki Umakoshi, Kim Won Young, Toshiaki Hanaoka, ...
    1995 Volume 21 Issue 6 Pages 990-996
    Published: December 10, 1995
    Released: November 12, 2009
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    This paper describes a novel preparation method using microemulsion for supported metal catalysts. In this study, the preparation of silica-supported rhodium catalysts was investigated mainly in the polyethylene (5) glycol-p-nonylphenyl ether/cyclohexane system. The catalysts prepared by this method had a smaller average particle size with an appreciable narrow size distribution and exhibited a much higher activity for the hydrogenation of carbon monoxide than a catalyst prepared by the impregnation method. Control of the metal particle size was also investigated for the silica-supported rhodium catalyst, and the particle size was found to be controlled by adjusting the water-to-surfactant molar ratio, the concentration of RhCl3 in microemulsion, and the type microemulsion system.
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  • Toshihiro Nakai, Emiko Sumida, Hidenori Yahiro, Masaru Shiotani, Kazuo ...
    1995 Volume 21 Issue 6 Pages 997-1001
    Published: December 10, 1995
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    Liquid phase oxidation of benzene to phenol was studied using palladium / silica catalysts prepared by impregnation and ion-exchange methods. The catalyst prepared by impregnation showed high catalytic activity, but the catalyst prepared by ion-exchange showed no catalyst activity. The high catalytic performance of the former was ascribed to the presence of Cl- ions on the catalyst surface. The reaction of benzene with hydrogen peroxide revealed that hydroxyl radical produced by the decomposition of hydrogen peroxide was an intermediate in the oxidation of benzene, and that Cl- ion suppressed a side reaction between hydrogen peroxide and hydrogen supplied on the catalyst.
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  • Choji Fukuhara, Shinobu Sekiguchi, Hideaki Muto, Akira Igarashi
    1995 Volume 21 Issue 6 Pages 1002-1008
    Published: December 10, 1995
    Released: November 12, 2009
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    Decomposition of methanol has been studied over various noble metal and copper catalysts at temperatures from 300 to 450°C. Screening experiments showed that Rh, Pd, and Pt catalysts supported on ZrO2 had high activities and high selectivities for carbon monoxide and hydrogen. The Pd/ZrO2 catalyst was not deactivated with time on line.
    From a kinetic study, it was found that the partial pressure dependency of the initial reaction rate on the Pd/ZrO2 catalyst was zero-th order with respect to methanol. This means that a methanol molecule is strongly adsorbed on the catalyst surface and the rate determining step involves the removal of hydrogen from an adsorbed methoxy group.
    Further, the decomposition rate over the Pd/ZrO2 catalyst was increased by hydrogen and decreased by carbon monoxide.
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  • Osamu Suwata, Yasuo Ikeda, Tomohiro Fujimatsu, Yasuaki Okamoto, Yuriko ...
    1995 Volume 21 Issue 6 Pages 1009-1014
    Published: December 10, 1995
    Released: November 12, 2009
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    The effects of the preparation method on the catalytic properties of Cu-ZrO2 catalysts were studied for the synthesis of methanol from CO2 and H2. The preparation parameters, namely composition, coprecipitation temperature, salt/Na2CO3 mole ratio and starting salt, were examined in detail. Cu-ZrO2 catalyst (50%Cu) prepared by using copper chloride and zirconium sulfate showed a remarkably higher activity than Cu-ZrO2 catalysts prepared by other combinations of starting salts; chloride, nitrate and sulfate. The high activity of the Cu-ZrO2 catalyst can be explained in terms of the formation of relatively large crystalline copper metal with edge or corner sites decorated with chloride ion and in terms of highly dispersed zirconium species.
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  • Toshihiro Miyao, Masakuni Matsuoka, Isao Shishikura, Masatoshi Nagai
    1995 Volume 21 Issue 6 Pages 1015-1023
    Published: December 10, 1995
    Released: November 12, 2009
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    Aluminum-supported Molybdenum carbide was prepared using a vertical tube hot-wall CVD reactor at a temperature of 500°C800°C and 0.070.21 kPa total pressure. Amorphous molybdenum carbide was formed on a quartz plate in the range of 500°C-700°C, and Mo3C2 crystals were formed above 700°C. Conformal step cover-age on micro-trenches was obtained at a pressure of 0.07 kPa. The hydrogenation of CO2 was carried out at a reaction temperature of 400°C and 0.1 MPa total pressure. The main reaction products were CO and H2O and the selectivity to CO was above 99%. CVD carbide catalysts were 3 and 15 times more active per molybdenum loading than impregnated carburized and reduced catalysts, respectively.
