佐藤 智司

Production method of spherical silica beads with macropores was investigated from water glass. Spherical beads with continuous macropores were obtained by inducing phase separation in sol droplets in an organic solvent, and the diameter of beads was controlled between 0.7 and 2.8 mm by changing volume of droplets. The macroporous silica beads have dense external surface layer with thickness of ca. 2μm. The surface layer was removed by soaking the wet gel in 1 mol dm-3 HF solution for 10s before drying.

A catalytic reactor using a capillary column with Cu/SiO₂ layer on its inner surface was prepared by injecting a silica sol containing Cu ions in a fused silica capillary and by subsequent gelation under the conditions controlled in order to deposit silica gel uniformly on the inner wall of the capillary. Its catalytic activity was demonstrated in the hydrogenation of propene by constructing a pulse reactor using the catalyst capillary and a separation capillary with pure silica gel layer.

Monolithic polycrystalline zeolites with through-macropores were prepared by steam treatment of bimodal porous silica gel monolith in the presence of tetrapropylammonium hydroxide, where the bimodal porous silica gel was prepared by inducing phase separation during sol-gel process. The silica skeleton with mesopores was transformed into polycrystalline zeolites maintaining continuous macropore morphology and monolithic shape. In the zeolites, there are three different pores arranged hierarchically: through-macropores originally existed in the precursor silica gel, small macropores at interstitial of zeolite crystallites, and micropores in zeolite framework.

Glass capillaries with silica gel layer on the inner surface were prepared by applying phase separation during sol-gel reaction of tetraethyl orthosilicate in the presence of poly (ethylene glycol) with number-average molecular weight of 20000. According to this technique, we can coat the internal surface with uniform silica gel layer for silica capillary with diameter up to 0.1 mm. In the gas chromatographic analysis of hydrocarbons using the capillary column with silica gel layer, light hydrocarbons up to C4 can be analyzed with high resolution and within short experimental time at ambient temperature.

Thermal properties of bimodal porous silica and silica-zirconia with humidity control ability are investigated in order to clarify their potential as a multi-functional building material. Thermal conductivity of the silica decreases with increasing the porosity of the silica, and 0.06 W m(-1)K(-1) is achieved when the porosity exceeds 90%. The silica shows thermal resistance of ca. 800degreesC, which is much higher than conventional thermal insulators. The thermal resistance can be improved by the addition of zirconia: a silica-zirconia sample maintains its high porosity up to 1050degreesC. Thus, the bimodal porous silica and silica-zirconia are expected to be a thermal insulator with humidity control and thermal resistance abilities.

Glass capillaries with silica gel layer on the inner surface were prepared by applying phase separation during sol-gel reaction of tetraethyl orthosilicate in the presence of poly (ethylene glycol) with number-average molecular weight of 20000. According to this technique, we can coat the internal surface with uniform silica gel layer for silica capillary with diameter up to 0.1 mm. In the gas chromatographic analysis of hydrocarbons using the capillary column with silica gel layer, light hydrocarbons up to C4 can be analyzed with high resolution and within short experimental time at ambient temperature.

Thermal properties of bimodal porous silica and silica-zirconia with humidity control ability are investigated in order to clarify their potential as a multi-functional building material. Thermal conductivity of the silica decreases with increasing the porosity of the silica, and 0.06 W m<-1>K^<-1> is achieved when the porosity exceeds 90%. The silica shows thermal resistance of ca. 800℃, which is much higher than conventional thermal insulators. The thermal resistance can be improved by the addition of zirconia: a silica-zirconia sample maintains its high porosity up to 1050℃. Thus, the bimodal porous silica and silica-zirconia are expected to be a thermal insulator with humidity control and thermal resistance abilities.

Humidity control ability of monolithic bimodal porous silica gel prepared from water glass in the presence of poly (acrylic acid) was investigated from the viewpoints of both equilibrium and kinetic aspects. The humidity, at which adsorption-release of water vapor occurred reversibly, was systematically controlled by changing the mesopore size. The equilibrium adsorption amount of water was as high as 0.7 g per gram of silica. In addition, the presence of macropores made it possible to quickly response for humidity change by the adsorption-release cycle because of rapid gas diffusion in monolithic gel body. These features are quite attractive as a material for humidity control in the airtight buildings.

