里川 重夫

The adsorption of arsenic from aqueous solution on synthetic zeolites H-MFI-24(H24) and H-MFI-90(H90) with MFI topology has been investigated at room temperature (r.t) applying batch equilibrium techniques. The influences of different sorption parameters such as contact time. solution pH, initial arsenic concentration and temperature were also studied thoroughly in order to optimize the reaction conditions. The adsorption of arsenic on to H24 and H90 follows the first-order kinetics and equilibrium time was about 100 min for both the adsorbents. The first-order rate constant (k), 4.7 x 10(-3) min(-1) for H90 is more than two times higher in magnitude compared to 2.1 x 10(-3) min(-1) for H24. Adsorption performance of H90 is higher compared to H24 due to it's highly mesoporous nature which in turn accelerates the diffusion process during adsorption. As(V) sorption capacity derived from Langmuir isotherm for H24 and H90 are 0.0358 and 0.0348 g g(-1), respectively. Arsenic uptake was also quantitatively evaluated using the Freundlich and Dubinin-Kaganer-Raclushkevich (DKR) isotherm models. Ion exchange between adsorbent's terminal aluminol groups with different predominant forms of arsenate in solution is one of the various important reactions occurred during adsorption process. (c) 2008 Elsevier B.V. All rights reserved.

The complexes [Co(N<boolean AND>O)(2)] (1) and [Cu(N<boolean AND>O)(2)] (2) (N<boolean AND>O = eta(2)-(N,O) coordinated 2-pyrazinecarboxylic acid) have been synthesized and characterized by elemental (including metal) analyses, FT-IR spectroscopy and powder X-ray diffraction. The molecular structure of complex 2 was determined by single X-ray crystallography. In the molecule, the Cu atom occupies the center of a square planar geometry, which consists of two trans-O atoms and two trans-N atoms of two 2-pyrazinecarboxylic acid ligands. The complexes 1 and 2 were well encapsulated into zeolite-Y super-cage to yield the corresponding zeolite-Y encapsulated metal complexes, abbreviated herein as [Co(N<boolean AND>O)(2)]-Y (3) and [Cu(N<boolean AND>O)(2)]-Y (4). Similarly, the metal complexes 1 and 2 were immobilized on alumina and organically modified silica surfaces to lead to the formation of immobilized metal complexes [Co(N<boolean AND>O)(2)]-Al(2)O(3) (5); [Cu(N<boolean AND>O)(2)]-Al(2)O(3) (6); [Co(N<boolean AND>O)(2)]-AMPS (7) and [Cu(N<boolean AND>O)(2)]-AMPS (8) (AMPS= aminopropyl silica). Elemental (including metal) analyses, FT-IR spectroscopy, powder X-ray diffraction and thermal analysis have been used to characterize these materials. The catalytic activity of all the catalysts 1-8 towards the oxidation of cyclohexene into different chemically and pharmaceutically important products were evaluated under homogeneous and heterogeneous conditions. In order to obtain a maximum conversion of cyclohexene, the reaction parameters, like reaction temperature and time, were optimized. Under the optimized conditions, a maximum of 90.47% cyclohexene conversion was achieved with [Cu(N<boolean AND>O)(2)]-Y (4) with a 1:2 molar ratio reaction of cyclohexene and H(2)O(2). (c) 2008 Elsevier Ltd. All rights reserved.

PEFC用の水素製造プロセスにおける微量のCO除去方法として、新たにCOメタン化反応が注目を集めている。COメタン化反応は装置の制御が簡便化できるという利点を有するが、改質ガス中に含まれるCO₂のメタン化が同時に進行すると熱暴走する危険性がある。本研究ではCOメタン化反応の選択性の向上を目的とし、担持Ru触媒を用いて、Ru粒子径や担体のCOメタン化反応選択性への影響について検討した。

改質ガス中の微量CO除去を目的とし、CO選択メタン化反応用Ru触媒について検討を行った。種々の金属酸化物を担体としたRu触媒について検討したところ、活性および選択性は担体によって大きく異なり、アルミナやチタニア、Y型およびベータ型ゼオライトを用いることで、従来の商業触媒以上に使用可能な温度域が広がった。特に低温活性の高かったRu/TiO2触媒について、チタニアの調製条件やRuの担持条件などの触媒調製条件がRu/TiO2触媒の活性選択性に与える影響について検討した。