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  • Xiao Hong Li, Keiichi Tomishige, Kaoru Fujimoto
    1995 Volume 21 Issue 6 Pages 1024-1031
    Published: December 10, 1995
    Released: November 12, 2009
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    We discovered that oxygen species adsorbed on SrTi1-xMgxO3-δ catalysts prepared by the addition of Mg2+ ions instead of Ti4+ ions on an SrTiO3 catalyst reacted with methane to form ethane selectively at temperatures as low as 700 K. At this temperature the catalytic reaction did not proceeded under atmospheric pressure because the oxygen adsorption site was poisoned by H2O which was a reaction product. We found that highly selective and catalytic C2 hydrocarbons were formed on these catalysts by CH4-H2O and CH4-CO2 reactions similar to a CH4-O2 reaction.
    It is suggested that H2O and CO2 were effective oxidants for the oxidative coupling of methane. In the cases of CH4-O2 and CH4-H2O reactions, SrTi0.4Mg0.6O 3-δ showed superior catalytic performance compared to SrTiO3 whereas the reverse was tone for a CH4-CO2 reaction. The interaction between oxidizing reagents and oxide ion defects seems to play an important role in the catalytic activity and selectivity of the oxidative coupling of methane.
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  • Yasutake Teraoka, Yoshiaki Taura, Isamu Moriguchi, Shuichi Kagawa
    1995 Volume 21 Issue 6 Pages 1032-1038
    Published: December 10, 1995
    Released: November 12, 2009
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    Perovskite-type La0.8Sr0.2MO3 (M =Co, Mn) compounds were prepared by malic acid-aided (MAL) and reverse homogeneous precipitation (RHP) methods and their catalytic activities for the total oxidation of methane were examined. Monophasic perovskites could be prepared by both methods at 823 K, which was lower by 300 K than the conventional nitrate decomposition (NIT) method. The lowering of the calcination temperature resulted in an increase in specific surface area. It appears that precursors with homogeneously dispersed constituent metal cations are formed by complexing metal cations with malic acid in the MAL method or by rapid and homogeneous precipitation as metal hydroxides in the RHP method, and therefore the formation of the perovskite phase at lower temperatures is facilitated. High surface-area oxides prepared by the MAL and RHP methods showed higher catalytic activity for methane oxidation than oxides prepared by the NIT method, though promotion of weight-normalized activity by the increased surface area was more prominent in La0.8Sr0.2MnO3 than in La0.8Sr0.2CoO3. These results clearly indicate that MAL and RHP methods are very useful for preparing highly active perovskite catalysts.
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  • Toshiyuki Yokota, Hiroto Ohwada
    1995 Volume 21 Issue 6 Pages 1039-1046
    Published: December 10, 1995
    Released: November 12, 2009
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    Semiconductor photocatalysts of TiO2/SiO2 composite particles were prepared by hydrolysis of titanium isopropoxide. The hydrolysis was performed in an ethyl alcohol solution in which spherical silica particles of micron order dimensions were supplied as a substrate for TiO2 deposion. A sub-micron meters TiO2 layer was observed on the particle surface. These TiO2-coated silica particles were heat treated to form an anatase or a rutile crystal phase of TiO2. The photo-electrochemical deposition method was adopted to generate platinum metal dots on the TiO2. surface. The photocatalytic activity of the particles was assessed by photo-decomposition of methyl alcohol in aqueous solution. The results of decomposition showed that anatase type TiO2 of 0.25 μm thickness containing 0.75 wt% of deposited platinum exhibited sufficient activity. Separation of the suspended catalyst particles was easily achieved by simple filtration after the reaction. Therefore, this catalyst may be suitable for practical usage in large scale industrial operations.