Catalytic dehydration of 1,4-butanediol was investigated at temperatures of 200-450 degreesC. In the dehydration of 1,4-butanediol, homoallyl alcohol such as 3-buten-1-ol is produced over pure CeO2. The formation of 3-buten-1-ol is followed by the stepwise dehydration to 1,3-butadiene. CeO2 can produce 3-buten-1-ol without catalyzing the further dehydration: the maximum selectivity of 68.1 mol% and the yield of 59.7% are attained at 400 degreesC. (C) 2004 Elsevier B.V. All rights reserved.

Post-treatment of reduced copper catalyst, which contains Zn, Zr, and Al, with alkaline solution is effective in improving the selectivity to ethyl acetate in the dehydrogenative dimerization of ethanol. The treatment with Na2CO3 and K2CO3 greatly suppressed the formation of by-products such as butanone and 2-butanol, and resulted in the improvement of the selectivity to ethyl acetate. The suppression of butanone and 2-butanol is caused by the neutralization of surface acid sites that are active for the dehydration from 1,3-butanediol, into which acetaldol is hydrogenated. These acid-sites are formed after reduction of the Cu-Zn-Zr-Al-O mixed oxide precursor, and thus the post-treatment is effective. We also discuss the reaction routes in the side reactions. (C) 2004 Elsevier B.V All rights reserved.

Synthesis of gamma-butyrolactone (GBL) from 1,4-butanediol (BDO) over copper-based catalysts with ZnO, Al2O3 and ZrO2 was investigated. Catalytic activity of copper was greatly affected by the additive oxides. The highest activity was obtained at a catalyst molar ratio of CuO:ZnO:ZrO2:Al2O3 = 6:1:2:2. ZrO2 showed the highest additive effect for the GBL synthesis with enhancing dehydrogenation ability of metallic Cu and enlarging Cu surface area. Al2O3 enlarged Cu surface area, whereas a large amount of tetrahydrofuran (THF) was formed over the acid sites of Al2O3 surface, and ZnO reduced the THF yield. The reaction pathway from BDO to GBL was also clarified: BDO was initially dehydrogenated to 4-hydroxybutanal, which was immediately hemiacetalized to 2-hydroxytetrahydrofuran, followed by the dehydrogenation to GBL over metallic Cu. (C) 2003 Elsevier B.V. All rights reserved.

Pressure loss in gas flow in three-dimensionally interconnected macropores in silica gel rods was investigated. In the preparation of the silica gel, the continuous macropores are formed by inducing phase separation in a solution containing tetraethoxysilane (TEOS) and poly (ethylene oxide) (PEO), and subsequent freezing of its transitional structures by gelation. Average macropore size of the silica gels was systematically controlled from 25 to 0.6 mum by changing PEO content in the solution without affecting porous morphology. The pressure loss in gas flow in the continuous macropores can be approximated with a simple straight channels model, and well reproduced with the Hargen-Poiseuille's equation without any correction, in contrast to that in columns packed with micrometer-size particles, which show substantial higher pressure loss than the continuous macropores. The low flow resistance in the macroporous silica rods would be attributed to the absence of necks in flow pathways.

Humidity control ability of monolithic bimodal porous silica gel prepared from water glass in the presence of poly (acrylic acid) was investigated from the viewpoints of both equilibrium and kinetic aspects. The humidity, at which adsorption-release of water vapor occurred reversibly, was systematically controlled by changing the mesopore size. The equilibrium adsorption amount of water was as high as 0.7 g per gram of silica. In addition, the presence of macropores made it possible to quickly response for humidity change by the adsorption-release cycle because of rapid gas diffusion in monolithic gel body. These features are quite attractive as a material for humidity control in the airtight buildings.

Pressure loss in gas flow in three-dimensionally interconnected macropores in silica gel rods was investigated. In the preparation of the silica gel, the continuous macropores are formed by inducing phase separation in a solution containing tetraethoxysilane (TEOS) and poly (ethylene oxide) (PEO), and subsequent freezing of its transitional structures by gelation. Average macropore size of the silica gels was systematically controlled from 25 to 0.6μn by changing PEO content in the solution without affecting porous morphology. The pressure loss in gas now in the continuous macropores can be approximated with a simple straight channels model, and well reproduced with the Hargen-Poiseuille's equation without any correction, in contrast to that in columns packed with micrometer-size particles, which show substantial higher pressure loss than the continuous macropores. The low flow resistance in the macroporous silica rods would be attributed to the absence of necks in flow pathways.