For this study, we established and evaluated two usage scenarios of ethanol (EtOH) from biomass for transportation: direct use of ethanol and use of hydrogen produced from EtOH. As a result, we examined the effectiveness of fuel cell vehicles of the latter case. In the EtOH direct-use scenario, the EtOH-to-Tank efficiency was 63.6-81.0% (energy loss: 706-289 kJ/mol) with 30% Tank-to-Wheel efficiency of EtOH hybrid cars. In other words, in the scenario of fuel cell vehicles with 60% Tank-to-Wheel efficiency, the efficiency of EtOH-to-Tank should be more than 31.8-40.5%. From the results of the present study, it can be concluded that the two evaluated scenarios have comparative efficiencies, considering the currently published EtOH-to-Tank efficiency using steam reforming of 34.0-43.0%. For the realization of bioEtOH-oriented fuel cell vehicles, the development of higher hydrogen production efficiency is required.

TiO2/SiO2/Fe3O4 composite was synthesized by sol-gel technique for silica and titania coatings on magnetite core to enable recovery after photocatalytic degradation. Carbon coating was also carried out by calcination of TiO2/SiO2/Fe3O4 under nitrogen atmosphere in presence of PVA as a source of carbon to enhance the adsorption of organic compounds on catalyst surface and to get better activity. All prepared samples were characterized using EDX, CN analyzer, XRD, BET and SEM. Degradation of methyl orange dye was used to assess the photocatalytic performance of the prepared samples. Calcination temperature was found to affect rate of reaction because of the formation of rutile phase at high calcination temperature. Carbon coated samples unexpectedly exhibited lower rate of reaction at almost all calcination temperatures. (c) 2007 Elsevier B.V. All rights reserved.

The acrylic monomer, 4-cyanophenyl acrylate (CPA), was synthesized by reacting 4-cyanophenol dissolved in methyl ethyl ketone (MEK) with acryloyl chloride in the presence of triethylamine as a catalyst. The homopolymer and copolymers were synthesized by using free-radical techniques. Characterization by FTIR, H NMR, and C-13 NMR spectroscopic analysis confirms the chemical structure. The solubility of the polymers was tested in various polar and nonpolar solvents. The polydispersity index values of polymers suggest a strong tendency for chain termination by disproportionation in all cases, and the tendency increases with the increasing GMA content in the feed. The initial decomposition temperatures for poly(GMA) (188 degrees C), poly(CPA-co-GMA) (280 degrees C), and poly(CPA) (290 degrees C) reveal that the thermal stability of the copolymer increases with an increase in CPA content. DSC analysis showed T. for poly(CPA) (25 degrees C), poly(GMA) (74 degrees C), and copolymer (0.4007 : 0.5993) (39 degrees C) indicates that T-g of the copolymers decreases with the increase in CPA content. The copolymer composition was determined using H-1 NMR spectra. The monomer reactivity ratios were determined by the application of linearization methods such as Fineman-Ross (r(1) = 0.5806, r(2) = 0.6651), Kelen-Tudos (r(1) = 0.5442, r(2) = 0.6472), and extended Kelen-Tudos methods (r(1) = 0.5372, r(2) = 0.6352). The reactivity ratio values indicate that the copolymerization has a tendency to alternation. (c) 2008 Wiley Periodicals, Inc.

Ozonolysis of triacylglycerol was carried out over heterogeneous catalysts. The triacylglycerol was decomposed to some compounds with low boiling points containing hydrocarbons, aldehydes, ketones, fatty acids and lactones over H-Y zeolite catalyst at 353-423 K. The amounts of products were strongly dependent on the properties of catalysts and reaction conditions.

