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ABSTRACT: A study has been undertaken on the thermal stability and dispersion behavior of nanostructured CexZr1−xO2 mixed oxides over anatase-TiO2 support, synthesized by a deposition coprecipitation method and subjected to heat treatments at different temperatures. An unsupported CexZr1−xO2 mixed oxide was also synthesized by coprecipitation method for the purpose of comparison. The structural/morphological characterization was performed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS), UV−visible diffuse reflectance spectroscopy (UV−vis DRS), and temperature-programmed reduction (TPR) techniques. XRD measurements revealed the presence of cubic Ce0.75Zr0.25O2 phase at 773 K and incorporation of more zirconium into the ceria lattice at higher temperatures. HREM analysis conformed highly dispersed Ce−Zr nano-oxides over anatase-TiO2 support having the sizes in the range of 3−5 nm at 773 K. At higher temperatures, a slight increase in the crystallite size (5−10 nm) has been observed. The XPS measurements revealed the stabilization of Ce3+ at higher temperatures and presence of Zr and Ti in 4+ oxidation states. UV−vis DRS studies showed that oxygen to metal (Ce4+/Ce3+) charge-transfer transitions occur at lower wavelengths in the case of CexZr1−xO2/TiO2 compared to pure CexZr1−xO2. TPR experiments revealed that the surface reduction of CexZr1−xO2/TiO2 takes place at lower temperatures, which facilitates better CO oxidation activity in comparison to the unsupported CexZr1−xO2.
11/2008;
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ABSTRACT: Structural characteristics and catalytic activity of nanosized ceria−terbia mixed oxides have been investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy, temperature-programmed reduction/oxidation, and Brunauer−Emmett−Teller surface area techniques. The catalytic usefulness has been evaluated for oxygen storage-release capacity (OSC) and CO oxidation activity. The XRD and TEM results suggest that the crystallite sizes of these nano-oxides are in the range 5−12 nm within the investigated temperature range of 773−1073 K. The mixed oxide solid solutions adopted a fluorite-type structure and exhibited cell parameters with respect to Vegard’s rule. The XPS measurements revealed that both cerium and terbium are in 3+ and 4+ oxidation states, 4+ being dominant in both cases. The reduction temperature of the Ce−Tb oxide is observed to be lower than that of the pure ceria and exhibited better redox properties due to the formation of solid solution. The OSC is substantially higher for the mixed oxide, and the presence of oxygen vacancies favored better CO oxidation activity. The nanosized ceria−terbia mixed oxide is also found to be thermally quite stable and capable of manifesting redox behavior after severe heat treatment.
09/2008;
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ABSTRACT: The crystal structures, electronic, dielectric, and vibrational properties of NaH, Na(2)O and NaOH are systematically investigated by first-principles calculations and the quasiharmonic approximation. The phonon dispersion relations and the phonon density of states of the phases and their thermodynamic functions including the heat capacity, the vibrational enthalpy, and the vibrational entropy are calculated using a direct force-constant method. Based on these results, the dehydrogenation reaction, NaH+NaOH-->H(2)+Na(2)O, is predicted to take place at 528 K, which is in agreement with the experimental observed value.
ChemPhysChem 09/2007; 8(13):1979-87. · 3.41 Impact Factor
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ABSTRACT: The adsorption and dissociation of H2 on the Na2O (110) surface have been studied with the first-principles molecular dynamics method. It is found that the adsorption configuration is energetically preferred when the H2 molecule is situated at the bridge site of the Na and O atoms, which indicates the formation of a Na−Hδ-···Hδ‘+−O dihydrogen bond, as confirmed by the charge distribution features and bond lengths between the concerned atoms. The molecular dynamics simulations reveal the dissociation of the newly discovered H···H dihydrogen bond, which facilitates the Na2O + H2 → NaH + NaOH reaction.