CeO2 catalyzed the selective dehydration of 1,3-diols into allylic alcohols at temperatures 300-375degreesC. In the dehydration of 1,3-propanediol over pure CeO2, 2-propen-1-ol is produced with the maximum selectivity of 98.9 mol% at 325degreesC. In the dehydration of 1,3-butanediol, 2-buten-1-ol and 3-buten-2-ol were produced with the sum of the selectivity &gt; 99 mol% over CeO2, which showed attractive catalytic performance without decay at temperatures &lt;375degreesC. In the reactions of 2-buten-1-ol, 1,2- and 1,4-butanediol, little dehydrated products were detected over the CeO2. (C) 2002 Elsevier Science B.V. All rights reserved.

Fine particles of SiO2-coated Fe2O3 were prepared by depositing silica on an iron(III) hydroxide precipitate using tetraethoxysilane (TEOS). The silica deposition proceeded under mild conditions at 20 degreesC; crystallization hardly occurred and silica loading was controlled by the amount of TEOS charged, whereas the precipitate crystallized to a mixture of FeO(OH) and alpha-Fe2O3 under hydrothermal conditions. The specific surface area of the SiO2-coated Fe2O3 increased with silica loading, and exceeded 280 m(2) g(-1) even after calcination at 500 degreesC. The silicate species deposited on the precipitate of iron(III) hydroxide prevented the primary particles from agglomerating during calcination, resulting in the high surface area and hard reducibility of the SiO2-Fe2O3.

Mesoporous zirconia was prepared by the hydrolysis of zirconium tetrapropoxide (ZTP). Crystal structure of zirconia was controlled by using different hydrolysis procedures. A large amount of water and subsequent calcination led to the formation of mesoporous monoclinic zirconia with the pore size of 20 nm, while nonporous tetragonal zirconia was prepared with a small amount of water. Mesoporous tetragonal zirconia with controlled pore size was prepared from ZTP and carboxylic acids with different alkyl-chain length. The average pore size of the tetragonal zirconia increased from 4.8 to 7.5 nm with increasing alkyl-chain length of carboxylic acids. A complex of ZTP and carboxylic acid formed a hexagonal mesophase at the molar ratio of carboxylic acid to ZTP greater than or equal to 1.5. The lattice parameter of the hexagonal mesophase increased with increasing alkyl-chain length of carboxylic acid. The hexagonal mesophase, however, disappeared when the precursor melted over 58degreesC. The calcined zirconia consisted of the aggregates of crystallites, and the mesopores were located at interparticles. The appropriate coordination state and alkyl-chain length of carboxylic acid are probably effective in preparing mesoporous tetragonal zirconia and controlling the mesopores.

Mesoporous zirconia was prepared by the hydrolysis of zirconium tetrapropoxide (ZTP). Crystal structure of zirconia was controlled by using different hydrolysis procedures. A large amount of water and subsequent calcination led to the formation of mesoporous monoclinic zirconia with the pore size of 20 nm, while nonporous tetragonal zirconia was prepared with a small amount of water. Mesoporous tetragonal zirconia with controlled pore size was prepared from ZTP and carboxylic acids with different alkyl-chain length. The average pore size of the tetragonal zirconia increased from 4.8 to 7.5 nm with increasing alkyl-chain length of carboxylic acids. A complex of ZTP and carboxylic acid formed a hexagonal mesophase at the molar ratio of carboxylic acid to ZTP &ge; 1.5. The lattice parameter of the hexagonal mesophase increased with increasing alkyl-chain length of carboxylic acid. The hexagonal mesophase, however, disappeared when the precursor melted over 58℃. The calcined zirconia consisted of the aggregates of crystallites, and the mesopores were located at interparticles. The appropriate coordination state and alkyl-chain length of carboxylic acid are probably effective in preparing mesoporous tetragonal zirconia and controlling the mesopores.

Direct synthesis of ethyl acetate from ethanol over a Cu-Zn-Zr-Al-O catalyst was investigated under pressured conditions between 473 and 533 K. Both the selectivity to ethyl acetate and the space-time yield of ethyl acetate increase with increasing reaction pressure, whereas ethanol conversion decreases. The highest space-time yield of ethyl acetate is attained at a reaction pressure of about 0.8 MPa with maximum selectivity of 93 wt%. During the process, ethanol is first dehydrogenated to acetaldehyde and is then coupled with another ethanol molecule to form hemiacetal, which is further dehydrogenated to ethyl acetate. The concentration of by-products such as 1-butanol and butanone, which form after the aldol addition of acetaldehyde, decreases with increasing reaction pressure. Since the equilibrium of the dehydrogenation of ethanol to acetaldehyde shifts to an ethanol-rich composition at high pressure, the decrease in the partial pressure of acetaldehyde explains the suppression of the by-products formed through acetaldol. (C) 2002 Elsevier Science (USA).