This paper describes the preparation of several new transparent and very fine crystal glass-ceramics from the BaO-B2O3 system utilizing an appropriate additive of fluorides, partial replacement of B2O3 by SiO2, and introducing nucleating agents, such as TiO2. The physical properties of the prepared materials and the changes with varying base glass compositions and heat treatment programs were investigated. The thermal behavior and microstructure of the developed phases were characterized using DTA, XRD, and SEM. Glass-ceramics with marked transparency were prepared. These transparent derivatives owe their transparency to the distinctive properties of the nano-crystalline samples. The dielectric constant of transparent glass-ceramics samples at 100 kHz were between 14-20, which is very suitable for a wide range of applications, such as the highspeed switching of large-scale integrators. It was found that the addition of F- and SiO2 greatly influenced the transparency of the produced glass-ceramics. Also, the addition of TiO2 greatly enhanced transparency, in spite of increasing cutoff in the UV region to a higher wavelength. (C) 2008 The Ceramic Society of Japan. All rights reserved.

The pure and fine silica particles are widely used in the semiconductor industries. In our previous paper, the authors have demonstrated that production of title silica powder is possible by gas phase hydrolysis of tetramethoxysilane (TEMS). In this paper, we report the effect of the shape of reactor and operational condition, such as mixing condition and temperature on conversion of the reaction and properties especially particle diameter of produced silica fine particles. The different shapes of reactors named as Type 1, Type 2, and Type 3, were tested. In Type 1, H2O and TEMS were introduced cocurrently and heated in the reactor. On the other hand, in Types 2 and 3, TEMS introduced from the top was vigorously mixed, at relatively upper and rather vicinity of the center parts respectively, with heated H2O introduced from the bottom through the center part of the reactor. Thus TEMS is mixed with more heated water in case of Types 2 and 3 than Type 1. Type 3 has a shorter water introduction pipe and TEMS and H2O are mixed at higher temperature than Type 2. The average diameters were decreased as the order of Type 1, Type 2 and Type 3. It was demonstrated that smaller fine particles were produced by rapid heating of TEMS under coexistence of water vapor. Under the condition, only nucleation reaction is expected to be accelerated, by Suppressing particle growth through heterogeneous reaction. The mixture condition of the gas leading to the heating condition of TEMS with water vapor Could be changed by changing the shape of reactor, which resulted in the change in averaged diameter of the produced silica particles.

In this study, we used iron powder and hydrogen peroxide, and investigated the kinetics of decomposition of TCE by the Fenton's reaction. As a result, the decomposition of TCE with iron powder was found to occur after some introduction period, which is not observed for that with ferrous iron. Excepting the period, the decomposition rate was found to be analyzes as the first order reaction. The obtained first reaction constants are found to be proportional to the iron powder concentration, but the reaction order to hydrogen peroxide changed with the range of its concentration. At its relatively high concentration of hydrogen peroxide, the reaction order for the concentration of hydrogen peroxide became negative.

A commercial grade carbon black was chemically modified using mineral acids (either with HNO3 or H2SO4 or mixture) and the sorption performance of the virgin and modified forms were investigated. Chemical modification resulted in the creation of surface acidic functional groups (-COOH, -SO2OH) and was verified by FTIR spectra. This was further verified by TGA analysis revealing higher weight loss characteristics of the modified carbons in comparison to virgin carbon black. Morphological changes were observed from BET surface area measurements and SEM analysis. XRD study revealed the change of graphitic crystallite size as a result of modification. The suspension pH of the materials in deionized water and the point of zero charge (pH(pzc)) in inert electrolyte were determined. The measured values of suspension pH and pHpzc for all the carbons were found to be acidic with more acidic character in the modified carbons. These materials were used as sorbents for the removal of arsenic from aqueous medium and showed excellent adsorption performance. (C) 2007 Elsevier B.V. All rights reserved.