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  • Taki Matsumoto, Yasushi Murakami, Kiyochika Yahikozawa, Yoshio Takasu
    1995 Volume 21 Issue 6 Pages 1047-1053
    Published: December 10, 1995
    Released: November 12, 2009
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    The sol-gel process for tin tetra-n-butoxide in butanol was analyzed by viscosity measurements. Precipitation of tin oxide-containing ultrafine particles was observed without a viscosity increase in the absence of diethylene glycol. On the other hand, the viscosity increased by the addition of diethylene glycol without any precipitation. The induction period and the slope of the rise in the viscosity after the induction period were independent of the diethylene glycol content, but they depended remarkably upon the water content. Monte Carlo simulation was carried out on the basis of the reaction model consisting of forward and reverse reactions of hydrolysis and polycondensation of tin tetra-n-butoxide with the molecular size effect. The simulation results were consistent with data on the viscosity measurements.
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  • Tomohiro Nakayama, Satoshi Sato, Toshiaki Sodesawa, Fumio Nozaki
    1995 Volume 21 Issue 6 Pages 1054-1059
    Published: December 10, 1995
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    In order to obtain metal oxides having high specific surface areas for catalysts, preparation of metal oxides by using organic acids was investigated. Metal oxides such as MgO, La2O3, CeO, and NiO were prepared by heat treatment of precursors which had been obtained by melting a mixture of respective metal salts and organic acids at 343K. Hydroxycarboxyllic acids such as citric acid and lactic acid, as well as amino acids such as glycine, were effective in producing materials which had high specific surface areas. For example, the specific surface areas of the magnesia prepared by using hydroxicarboxyllic acids were higher than those prepared by the precipitation method. Compared with MgO prepared by pyrolysis of magnesium nitrate, SEM observation and pore size distribution indicate that MgO prepared by this method has a characterstic shape and mesopores formed by elimination of organic acids.
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  • Eiji Sasaoka, Shoji Kaneshima, Yusaku Sakata, Tadao Nakatsuji, Shigeak ...
    1995 Volume 21 Issue 6 Pages 1060-1068
    Published: December 10, 1995
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    To clarify the effect of the preparation conditions of Mn2O3 catalysts on their activity for the decomposition of ozone, Mn2O3 catalysts were prepared from manganese salts [Mn (NO3) 2, MnCl2, MnSO4] using alkali (NaOH, KOH, Na2CO3, NH3) and ozone (O3-O2 mixed gas) under different conditions. Catalytic activities (conversion of O3 to O2) of the prepared samples were measured using a fixed-bed flow type reactor.The inlet gas was mainly composed of O3 (235 ppm), O2 (18.2%), H2O (2.35%) and N2 (balance). The rate of catalytic decomposition was analyzed as a first order reaction with regard to O3 concentration, and the rate constant, k thus obtained was used to evaluate the surface activity. The total surface area of the sample charged in the reactor (Sv) was calculated from the specific surface area and weight of the sample, and used for evaluation of the effect of surface area on catalytic activity.
    By evaluating k and Sv, the effects of preparation conditions on the activity of the sample were clarified. Furthermore, differences between alkali precipitation and ozone precipitation methods were also clarified. From this study, it was concluded that an active catalyst for ozone decomposition could be prepared by the ozone precipitation method as well as by the alkali precipitation method.
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  • Satoshi Terai, Kyu Murata, Kyoko Yamamoto, Hideo Kameyama
    1995 Volume 21 Issue 6 Pages 1069-1074
    Published: December 10, 1995
    Released: November 12, 2009
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    Preparation of a plate-type catalyst by anodization and sealing treatment has been proposed. Commercial aluminum plate was anodized in 4wt% oxalic acid solution at 20°C. An alumina layer was formed on the plate surface. Meso-pores ranging from 20 to 30 nm in radius were formed in the anodized alumina film by changing the current density of anodization.
    After the anodization, the pores were enlarged to 40nm in radius by soaking the plate in oxalic acid solution. These pores could be sealed by hydration. The temperature and treatment time of hydration were controlled and the pores were sealed to 2-40 nm in radius and showed double peaks in their pore size distribution.
