Showing papers on "Mixed oxide published in 2004"
TL;DR: In this paper, spc-Ni/MgAl catalysts were used for the partial oxidation of CH 4 into synthesis gas, and the surface area of spcNi 0.5 /Mg 2.5 Al catalysts was around 150m 2 ǫg cat −1.
310 citations
TL;DR: In this paper, the results showed that an Al-Mg mixed oxide with an Al/(Al+Mg) molar ratio of 0.25 with a water content of 35 wt% was the optimum catalyst for the Claisen-Schmidt condensation between benzaldehyde and acetophenone.
219 citations
TL;DR: In this article, high specific surface areas (77-244m 2 /g) were obtained for Titania-zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 ¼ ) by the sol-gel method.
Abstract: Titania–zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 wt.%) were prepared by the sol–gel method. High specific surface areas (77–244 m 2 /g) were obtained. Acidity determined by NH 3 -TPD and FTIR-pyridine adsorption showed that in mixed oxides the number of acid sites is dramatically increased; it varies from 173 μmol NH 3 /g for TiO 2 to 1226–1456 μmol NH 3 /g for the mixed oxides. FTIR-pyridine adsorption showed the presence of Lewis sites in the catalysts. Basic sites were identified by FTIR-CO 2 adsorption, suggesting the formation of mixed oxides with acid–basic properties. XRD spectra identified anatase in the TiO 2 rich region, amorphous material in the mixed oxide 50–50 TiO 2 –ZrO 2 and tetragonal and monoclinic crystalline phases in the ZrO 2 rich region. Activity in the isopropanol decomposition showed a good correlation between the acid–basic properties and the selectivity to propene, acetone and isopropyl ether. The latter was found as a product which mainly depends of the acid sites density.
210 citations
TL;DR: In this article, the optimum performance in electrocatalytic activity for oxygen evolution reaction in alkaline media was obtained on the Co+Ni mixed oxide deposited from the solution containing Co{sup 2+}/Ni{sup2+} ratio of 1:1.
164 citations
TL;DR: In this paper, it was shown that substituting Ti atoms for Si in a silica thin film network leads to a marked increase in the cluster number density compared to the Ti-free SiO.
Abstract: Following the discovery that small gold clusters highly dispersed on metal oxide supports are active catalysts at low temperature for a variety of reactions, a number of studies have been carried out to determine the structure of the clusters and the mechanism leading to their activity. A major deterrent to the use of these catalysts, however, is that under reaction temperatures and pressures, the clusters tend to sinter, or agglomerate, leading to a dramatic decrease in activity. In an attempt to make these highly active Au catalysts more stable, mixed-oxide supports have been developed by substituting Ti atoms for Si in a silica thin film network. Depending on the amount of Ti deposited, the TiO2−SiO2 surface consists of substituted Ti atoms and/or TiOx islands. With deposition of Au onto these TiO2−SiO2 surfaces (at low and high Ti coverages), the substituted Ti and/or TiOx islands act as Au cluster nucleation sites, leading to a marked increase in the cluster number density compared to the Ti-free SiO...
119 citations
TL;DR: In this article, two different synthesis routes were applied to prepare TiO2-XSiO2 (X denotes mol% of silica in titania-silica mixed oxides) with different silica concentrations by using ammonia water as hydrolysis catalyst.
Abstract: Two different synthesis routes were applied to prepare TiO2–XSiO2 (X denotes mol% of silica in titania–silica mixed oxides) with different silica concentrations by using ammonia water as hydrolysis catalyst. Through comparing the photocatalytic performance of two sets of mixed oxides, we found that the photocatalytic activity of mixed oxides prepared via the route which can promote homogeneity, was significantly enhanced as compared with that of counterparts prepared via the another route, and the highest photocatalytic activity obtained by adding about 9.1 mol% silica into titania was much higher than that of pure TiO2. The mixed oxides were investigated by means of XRD, thermal analysis, UV–vis, FT-IR and XPS. The characterization results suggest that, in comparison with pure TiO2, the mixed oxides exhibit smaller crystallite size and higher thermal stability which can elevate the temperature of anatase to rutile phase transformation due to the addition of silica. Furthermore, Bronsted acidity, which is associated with the formation of Ti O Si hetero linkages where tetrahedrally coordinated silica is chemically mixed with the octahedral titania matrix, may be a very important contribution to the enhanced photocatalytic activity of titania–silica mixed oxides as well.
112 citations
TL;DR: In this paper, the selective surface modification by phosphonic acids of SiO2−TiO2 supports at the micrometer and molecular scale was investigated under aqueous conditions.
Abstract: The selective surface modification by phosphonic acids of SiO2−TiO2 supports at the micrometer and molecular scale was investigated. Under aqueous conditions, phosphonic acids bind to TiO2 and not to SiO2 surfaces. A micropatterned support was prepared by electron beam microlithography and selectivity, of the surface modification was evidenced using scanning Auger electron spectroscopy (SAES). The second support was a mesoporous SiO2−TiO2 mixed oxide (10 mol % Ti) epoxidation catalyst prepared by sol−gel processing. Selectivity was deduced from the decrease of the catalytic activity upon modification and from chemical analysis; bonding modes to the surface were investigated using solid-state 29Si and 31P MAS NMR. The possibility to introduce different organic groups by successive treatments with a phosphonic acid and a silylating agent was illustrated in the case of the mixed oxide.
111 citations
TL;DR: In this article, a series of CexZr1−xO2 catalysts with 1.5% Pd were exposed to fixed exposures of SO2 under oxidizing environments and then characterized by FTIR, pulse-reactor studies with CO and O2, and temperature-programmed desorption (TPD).