A novel methacrylic monomer, 4-cyanophenyl methacrylate (CPM) was synthesized by reacting 4-cyanophenol dissolved in methyl ethyl ketone (MEK) with methacryloyl chloride in the presence of triethylamine as a catalyst. Copolymers of CPM with methyl methacrylate(MMA) at different composition was prepared by free radical solution polymerization at 70 +/- 1 degrees C using benzoyl peroxide as initiator. The copolymers were characterized by FT-IR, H-1-NMR and C-13-NMR spectroscopic techniques. The solubility of the polymers was tested in various polar and non polar solvents. The molecular weight and polydispersity indices of the copolymers were determined using gel permeation chromatography. The glass transition temperature of the copolymers increases with increase in mole fraction of MMA content. The thermal stability of the copolymer increases with increases in mole fraction of CPM content in the copolymer. The copolymer composition was determined by using H-1-NMR spectroscopy. The monomer reactivity ratios estimated by the application of linearization methods such as Fineman-Ross (r(1)=2.524 +/- 0.038, r(2)=0.502 +/- 0.015), Kelen-Tudos (r(1)=2.562 +/- 0.173, r(2)=0.487 +/- 0.005) and extended Kelen-Tudos methods (r(1)=2.735 +/- 0.128, r(2)=0.4915 +/- 0.007).

Addition of H-2 in the lean exhausts significantly improves the NOx reduction activities at low temperatures by hydrocarbons over Ag/Al2O3 catalyst. This discovery "hydrogen effect" provides a novel approach to the design of SCR systems. We concluded that the catalytic activity is promoted by the reductive activation of O-2 with H-2 and the production of moderately agglomerated Ag-n(delta+) clusters on the catalyst surface. However, the other research groups concluded that the formation of Ag-n(delta+) cluster is not essential for the enhancement of the SCR activity and it is proposed that hydrogen itself participates directly in the reaction mechanism. Although the mechanism of the "hydrogen effect" is under debate, the oxidative activation of hydrocarbons is the key step to obtain high SCR activity at lower temperatures. (c) 2007 Elsevier Ltd. All rights reserved.

Magnetically separable TiO2/SiO2/Fe3O4 Composites of different core (Fe3O4) diameters and silica contents have been prepared by sol-gel technique for both silica and titania coatings. Energy dispersive X-ray fluorescence (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area analysis and scanning electron microscope (SEM) have been used for characterization of prepared samples. Photocatalytic activity of the prepared samples has been investigated by photodegradation of methyl orange. Obtained results have shown that 25-45 mu m core diameter exhibits the maximum activity since it possesses a convenient surface area and light transmittance. Silica content has a significant effect on the activity of composite. Silica content of more than 10 wt% has reduced the catalyst activity because of the increase in particle diameter and reduction of surface area. (C) 2007 Elsevier Masson SAS. All rights reserved.

A new methacrylic monomer, 4-nitro-3-methylphenyl methacrylate (NMPM) was prepared by reacting 4-nitro-3-methyl phenol dissolved in methyl ethyl ketone (MEK) in the presence of triethylamine as a catalyst. Copolymerization of NMPM with methyl methacrylate (MMA) has been carried out in methyl ethyl ketone (MEK) by free radical solution polymerization at 70 +/-+ VC utilizing benzoyl peroxide (BPO) as initiator. Poly (NMPM-co-MMA) copolymers were characterized by FT-IR, H-1-NMR and C-13-NMR spectroscopy. The molecular weights (M-w and M-n) and polydispersity indices (M-w/M-n) of the polymers were determined using a get permeation chromatograph. The glass transition temperatures (T,) of the copolymers were determined by a differential scanning calorimeter, showing that T-g increases with MMA content in the copolymer. Thermogravimetric analysis of the polymers, performed under nitrogen, shows that the stability of the copolymer increases with an increase in NMPM content. The solubility of the polymers was tested in various polar and non-polar solvents. Copolymer compositions were deter-mined by H-1-NMR spectroscopy by comparing the integral peak heights of well separated aromatic and aliphatic proton peaks. The monomer reactivity ratios were determined by the Fineman-Ross (r(1) = 7.090:r(2) = 0.854), Kelen-Tudos (r(1) = 7.693: r(2) = 0.852) and extended Kelen-Tudos methods (r(1) = 7.550: r(2)= 0.856).