03/2007;
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Angewandte Chemie International Edition 02/2007; 46(42):8024-7. · 13.45 Impact Factor
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Angewandte Chemie International Edition 06/2006; 45(19):3120-2. · 13.45 Impact Factor
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ABSTRACT: The thermal stability of a nanosized Ce(x)Zr(1-x)O2 solid solution on a silica surface and the dispersion behavior of V2O5 over Ce(x)Zr(1-x)O2/SiO2 have been investigated using XRD, Raman spectroscopy, XPS, HREM, and BET surface area techniques. Oxidative dehydrogenation of ethylbenzene to styrene was performed as a test reaction to assess the usefulness of the VOx/Ce(x)Zr(1-x)O2/SiO2 catalyst. Ce(x)Zr(1-x)O2/SiO2 (1:1:2 mol ratio based on oxides) was synthesized through a soft-chemical route from ultrahigh dilute solutions by adopting a deposition coprecipitation technique. A theoretical monolayer equivalent to 10 wt % V2O5 was impregnated over the calcined Ce(x)Zr(1-x)O2/SiO2 sample (773 K) by an aqueous wet impregnation technique. The prepared V2O5/Ce(x)Zr(1-x)O2/SiO2 sample was subjected to thermal treatments from 773 to 1073 K. The XRD measurements indicate the presence of cubic Ce0.75Zr0.25O2 in the case of Ce(x)Zr(1-x)O2/SiO2, while cubic Ce0.5Zr0.5O2 and tetragonal Ce0.16Zr0.84O2 in the case of V2O5/Ce(x)Zr(1-x)O2/SiO2 when calcined at various temperatures. Dispersed vanadium oxide induces more incorporation of zirconium into the ceria lattice, thereby decreasing its lattice size and also accelerating the crystallization of Ce-Zr-O solid solutions at higher calcination temperatures. Further, it interacts selectively with the ceria portion of the composite oxide to form CeVO4. The RS measurements provide good evidence about the dispersed form of vanadium oxide and the CeVO4 compound. The HREM studies show the presence of small Ce-Zr-oxide particles of approximately 5 nm size over the surface of amorphous silica and corroborate with the results obtained from other techniques. The catalytic activity studies reveal the ability of vanadium oxide supported on Ce(x)Zr(1-x)O2/SiO2 to efficiently catalyze the ODH of ethylbenzene at normal atmospheric pressure. The remarkable ability of Ce(x)Zr(1-x)O2 to prevent the deactivation of supported vanadium oxide leading to stable activity in the time-on-stream experiments and high selectivity to styrene are other important observations.
The Journal of Physical Chemistry B 06/2006; 110(18):9140-7. · 3.70 Impact Factor
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ABSTRACT: The thermal stability of a nanosized CexZr1-xO2 solid solution on a silica surface and the dispersion behavior of V2O5 over CexZr1-xO2/SiO2 have been investigated using XRD, Raman spectroscopy, XPS, HREM, and BET surface area techniques. Oxidative dehydrogenation of ethylbenzene to styrene was performed as a test reaction to assess the usefulness of the VOx/CexZr1-xO2/SiO2 catalyst. CexZr1-xO2/SiO2 (1:1:2 mol ratio based on oxides) was synthesized through a soft-chemical route from ultrahigh dilute solutions by adopting a deposition coprecipitation technique. A theoretical monolayer equivalent to 10 wt % V2O5 was impregnated over the calcined CexZr1-xO2/SiO2 sample (773 K) by an aqueous wet impregnation technique. The prepared V2O5/CexZr1-xO2/SiO2 sample was subjected to thermal treatments from 773 to 1073 K. The XRD measurements indicate the presence of cubic Ce0.75Zr0.25O2 in the case of CexZr1-xO2/SiO2, while cubic Ce0.5Zr0.5O2 and tetragonal Ce0.16Zr0.84O2 in the case of V2O5/CexZr1-xO2/SiO2 when calcined at various temperatures. Dispersed vanadium oxide induces more incorporation of zirconium into the ceria lattice, thereby decreasing its lattice size and also accelerating the crystallization of Ce−Zr−O solid solutions at higher calcination temperatures. Further, it interacts selectively with the ceria portion of the composite oxide to form CeVO4. The RS measurements provide good evidence about the dispersed form of vanadium oxide and the CeVO4 compound. The HREM studies show the presence of small Ce-Zr-oxide particles of 5 nm size over the surface of amorphous silica and corroborate with the results obtained from other techniques. The catalytic activity studies reveal the ability of vanadium oxide supported on CexZr1-xO2/SiO2 to efficiently catalyze the ODH of ethylbenzene at normal atmospheric pressure. The remarkable ability of CexZr1-xO2 to prevent the deactivation of supported vanadium oxide leading to stable activity in the time-on-stream experiments and high selectivity to styrene are other important observations.