    The alumina on aluminum plates was used for support of catalysts. These supports differing in pore size distribution were impregnated with platinum. The impregnation was done (a) concurrently with hydration by chloroplatinic acid aqueous solution, or (b) using sodium silicate-acetone solution of chloroplatinic acid. The physical properties of three catalysts prepared by these methods were determined and compared.
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  • Eiko Obuchi, Koji Yamamoto, Katsuyuki Nakano
    1995 Volume 21 Issue 6 Pages 1075-1081
    Published: December 10, 1995
    Released: November 12, 2009
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    Amorphous titania, obtained by hydrolysis and polymerization reactions of titanium tetra iso-propoxide, was dissolved in 31 % hydrogen peroxide solution to form a transparent gel. The gel was peptized by further addition of hydrogen peroxide solution, and then the transparent coating solution was obtained. Glass and stainless steel plates were dip-coated by this coating solution, dried in a clean bench, and calcined at 373-773 K for glass and at 373-973 K for stainless steel.
    The thin films calcined at 573-773 K were identified to be anatase by XRD and IR spectroscopies. The film calcined at 773 K was stable in 10 N hydrochloric and sulfuric acid solutions for one week. Photocatalytic activity was also tested with this film coated on glass plate. Dinitrophenol contained in a test solution was degraded under the irradiation from a sterilization Hg lamp.
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  • Kaoru Onoe, Ryoichi Yajima, Sinichi Suzuki, Tatsuaki Yamaguchi, Yuzuru ...
    1995 Volume 21 Issue 6 Pages 1082-1085
    Published: December 10, 1995
    Released: November 12, 2009
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    Perovskite-type LaFeO3 fine particles, prepared by a sol-gel method from an aqueous solution of nitrates, were dispersed in a dilute solution of water glass. The LaFeO3 catalyst was obtained by drying the suspension. The rate of LaFeO3 crystallite growth during thermal treatment was measured, and it was found that the fine particles suspended by water glass showed a highly inhabitory action against the crystallite growth of face (121).
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  • Jun Murata, Choji Fukuhara, Akira Igarashi
    1995 Volume 21 Issue 6 Pages 1086-1089
    Published: December 10, 1995
    Released: November 12, 2009
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    Steam reforming of methanol has been studied over plate-type copper catalysts. The copper catalysts on aluminum plate were prepared by electroless plating, i. e., the deposition of copper by chemical reduction.These plated Cu/Al catalysts showed low activity and high selectivity to carbon dioxide. The Cu-Ni/Al catalyst with nickel plated first showed high activity and high selectivity to carbon monoxide. Addition of zinc oxide to the Cu-Ni/Al catalyst resulted in an increase of formation of carbon dioxide with high activity.
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  • Tatsuya Nobusawa, Yoshinori Takagi, Toshihide Suzuki
    1995 Volume 21 Issue 6 Pages 1090-1095
    Published: December 10, 1995
    Released: November 12, 2009
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    Isomeriation of 1-methylnaphthalene has been carried out over various solid acid catalysts. A prolonged catalytic life was obtained by employing highly dealuminated HY zeolite as catalyst and methyltetralin (MT) as an additive to the feedstock. The optimum lifetime was obtained by HY zeolite whose unit cell constant was regulated between 24.30Å and 24.34Å Dealumination causes lower acid site density at the catalyst surface which inhibits the formation of heavier coke. The effect of MT can be attributed to its hydrogen donating properties. A higher selectivity to isomerization can be obtained in the presence of MT. Furthermore, diluent gas consumption can be minimized without shortening the catalytic life in the presence of MT. All other catalysts or additives had insufficient lifetime because of rapid formation of coke. In a long run test of isomerization, more than 6000 h of catalytic life was confirmed using the optimum catalyst and conditions.