Improvement of mechanical properties of cordierite glass-ceramics using modified Egyptian basalt rocks by addition of different amounts of zirconia (ZrO2) was investigated. Crystallization behavior of modified basalt glass was studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). The Vickers hardness of glass-ceramics containing different amounts of ZrO2 and formed at 1050 degrees C for various heat-treatment time was compared. Toughness of the glass-ceramics increased with increasing the amount of transformable ZrO2, which process is probably caused by crack deflection due to the high stress field around transformed ZrO2.

The methacrylic monomer, 4-biphenylmethacrylate (BPM) was synthesized by reacting 4-biphenyl phenol dissolved in ethyl methyl ketone (EMK) with methacryloyl chloride in presence of triethylamine as a catalyst. The copolymers of BPM with glycidyl methacrylate (GMA) were synthesized by free radical polymerization in EMK solution at 70 +/- 1 degrees C using benzoyl peroxide as a free radical initiator. The copolymerization behaviour was studied in a wide composition interval with the mole fractions of BPM ranging from 0.15 to 0.9 in the feed. The copolymers were characterized by FT-IR, H-1-NMR and C-13-NMR spectroscopic techniques. The solubility was tested in various polar and non polar solvents. The molecular weight and polydispersity indices of the polymers were determined using gel permeation chromatography. The glass transition temperature of the copolymers increases with increase in BPM content. The thermogravimetric analysis of the polymers showed that the thermal stability of the copolymer increases with BPM content. The copolymer composition was determined using H-1-NMR spectra. The monomer reactivity ratios were determined by the application of conventional linearization methods such as Fineman-Ross (r(1)=0.392 +/- 0.006, r(2) = 0.358 +/- 0.007, Kelen-Tudos (r(1)= 0.398 +/- 0.004, r(2)= 0.365 +/- 0.013) and extended Kelen-Tudos methods (r(1)= 0.394 +/- 0.004, r(2)= 0.352 +/- 0.006).

The novel methacrylic monomer, 4-nitro-3-methylphenyl methacrylate (NMPM) was synthesized by reacting 4-nitro-3methylphenol dissolved in ethyl methyl ketone (EMK) with methacryloyl chloride in the presence of triethylamine as a catalyst. The homopolymer and copolymers of NMPM with glycidyl methacrylate having different compositions were synthesized by free radical polymerization in EMK solution at 70 +/- 1 degrees C using benzoyl peroxide as free radical initiator. The homopolymer and the copolymers were characterized by FT-IR, H-1 NMR and C-13 NMR spectroscopic techniques. The solubility tests were tested in various polar and non-polar solvents. The molecular weight and polydispersity indices of the copolymers were determined using gel permeation chromatography. The glass transition temperature of the copolymers increases with increase in NMPM content. The thermogravimetric analysis of the polymers performed in air showed that the thermal stability of the copolymer increases with NMPM content. The copolymer composition was determined using H-1 NMR spectra. The monomer reactivity ratios were determined by the application of conventional linearization methods such Fineman-Ross (r(1) = 1.862, r(2) = 0.88 1), Kelen-Tudos (r(1) = 1.712, r(2) = 0.893) and extended Kelen-Tudos methods (r(1) = 1.889, r2 = 0.884). (C) 2007 Elsevier Ltd. All rights reserved.

Vapor-phase adsorptive removal of tert-butanethiol (TBT) over silver nitrate supported on silica (AgSi) and silica-alumina (AgSiAl) is tested under ambient conditions. Saturation uptakes on AgSi and AgSiAl are close to that on Ag-exchanged Y zeolite, which was shown to have high sulfur capacity in the literature. The structural analyses by XRD, TEM, Ag K-edge XANES/EXAFS, and in situ UV-vis show that the reaction of Ag species on these samples with TBT yields AgSH species, Ag2S monomer, Ag4S2 cluster, and Ag2S particles. Dynamic changes in adsorbed intermediates and the silver sulfides were followed by in situ FTIR and in situ UV-vis, and the following reaction mechanism is presented: (1) reaction of Ag+ with TBT to produce butenes and AgSH species; (2) reaction of the two AgSH to produce Ag2S monomer and H2S; (3) aggregation of Ag2S monomer to (Ag2S), clusters and Ag2S particle.