04/2006;
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07/2005: pages 189 - 209; , ISBN: 9783527604104
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ABSTRACT: Instruments for the preparation of heterogeneous catalysts in powder form have been developed. The instruments consist of powder dispensing robot and an automated liquid handling machine equipped with an ultrasonic and a vortex mixer. The combination of these two instruments achieves the catalyst preparation by incipient wetness and ion exchange methods. The catalyst library prepared with these instruments were tested for dimethyl ether steam reforming and characterized by transmission electron microscopy observations.
Review of Scientific Instruments 06/2005; 76(6):062226-062226-4. · 1.37 Impact Factor
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ABSTRACT: Alumina–zirconia mixed oxide-supported sulfate-, molybdate-and tungstate-promoted solid acid catalysts were synthesized and charac-terized by various techniques. The Al–Zr hydroxide gel was obtained by a co-precipitation method from their corresponding nitrate salts by hydrolysis with aqueous ammonia. To the Al–Zr-hydrous mixed oxide support, aqueous solutions of sulfuric acid, ammonium heptamolybdate and ammonium metatungstate were added and the mixtures were refluxed at 110 • C, followed by evaporation of the water, drying and calcina-tion at 650–750 • C. The surface and bulk properties of the catalysts were examined by using X-ray diffraction, BET surface area, TGA/DTA, ammonia-TPD and XPS techniques. The XRD results reveal that Al 2 O 3 –ZrO 2 mixed oxide calcined at 650 • C is in amorphous or poorly crystalline state exhibiting broad diffraction lines due to tetragonal ZrO 2 phase. At 750 • C calcination, a better crystallization of the zirconia tetragonal phase is observed. The XRD results further indicate that incorporation of alumina into zirconia stabilizes the tetragonal phase. The TGA–DTA studies provide information that there are at least two types of sulfate species with different thermal stabilities in the case of SO 4 2− /Al 2 O 3 –ZrO 2 catalyst. The TPD study reveals that the SO 4 2− /Al 2 O 3 –ZrO 2 catalyst exhibits an ammonia desorption peak maximum at 600 • C indicating super-acidic nature of the catalyst. The XPS peak intensities and the corresponding binding energies indicate that sulfate ion interacts with the support more strongly than other promoters. All characterization results provide information that the impregnated sulfate ions show a relatively strong influence on the physicochemical properties of the Al 2 O 3 –ZrO 2 mixed oxide. The prepared catalysts were evaluated for acetylation of alcohols and amines with acetic anhydride in the liquid phase. In line with physicochemical characteristics, the SO 4 2− /Al 2 O 3 –ZrO 2 exhibits better product yields under very mild reaction conditions.
Journal of Molecular Catalysis A Chemical 01/2005; 227:81-89. · 2.95 Impact Factor
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ABSTRACT: We used a semiconductor gas sensor system developed for odour discrimination for a rapid quantification of benzene derivatives which can be formed as the product of a catalytic reaction. Phenol can be obtained by the selective oxidation of benzene. The sensor system shows higher sensitivity to phenol than benzene. In particular, a SnO2 sensor sensitized with ZrO2 responds selectively to phenol. Aniline is provided as a reaction product between ammonia and benzene. The output signal of the gas sensor system increases when it is exposed to air containing aniline at the ppm level; on the other hand, the sensor output resulting from 1% ammonia in air does not increase so much. Cumene formation can be observed by the reaction of propane and benzene. The sensitivity of a SnO2 sensor sensitized with 12%SiO2–Al2O3 to cumene was about ten times higher than that to benzene. These results indicate that the semiconductor gas sensor system is useful for rapid screening of the catalyst for benzene functionalization.
Measurement Science and Technology 12/2004; 16(1):229. · 1.49 Impact Factor
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ABSTRACT: Hydrazine was examined as a fuel in a direct-liquid-fueled fuel cell that uses proton exchange membrane (PEM) such as Nafion ® . Different kinds of noble metals were examined as anode electrocatalysts for direct hydrazine fuel cells (DHFCs). In DHFC using platinum or palladium as the anode electrocatalyst, more than 1 V of cell voltage was obtained in the low-current density region. The I–V characteristics changed drastically depending on the kind of anode electrocatalyst used. Compositions of the exhaust materials from each electrode were analyzed to investigate the reaction occurring at the electrodes. The analysis revealed that the catalytic decomposition reaction of hydrazine proceeded further than the electro-oxidation reaction on the anode side using rhodium or ruthenium.