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  • Yoshinori Takagi, Tatsuya Nobusawa, Toshihide Suzuki
    1995 Volume 21 Issue 6 Pages 1096-1103
    Published: December 10, 1995
    Released: November 12, 2009
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    We have developed methods of preventing catalytic deactivation on isomerization of 1-methylnaphthalene over HY-zeolite, by eliminating part of the aluminum from zeolite and adding a small amount of methyltetralin to the starting material. As a result of analysis of the coking behavior, a quantitative estimation method of catalytic life, which is necessary for the design of the catalyst, specification and reaction conditions, has been obtained. Because it was found that specific activity of the catalyst depended on the extent of coke deposition, accelerating the rate of coking by rasing the concentration of methylnaphthalene in the feed gas was effective for exact and rapid estimation. Consequently, it has been predicted that the desired yield of 2-methylnaphthalene, 60%, is maintained for one year or more, when HY-zeolite with a 24.32Å unit cell constant is used and 2-3% of methyltetralin is added to starting the 1-methylnaphthalene.
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  • Yasuo Miyake, Naoya Nakanishi, Toshikazu Nakajima, Yasuhiko Itoh, Tosh ...
    1995 Volume 21 Issue 6 Pages 1104-1109
    Published: December 10, 1995
    Released: November 12, 2009
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    Degradation phenomena of a reforming catalyst in a direct internal reforming molten carbonate fuel cell (DIR-MCFC), which holds promise for the highest efficiency among several types of fuel cells, were investigated. The initial performance of the DIR-MCFC was the same as that of an external reforming molten carbonate fuel cell (ER-MCFC), but the degradation rate of cell performance was greater than that of an ER-MCFC. It was found that catalyst deactivation due to electrolyte poisoning was the main reason for the high degradation rate. Electrolyte poisoning mainly occurred at the fuel gas inlet through liquid phase poisoning. Ni plating on the Inconel 600 corrugated current collector in the anode gas channel was tested in order to prevent electrolyte poisoning. It was found that Ni plating was effective to improve DIR-MCFC life characteristics by its contact angle to the molten carbonate electrolyte.
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  • Takao Kaneko, Yoichi Kageyama, Toshio Masunaga
    1995 Volume 21 Issue 6 Pages 1110-1119
    Published: December 10, 1995
    Released: November 12, 2009
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    Effects of preasphaltene and ash content on catalyst deactivation were investigated with a Ca-Ni-Mo/Al2O3 developed for secondary hydrogenation in two-stage brown coal liquefaction. Compared with Ni-Mo/Al2O3, little catalyst deactivation was observed with Ca-Ni-Mo/Al2O3 owing to a small carbonaceous deposit, even in the case of including large amounts of preaspaltenes, while a significant decrease in catalytic activity was observed with an increase in the ash content.
    It appeared that Na and K in ash having a small particle size could easily penetrate into the catalyst pore, resulting in poisoning of active sites. A remarkable change in surface area or pore structure was observed on the used catalyst collected from the inlet of a fixed bed reactor.
    It was found that the possibility of pore blockage by metal deposition may be ruled out, as the reduction in pore volume was mainly caused by carbonaceous deposition. These results suggest that initial deposition of carbonaceous materials and alkaline metals (Na, K) on the catalyst could cause catalyst deactivation in the initial stage.
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  • Atsushi Satsuma, Toshiyasu Ishikura, Takeshi Shimizu, Miki Niwa, Tadas ...
    1995 Volume 21 Issue 6 Pages 1120-1126
    Published: December 10, 1995
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    By using dealuminated and Ba-ion exchanged mordenites, the effect of the number and strength of acid sites on the rate of deactivation in methanol conversion has been examined. Although H-mordenite with a SiO2/Al2O3 ratio of 15 was seriously deactivated by deposition of coke, a decrease in the rate of deactivation was observed on dealuminated mordenites with a SiO2/Al2O3 ratio of more than 164 and on doubly modified mordenites. From NH3-TPD spectra, the number of strong acid sites in these modified mordenites was less than 0.5 per unit cell. Since an average distance between neighboring strong acid sites, calculated from this acid amount, is longer than the molecular diameter of polyalkylbenzene, it was supposed that suppression of deactivation is due to the reduction of adjacent strong acid sites for polymerization of polyalkylbenzenes.