Improvement of mechanical properties of cordierite glass-ceramics using modified Egyptian basalt rocks by addition of different amounts of zirconia (ZrO2) was investigated. Crystallization behavior of modified basalt glass was studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). The Vickers hardness of glass-ceramics containing different amounts of ZrO2 and formed at 1050°C for various heat-treatment time was compared. Toughness of the glass-ceramics increased with increasing the amount of transformable ZrO2, which process is probably caused by crack deflection due to the high stress field around transformed ZrO2.

Co-polymerization of BPM with methyl methacrylate (MMA) has been carried out in methyl ethyl ketone (MEK) by free radical solution polymerization at 70 +/- 1 degrees C utilizing benzoyl peroxide (BPO) as initiator. Poly(BPM-co-MMA) co-polymers were characterized by FT-IR, H-1-NMR and C-13-NMR spectroscopy. The molecular weights (M-w and M-n) and polydispersity indices (M-w/M-n) of the polymers were determined using gel permeation chromatograph. The glass transistion temperatures (T-g) of the co-polymer increases with MMA content. Thermogravimetric analysis of the polymers performed in nitrogen shows that the stability of the co-polymer increases with an increase in BPM content. The solubility of the polymers was tested in various polar and nonpolar solvents. Co-polymer compositions were determined by H-1-NMR spectroscopy by comparing the integral peak heights of well separated aromatic and aliphatic protons peaks. The monorner reactivity ratios were determined using Fineman-Ross (r(1) = 1.70 +/- 0.054, r(2) = 0.065 +/- 0.004), Kelen-Tudos (r(1) = 1.73 0.035, r(2) = 0.077 +/- 0.008) and extended Kelen-Tudos methods (r(1) = 1.866 +/- 0.100, r(2) = 0.069 +/- 0.008).

Through the examination of stability of exchanged Pd2+ ion in mordenite under hydrothermal conditions by means of in situ UV-visible spectrometer, it was elucidated that Pd2+ ions sited in side pockets are more stable than those in main channels of mordenite. (c) 2005 Elsevier Inc. All rights reserved.

The undesired structural change of mordenite with Si/Al-2 = 15 during the ion exchange and during calcination from the sodium form into proton form, especially the dealumination after the calcination, was studied. The Si-29 NMR results clarified that calcination of the NH4-form mordenite with Si/Al-2 = 15 at > ca. 800 K, followed by the contact of proton-form sample with the atmosphere containing humidity, induced the dealumination. However, the samples carefully kept free from humidity after the heat treatment showed no dealumination or only a low degree of it. The Al-27 NMR and ammonia TPD results agreed with these findings. The origin of dealumination is thus considered to be the contact of the proton-form sample with humidity after the calcination. On the other hand, the dealumination was not observed after calcination at < 673 K. The H-1 NMR indicated that the ca. 1/3 of the ion-exchange sites were blocked by the ammonium cations after calcination at 673 K, suggesting that the dealumination was prevented by the ammonium cations. On the basis of these findings, a standard set of conditions in which one can safely prepare the proton-form zeolite with high quality is proposed. The recommended temperature for the ion exchange is room temperature, because it is high enough to exchange the ions in this case. The most important variable is the calcination temperature; it should be lower than 673 K in order to avoid the dealumination. These conditions were confirmed to yield zeolites with a high framework aluminum content and ordinary catalytic performance. (c) 2005 Elsevier B.V. All rights reserved.

Desulfurization of pipeline natural gas fuel at ambient conditions before introduction to reforming processes is strongly needed for stationary applications of fuel cells. Adsorptive removal of dimethlysulfide (DMS) and t-butylmercaptan (TBM) from pipeline natural gas was efficiently carried out by using silver exchanged Y zeolites (AgNa-Y) in the presence of water at room temperature and normal pressure. The capacity and adsorptivity for DMS and TBM on AgNa-Y were improved by an increase in silver content of AgNa-Y. Adsorption runs for DMS and TBM were carried out separately to compare their adsorptivity on AgNa-Y The sulfur adsorption capacity for DMS on Ag(18)Na-Y (1.9 mmol g(-1)) was much higher than that for TBM (0.6 mmol g(-1)). The clear color change of AgNa-Y during the period of adsorption run provides information regarding the formation of silver sulfide species on AgNa-Y The used AgNa-Y was regenerated easily by heat treatment in air at 500 degreesC. (C) 2004 Elsevier B.V. All rights reserved.