Journal of Power Sources 01/2003; 122:132-137. · 4.95 Impact Factor
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Yusuke Yamada,
Atsushi Ueda,
Hiroshi Shioyama,
Thomas Mathew,
Tsutomu Ioroi,
Kazuaki Yasuda,
Tomoki Akita,
Satoshi Ichikawa,
Koji Tanaka,
Masanori Kohyama, Tetsuhiko Kobayashi
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ABSTRACT: Our efforts to combine the combinatorial technology and microstructure analysis to develop catalysts for proton exchange membrane fuel cell (PEMFC) technology have been described. This offers the realization of “materiomics” in comprehensive material research. Catalyst technologies are indispensable for wide use of PEMFC, which are regarded as the low emission and highly efficient energy conversion device for the next generation. We have applied the combinatorial method for the hydrogen production and/or purification of catalysts, and anode catalyst investigations. The catalyst library consisting of precious metals loaded on various metal oxides was tested for water gas shift reaction and steam reforming of methanol and/or DME. Various metal oxides added to platinum loaded on carbon were screened for anode catalysts. The microstructure of each catalyst was analyzed by employing scanning electron and/or transmission electron microscopy. This paper mainly describes the catalysis screening results of above reactions that form a part of “materiomics”.
MRS Proceedings. 12/2002; 804.
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ABSTRACT: A significant yield of aldehydes was obtained by the partial oxidation of ethane over alkali‐modified Fe/SiO2 catalysts at 475°C (<2% in the case of Cs–Fe/SiO2). Not only acetaldehyde and formaldehyde but also acrolein were produced in the present system. There are no reports regarding
the catalysts for the direct acrolein formation from partial oxidation of ethane. Such significant promoting effect of alkali‐modified
Fe/SiO2 catalysts in the partial oxidation of hydrocarbons has never been observed. Aldol‐type condensation for formation of acrolein
could occur in the partial oxidation of ethane over alkali‐modified Fe/SiO2 catalysts.
Catalysis Letters 10/1999; 63(1):79-82. · 2.24 Impact Factor
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ABSTRACT: Supporting Pt and Pd catalysts have been examined for the reduction of NO with H2 in the presence of oxygen and moisture. All catalysts showed a conversion maximum in the NO reduction at around 373 K. An additional conversion maximum was found to appear at around 573 K over several metal oxides supporting Pd, and Pd/TiO2 gave the highest conversion at around 573 K among the catalysts tested. In the reaction at 373 K, NO might be reduced directly by H2 both on Pt and Pd catalysts to give N2 and N2O. At the conversion maximum of the Pd/TiO2 catalyst at 575 K, however, in situ generated NO2 seems to react with H2.
Catalysis Today 45:135-138. · 3.41 Impact Factor
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ABSTRACT: The steam reforming of dimethyl ether (DME) was performed on Cu/GaxAl10 − xO15 and GaxAl10 − xO15 catalysts (where ‘x’ varies from 0 to 10). The presence of Ga2O3 in Al2O3 significantly affects the catalytic performance with respect to the DME conversion and the H2 yield. It was found that the activity increases with the Ga2O3 concentration for GaxAl10 − xO15. The DME steam reforming activity on Cu/GaxAl10 − xO15 showed an improvement in the stability and H2 yield as the Ga2O3 concentration increased. A correlation between the XPS results and the DME steam reforming activity for Cu/GaxAl10 − xO15 reveals that the heterogeneity of the surface is important for achieving a high H2 yield. The specific interaction between Ga2O3 and Cu plays a decisive role in the distribution of Cu, which makes Cu/GaxAl10 − xO15 active and stable for the reaction.
Applied Catalysis A: General. 286(1):11-22.