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  • Takeshige Takahashi, Takuya Kodama, Takami Kai
    1995 Volume 21 Issue 6 Pages 1127-1132
    Published: December 10, 1995
    Released: November 12, 2009
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    The reaction of p-chlorotoluene over HY, H-mordenite and HZSM-5 zeolites was carried out in a fixed-bed type flow reactor to elucidate the effect of catalyst deactivation on the selectivity of the product. The main products of the reaction were chlorobenzene and m-chlorotoluene over HY and HZSM-5 zeolite, respectively. The difference in the coke production rates between the zeolites was responsible for the selectivity difference. The catalytic activity and m-chlorotoluene selectivity for the reaction over HZSM-5 zeolite decreased with process time, despite the low coke formation rate. The reduction of micropore size by coke deposition on the HZSM-5 zeolite caused a decrease in the catalytic acitivity and m-chlorotoluene selectivity. This interpretation was supported by the reaction of o-chlorotoluene over the same zeolite.
    The catalytic activity and the surface area of the spent zeolites decreased with process time due to catalyst deactivation. The deactivation coefficient of HZSM-5 calculated from the relationship between rate constant and process time decreased with reaction temperature. These results suggest that the selectivity for PCT reaction was dependent on the kind of zeolite.
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  • Takao Masuda, Shin Robert Mukai, Takashi Akiyama, Yoshihiro Fujikata, ...
    1995 Volume 21 Issue 6 Pages 1133-1139
    Published: December 10, 1995
    Released: November 12, 2009
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    A model has been developed to represent the deactivation of REY zeolite caused by coke deposition during catalytic cracking of heavy oil obtained from pyrolysis of waste plastics. Coke deposition not only leads to coverage of the acid sites, which contribute to the reaction, but also leads to a decrease in the intracrystalline diffusivity of the zeolite due to the reduction in effective pore opening, resulting in deactivation of the catalyst. In this work, firstly the amount of strong acid sites and the diffusivity of catalysts with different amounts of coke loading were measured, and empirical equations, which represent the relationships between the amount of coke loading and these two values, were obtained. Finally, a model was developed to calculate the transient change of the catalyst activity and the concentration distributions of the components within the reactor by employing the obtained empirical equations. The calculated results agreed well with experimental results. Using this model, it was found that the deactivation rate of the catalyst was reduced under diffusion control conditions, and large catalyst particles could maintain their activity longer than small catalyst particles.
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  • Hideo Yamano, Yasunori Oumi, Momoji Kubo, Rajappan Vetrivel, Akira Miy ...
    1995 Volume 21 Issue 6 Pages 1140-1146
    Published: December 10, 1995
    Released: November 12, 2009
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    The thermal destruction process of AlPO4-5 and VPI-5 was investigated by using molecular dynamics and computer graphic methods. The mobility of atoms in AlPO4-5 was increased and the framework became unstable as the temperature increased. Finally the framework transformed into an amorphous phase. During this process, bonds between Al and O were frequently broken or formed, P-O bonds were, however, scarcely changed. This indicates that the Al-O bond in the framework is weaker than the P-O bond. AlPO4-5 has only one T (T = Al or P) site, whereas three crystallographically distinct T sites are located in VPI-5. Thus, we also investigated dynamic differences between Al atoms located in distinct T sites during the thermal destruction process of VPI-5. It was found that Al-O bonds formed by Al atoms at the T 1 site are most apt to be broken.
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  • Tomohiko Tagawa, Yukari Kato, Yoshio Mukai, Shigeo Goto
    1995 Volume 21 Issue 6 Pages 1147-1153
    Published: December 10, 1995
    Released: November 12, 2009
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    Insoluble heteropoly acid catalysts were prepared from H3PW12O40 by partial ion exchange with various alkaline ions. The Friedel-Crafts acylation of toluene with benzoic anhydride in the liquid phase (batch mode, 383K) was carried out in order to apply the strong acidity of these catalysts.
    H0.5Cs2.5PW12O40obtained by partial ion exchange with cesium ion followed by calcination at 573K showed acid strength higher than pKa=-8.2 and exhibited the highest catalytic activity. The reaction was not completed and the final yield of phenyl tolyl ketone (PTK) was about 60% but the activity was comparable to a typical solid super acid catalyst (H2SO4/ZrO2).