Effect of addition of H-2 on SCR of NO by C3H8 below 673 K was studied over various types of Ag-containing zeolites (MOR, MFI, BEA and Y). By the addition of 0.5% H-2, NO conversion below 673 K was increased on Ag-MFI and Ag-BEA, while it was not on Ag-MOR and Ag-Y. The dependence of NO conversion on H, concentration also differed greatly by zeolite types. The C3H8-SCR activity was enhanced by the addition of H-2 in the following order; Ag-MFI > Ag-BEA > Ag-MOR much greater than Ag-Y. The increment of NO conversion on Ag-MFI by the addition of H, became large with an increase in Si/Al ratio of MFI. UV-Vis spectroscopic study exhibited that the state of Ag species differed by zeolite types. From comparison between the C3H8-SCR activity and UV-Vis spectra, it is confirmed that moderately agglomerated Ag-n(delta+) cluster (2 less than or equal to n less than or equal to 4) is highly active species for NO reduction independently on zeolite types except Ag-Y. Balance of Ag species that governed the C3H8-SCR activity was shifted to more cationic Ag side with an increase of Si/Al ratio and in the order of acid strength (MOR > MFI > BEA). It is suggested that oxidative dispersion of agglomerated Ag species is accelerated by the increase in acid amount and strength. Control of the balance of Ag species by acid amount and strength would be a novel concept for design of Ag catalysts that exhibit high HC-SCR activity. (C) 2004 Elsevier B.V. All rights reserved.

The detailed structure of Ag Clusters formed in H zeolites during H-2 reduction as well as under NO + C3H8 + O-2 + H-2 reaction condition is examined with H-2-TPR, XRD, UV-vis, and Ag K-edge XAFS. H-2-TPR results suggest a quantitative conversion of the exchanged Ag+ ion to Ag-2p(p+) cluster in Ag-MFI during, H-2 reduction in a temperature range from 373 to 573 K. Combined with the UV-vis spectrum of the . UV-vis and cluster, exhibiting bands at 255 and 305 nm, and Ag K-edge EXAFS result, the structure of the cluster is identified as Ag-4(2+). UV-vis and K-edge XANES/EXAFS results reveal that, during NO + C3H8 + O-2 + H-2 reaction at 573 K, part of the Ag+ ions are converte Ag-n(delta+) clusters, whose average Structure can be close to Ag-4(2+). The amount of the clusters increases with the Ag/Al ratio of Ag zeolites. The NO reduction rate of Ag-MFI for the NO + C3H8 + O-2 reaction is significantly improved by an addition of 0.5% H-2, and the rate increases with Ag/Al ratio of Ag-MFI. This Cluster does not form on Ag-MOR under the same conditions, and the NO reduction rate does not increase by H-2 addition. The structure-activity relationship shows that the Ag-n(delta+) probably the Ag-4(2+) Cluster, in Ag-MFI catalysts is responsible for the selective reduction of NO by C3H8. (C) 2004 Elsevier Inc. All rights reserved.

The effect of H-2 on the selective reduction of NO by light hydrocarbons over Ag/Al2O3 catalyst under lean-exhaust conditions was investigated. The NO reduction activity at the low temperature region was markedly increased by adding H-2. The NO reduction activity at high GHSV condition and SO2 tolerance were also improved by adding H-2. Since the NO was reduced little by H-2 in the absence Of C-3 H-8, H-2 should act as a promoter of NO reduction by hydrocarbons over Ag/Al2O3 The results of reaction studies and in situ IR experiments showed that the possible reasons for promoting the effect by H-2 on the HC-SCR were mainly caused by the activation of hydrocarbons. (C) 2002 Elsevier Science B.V. All rights reserved.