Various metal oxides coated with a thin silica layer were prepared by two different liquid-phase deposition methods; one is the deposition of silica on the corresponding metal hydroxides using tetraethyl orthosilicate (TEOS), and the other is the hydrothermal treatment of the metal hydroxides with silica glass in basic solution. The TEOS treatment is more effective for depositing silica on the precursor hydroxides than the hydrothermal treatment employing the process of dissolution-deposition of silica. The. silica-coated metal oxides of MgO, Fe2O3, NiO, Y2O3, ZrO2, SnO2, and Dy2O3 have high specific surface areas &gt; 200 m(2)g(-1) after heating at 773 K.

Direct synthesis of ethyl acetate from ethanol is investigated over several copper catalysts. We clarified the role of additive metal oxides such as ZrO2, ZnO and Al2O3. An additive ZrO2 gives ester-formation activity to the pure copper catalyst. ZnO suppresses the formation of undesirable products such as methyl ethyl ketone (MEK) under the co-existence of ZrO2. Al2O3 enhances not only the conversion of ethanol but also the catalytic activity for the side reaction of aldol addition of acetaldehyde. Ethanol is converted into ethyl acetate with high selectivity over Cu-ZnO-ZrO2-Al2O3 catalyst, together with low selectivity to methyl ethyl ketone. Then we investigated the influence of copper content in the quaternary copper catalysts containing ZrO2, ZnO and Al2O3 on the catalytic performance. The ethyl acetate production ability of catalyst is roughly proportional to the Cu surface area of the Cu-ZnO-ZrO2-Al2O3 catalyst. The highest ethanol conversion, the highest ethyl acetate selectivity, and the highest space-time yield of ethyl acetate were achieved at Cu content of 70 mol%. (C) 2002 Elsevier Science B.V. All rights reserved.

Fine particles Of SiO2-coated Ni metal were prepared by depositing silica on a Ni(OH)(2) precipitate in a dissolution-deposition process of silica glass under hydrothermal conditions, followed by calcination and reduction. A fresh precipitate of Ni(OH)(2) was heated with a NaOH solution containing several pieces of silica glass chips in a pressure vessel at 100 degreesC. Silica components dissolved from the glass chips were deposited on the Ni(OH)(2) precipitate, and the silica loading increased with increasing the hydrothermal period. Even after calcination at 500 degreesC, a specific surface area of the resulting SiO2-NiO increased with silica loading, and exceeded 200 m(2) g(-1). SiO2-NiO, reduced at 500 degreesC, had a metal surface area as high as 22 m(2) g(-1). In contrast to the fact that pure Ni(OH)(2) readily aggregates during heating, the SiO2-coated Ni(OH)(2) particles are protected from agglomerating during the hydrothermal process, calcination, and reduction.

The liquid-phase hydrogenation of ketones was investigated over Raney nickel and Ni-MgO catalysts with known pore structures: the effects of the sizes of the reactant and solvent on the catalytic activity were examined at 0degreesC at a hydrogen pressure of 1.1 MPa to discuss the mass transfer of reactants/products and solvents within the mesopores. The catalytic activity decreases linearly with increasing reactant molecular size in the hydrogenation of both aliphatic and aromatic ketones with an acetyl group, such as acetone, butan-2-one, heptan-2-one, nonan-2-one, undecan-2-one, acetophenone, 4'-methylacetophenone, 4'-ethylacetophenone, and 4'-n-propylacetophenone. In the hydrogenation of ketones such as acetone, cyclohexanone, and heptan-4-one in linear alkane solvents, the catalytic activity decreases with the increasing length of the carbon chain of the solvent, and a zigzag phenomenon, i.e. the catalytic activity in alkane solvents with an odd number of carbons in the chain is higher than in those with an even number of carbons, is observed for larger reactants in smaller pores. Neither the activity drop nor the zigzag tendency appears for smaller reactants reacted in sufficiently large mesopores. It can be concluded that strong resistance for the mass transfer of larger reactants in smaller mesopores explains the difference in the catalytic hydrogenation reactivity of reactant diffusing through solvent in a mesoporous catalyst.