    Repeated use of the catalyst showed that incomplete conversion was not caused by irreversible deactivation. Reversible depression of the acylation was explained by; the loss of benzoic anhydride by the reaction of activated benzoic anhydride. with the ketone (PTK) produced, the strong adsorption of the ketone (PTK) produced and of water in the system. The reaction paths were discussed on the basis of the identification of side products. A rate equation was also proposed.
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  • Akira Takano, Tomohiko Tagawa, Shigeo Goto
    1995 Volume 21 Issue 6 Pages 1154-1160
    Published: December 10, 1995
    Released: November 12, 2009
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    Carbon dioxide reforming of methane and carbonaceous deposition were investigated with Al2O3-supported nickel catalysts of different nickel content. Turnover frequency, based on the surface nickel atom, decreased with an increase in the nickel content of the catalyst. The relationship between the turnover frequency and nickel particle size revealed that the reforming reaction mainly took place at the nickel-support boundary. Thermogravimetric analysis was carried out in order to observe carbonaceous deposition which would decrease the catalytic activity. The amount of carbonaceous deposit became smaller in a catalyst of lower nickel content, in other words, a catalyst with smaller nickel particles. This would be due to the suppression of formation of carbon whiskers. The relationship between the catalytic activity and the amount of carbonaceous deposit was discussed. Catalytic activity was not damaged seriously by the carbonaceous deposition which was enough to cover the nickel surface. These results suggested that the reforming reaction and carbonaceous deposition took place at different nickel sites
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  • Yue-Zhou Wei, Kenji Takeshita, Masami Shimizu, Mikio Kumagai, Yoichi T ...
    1995 Volume 21 Issue 6 Pages 1161-1169
    Published: December 10, 1995
    Released: November 12, 2009
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    In order to evaluate the deactivation of a hydrophobic Pt/SDBC catalyst used for a hydrogen isotopic exchange reaction, changes over time in the reaction rate of H2/HDO (v) isotopic exchange over the catalyst induced by the addition of nitric acid, nitrates and nitrogen oxides were studied experimentally. Deactivation was discussed in terms of the balance of the active sites.
    The catalyst was poisoned by HNO3 reversibly and the poisoning was well explained in terms of the competitive adsorption of HNO3 with H2 or HDO onto the catalytic active sites. The poisoning kinetics were explained by the Zeldovich rate equation.
    Neutral nitrates of fission products such as Sr (NO3) 2 showed negligible poisoning effects on the catalyst. ZrO (NO3) 2 showed very similar poisoning behavior with HNO3, and this was considered to result from hydrolysis reactions which produced HNO3.
    No deactivation was observed by the introduction of NO, NO2 or NH3 into the reactor. Instead of poisoning, the reaction rate was accelerated by NO or NO2 and this was considered to be due to local heating of the catalyst surface by exothermic reactions between nitrogen oxides and hydrogen.
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  • Kimihiko Sugiura, Kazutomo Ohtake
    1995 Volume 21 Issue 6 Pages 1170-1178
    Published: December 10, 1995
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    The extent to which a polluted reforming catalyst affects the hydrogen generation in a DIR-MCFC has been experimentally studied. It has been found that the amount of generated hydrogen decreased exponentially with increasing pollution.
    In order to identify the process by which catalyst pollution can induce hydrogen depletion, we adopted the approach of reaction kinetics and carried out a surface analysis of the catalyst, assuming the following three processes may be the answer. (1) transition from reaction-controlled stage to diffusion-controlled stage, (2) decrease in the active surface of the reforming catalyst, and (3) Ni changed compound. The main results are; (1) reaction stage can be reaction-controlled because Effective factor _??_ 1 and drop ratio of partial pressure of CH4 both in the bulk and the catalyst surface is 23%, (2) from EPMA and XRD, it was found that the Ni in the catalyst was not a compound but pure, and that the Ni concentration on the catalyst's surface decreased with increasing pollution.
    Therefore, it can be concluded that the pollution of the catalyst is caused mainly by the decrease of its active surface, due to the physical absorption of molten carbonate by the Ni included in the catalyst.
    In addition, we have also studied the upper limit of the pollution in operating a DIR-MCFC and found that a DIR-MCFC cannot be normally operated when the pollution exceeds about 2 cut.
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