The mechanistic cause of enhancement of C3H8-SCR activity by addition of H-2 over Ag/Al2O3 was investigated with in-situ FT-IR spectroscopy. Under a flow of NO + C3H8 + O-2, nitrates were mainly formed on Ag/Al2O3. An addition of H-2 into a C3H8-SCR atmosphere increased the concentration of surface acetate significantly, but decreased the concentration of surface nitrates. Formation and consumption rates of acetate and nitrates were estimated with transient in-situ IR measurement. By the addition of H-2, both formation rates of acetate and nitrates were increased. Moreover, both consumption rates of nitrates in a flow of C3H8 + O-2 and acetate in a flow of NO + O-2 were also increased by the addition of H-2. From a comparison between the evolutions of adsorbed species (nitrate and acetate) and gaseous species (NO and C3H8), it was clarified that the NO reduction activity is controlled by partial oxidation of C3H8 to mainly surface acetate. The addition of H-2 results in remarkable promotion of partial oxidation of C3H8 to mainly surface acetate, which is the rate-determining step of C3H8-SCR in the absence of H-2.

The effect of SO2 for the selective reduction of NO by C3H8 on Ag/Al2O3 was investigated in the presence of excess oxygen and water vapor. The NOx conversion decreased permanently even in the presence of a low concentration of SO2 (0.5-10 ppm) at <773 K. The increase in SO2 concentration resulted in a large decrease in NOx conversion at 773 K. However, when the reaction temperature was more than 823 K, the activity of Ag/Al2O3 remained constant even in the presence of 10 ppm of SO2. The sulfate species formed on silver should mainly decrease the deNO(x) activity on the Ag/Al2O3. The sulfated Ag/Al2O3 was appreciably regenerated by thermal treatment in the deNO(x) feed at 873 K. The moderate activity remains at 773 K in the presence of 1 ppm SO2 for long time by the heat treatment at every 20 h intervals. (C) 2001 Elsevier Science B.V. All rights reserved.

We examine the effect of H-2 on the selective reduction of NO by C3H8 over Ag/Al2O3 catalysts under lean-exhaust conditions. The NO reduction activity caused by C3H8 at low temperature (590-760 K) is greatly increased by adding H-2 in the presence of excess oxygen and water vapor.

Nitrogen oxides (NO(x)) contained in the exhaust gases from lean-burn natural-gas-fueled engines was removed by using an alumina supported silver (Ag/Al(2)O(3)) catalyst without addition of reducing agents. The NO(x) was efficiently reduced by unburned hydrocarbons contained in the exhaust gases over the 2 wt% Ag/Al(2)O(3) catalyst. The activity and durability of the 2 wt% Ag/Al(2)O(3) catalyst were demonstrated by using the exhaust gas from a 400 kW class lean-burn natural-gas-fueled engine for more than 2500 h.

A single phase (K, Na)-clinoptilolite was hydrothermally crystallized without seed crystals from a reactant mixture of(K, Na)-aluminosilicate gel slurry through homogeneous mixing at 150 degrees C for 144 h. Compositions of the reactant mixtures and reaction temperatures to obtain the clinoptilolite were restricted within narrow limits in the case of syntheses without seed crystals, while the compositions and temperatures were expanded into wide ranges in the case of syntheses with 1 wt.-% of seed crystals. Coexistence of Na+- and K+-ions with appropriate ratios in the reactant mixture, and homogeneous mixing of this mixture, were indispensable for the crystallization of clinoptilolite. The crystals obtained were characterized by X-ray diffraction, chemical analysis, thermal analysis (DTA/TG), electron microscopy, and electron diffraction. The crystals were assigned as clinoptilolite, not heulandite, based on their chemical compositions and thermal stability.

Intercalation property was investigated by insertion of dimethyl sulfoxide and its removal for four types of synthesized kaolinite samples. All the synthetic kaolinites with platy morphology formed intercalation compounds with different ratios and rates. The intercalation with the well-crystallized synthetic kaolinite was completed. However, the intercalation ratios and rates were independent of the degree of stacking disorder of the synthetic kaolinites. On the other hand, no intercalation compound was formed with the spherical synthetic kaolinite.