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ABSTRACT: Many samples containing different elements M in the system of M/SiO2 (M : Si = 1 : 1000, molar ratio) or Cs/M/SiO2 (Cs : M : Si = 10 : 1 : 1000, molar ratio) were prepared and screened for the oxidation of ethane by use of oxygen as oxidant. It has been found that the elements M (M = V, Bi, In, Ga, P, Zr, Zn, La) can give good aldehyde yields in the Cs/M/SiO2 system. The promoting effects of different alkali metals (Li, Na, K, Rb, Cs) on the catalytic performance of V/SiO2 (V : Si = 1 : 1000) in ethane oxidation were investigated. Among them, cesium gave the best promoting effect on V/SiO2 for aldehyde formation. The presence of alkali metals increases the basicity and neutralizes the acid site of catalyst; thus it enhances the selectivity to acetaldehyde and controls the formation of formaldehyde. Increase in basicity promotes the cross-aldol condensation of acetaldehyde and formaldehyde to give acrolein. The pathway for acrolein formation is mainly through the cross-aldol condensation of acetaldehyde and formaldehyde over Cs/V/SiO2 catalysts.
Applied Catalysis A: General. 196(1):37-42.
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ABSTRACT: Nanocrystalline mesoporous TiO2-based catalysts prepared by a surfactant-assisted templating sol–gel process were tested on epoxidation of cyclohexene in tert-butanol–H2O2 system. The mesoporous TiO2 showed exceptional potential for epoxidation of cyclohexene, exhibiting both higher cyclohexene conversion and higher cyclohexene oxide selectivity than non-mesoporous commercial TiO2 powders, i.e. Ishihara ST-01 and Degussa P-25. The oxides of Fe, Co, Ni, and Ru were also loaded by incipient wetness impregnation method onto the synthesized mesoporous TiO2, aiming to enhance the catalytic performance. Among metal oxide-loaded catalysts, RuO2-loaded mesoporous TiO2 was proved to possess noticeably high catalytic performance based on cyclohexene oxide selectivity. The 1 mol% RuO2-loaded mesoporous TiO2 was the best catalyst, showing the highest cyclohexene oxide selectivity and lowest cyclohex-2-en-1-ol (undesired product) selectivity. Plausible reaction pathways were also proposed.Graphical abstractNanocrystalline mesoporous TiO2 with narrow and monomodal pore size distribution prepared by surfactant-assisted templating sol–gel process of laurylamine hydrochloride/tetraisopropyl orthotitanate modified with acetylacetone system exhibits higher catalytic cyclohexene epoxidation activity than non-mesoporous commercial TiO2 powders.
Journal of Molecular Catalysis A Chemical 241:23-32. · 2.95 Impact Factor
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ABSTRACT: The oxidation of ethane by oxygen was studied over silica catalysts supporting different amounts of vanadium with and without cesium. Three different catalytic properties of the product selectivity were observed, aldehyde formation, oxidative dehydrogenation (ODH), and combustion, depending upon the vanadium loading amount and the presence or the absence of cesium. A very low loading of vanadium (V:Si=0.02–0.1 at.%) and the addition of Cs (Cs:Si=1 at.%) on silica were found to be important for the formation of aldehyde. Not only acetaldehyde but also acrolein were observed in the aldehyde formation from ethane. On the other hand, catalysts with medium and high vanadium loadings (V:Si=0.5–20 at.%) gave a dehydrogenated product, ethene, when Cs was not added to the catalysts. The addition of cesium to the catalysts with medium and high vanadium loadings changed the catalytic property from ODH to combustion. The different types of vanadyl species were identified by UV–visible and IR measurements in samples with different vanadium loadings. It was estimated that isolated vanadyl species with tetrahedral coordination, which were found mainly on the catalysts with vanadium loading lower than 0.5 at.%, became the active site for the aldehyde formation through the interaction with Cs. As a plausible reaction path giving acrolein from ethane, cesium-catalyzed cross-condensation between acetaldehyde and formaldehyde, formed in the reaction, was proposed. Polymeric vanadyl species with octahedral coordination and vanadium–oxygen clusters with dioxo tetrahedral coordination were detected in the samples with medium (0.5–5.0 at.%) and high (10 and 20 at.%) vanadium loadings, respectively. Both species show the ODH catalytic property without cesium, but they bring about a deep oxidation of ethane if cesium is added to the catalysts.
Journal of Catalysis. 190(2):215-227.