Abstract: CeO2, ZrO2, and a series of CexZr1−xO2 catalysts with 1 wt.% Pd were exposed to fixed exposures of SO2 under oxidizing environments and then characterized by FTIR, pulse–reactor studies with CO and O2, and temperature-programmed desorption (TPD). For exposures above 473 K, sulfates were formed on all of the materials; however, the results are consistent with the formation of bulk sulfates on CeO2 and only surface sulfates on ZrO2. For the mixed oxides, the quantity of sulfates formed at 673 K increased linearly with the Ce content. In TPD, the sulfates on ZrO2 were stable to higher temperatures than those formed on CeO2, which decomposed in a well-defined peak between 900 and 1050 K. The sulfates on both oxides were reduced by CO above 750 K. Even though XRD patterns for the mixed oxide were significantly different from that of the physical mixture, the TPD and pulse–reactor results were similar to what would be expected for physical mixtures of CeO2 and ZrO2, suggesting that sulfate species are associated with individual metal cations. Finally, pulse–reactor studies with CO and O2 at 873 K show that the sulfates can be reversibly reduced and oxidized on both CeO2 and ZrO2, so that sulfur poisoning gives rise to an apparent increase in oxygen storage, demonstrating that this method is not acceptable for measurement of this quantity.
107 citations
TL;DR: In this article, the authors showed that the catalysts prepared by impregnation method are more active than those prepared by gel impregnation method because of their higher degrees of metal dispersion and reducibility.
104 citations
TL;DR: In this article, the platinum dispersion has been determined by chemisorption of H 2 and CO on a series of ceria-zirconia supported catalysts.
Abstract: The platinum dispersion has been determined by chemisorption of H 2 and CO on a series of ceria–zirconia supported catalysts covering the full range of composition between ceria and zirconia. The quantities were measured by volumetric techniques and by FTIR spectroscopy. Reduction and measurement temperatures were studied in order to fix a specific H 2 chemisorption protocol. The latter is based on the use of double isotherm of hydrogen adsorption at 195 K, this low temperature being required to suppress the hydrogen spillover on the support. The irreversible adsorption measured either at saturation or by extrapolation to zero pressure leads to the most reliable dispersion values, in agreement with those deduced from CO chemisorption at room temperature followed by FTIR spectroscopy, technique which allows to discriminate the adsorption on the platinum surface from that on the ceria–zirconia support. By applying these two methods, it was found that, after reduction at 473 K, platinum dispersion is always higher on the mixed oxides than on the pure ceria or zirconia supports. It was nearly constant at 60–65% for a wide range of composition of the mixed oxide between Ce 0.15 Zr 0.85 and Ce 0.68 Zr 0.32 .
96 citations
TL;DR: In this paper, the authors reported the preparation of mixed oxides of different composition, incorporating the biopolymer chitosan to the precursor mixed sol, producing a hybrid xerogel.
TL;DR: In this paper, the complete oxidation of chlorinated aliphatic hydrocarbons over CexZr1−xO2-based catalysts has been studied using a conventional fixed bed flow reactor.
Abstract: The complete oxidation of chlorinated aliphatic hydrocarbons, such as 1,2-dichloroethane, and trichloroethylene, over CexZr1−xO2-based catalysts has been studied using a conventional fixed bed flow reactor. The mixed oxide catalysts exhibited a higher activity with respect to the pure oxides, and catalytic conversion was found to depend on Ce/Zr molar content. Thus, Ce0.5Zr0.5O2 showed the highest combustion activity for the abatement of both chlorohydrocarbons. The combination of surface acidity and accessible lattice oxygen appeared to control the catalytic performance of the mixed oxides.
The major oxidation products were CO2, HCl and Cl2 along with trace amounts of other chlorinated by-products, namely vinyl chloride and tetrachloroethylene, and carbon monoxide. The selectivity toward CO2 and Cl2 was found to be noticeably promoted with increasing cerium content. Thus behaviour was related to the high activity of ceria in CO and HCl oxidation to give Cl2 by the Deacon reaction.
TL;DR: In this paper, it was shown that the synergy that operates between the titania and the alumina components involves the intrinsic surface chemistry of these oxides rather than formation of mixed oxide phases.
TL;DR: In this paper, three wet chemistry routes were used to synthesize Ba0.99Zr0.8Y0.2O3-delta (BZY20) and to avoid the drawbacks of the conventional mixed oxide route used for its preparation.
TL;DR: In this article, the authors combined partial oxidation and dry reforming of methane (PO-DRM) to synthesis gas at 850°C over noble metals, supported on Mg-Al mixed oxide, has been studied.
Abstract: Combined partial oxidation and dry reforming of methane (PO–DRM) to synthesis gas at 850 °C over noble metals, supported on Mg–Al mixed oxide, has been studied. Ruthenium, rhodium, and platinum catalysts were prepared from layered double hydroxide (LDH) precursors, synthesized by a reconstruction reaction of Mg–Al mixed oxide. Due to a “memory effect” of a calcined hydrotalcite, a layered structure of catalyst precursors was recreated upon exposure of the mixed oxide to an aqueous solution of noble metals, which were pre-chelated with ethylenediaminetetraacetate (EDTA) to anionic species. Among the three metals tested, ruthenium revealed the most attractive catalytic performance toward PO–DRM reaction. It was shown that amount of metal could be lowered from 2.0 to 0.1% of the weight of support without any decrease in catalytic activity or in selectivity to syngas product.
TL;DR: In this article, the performance of ZrO 2 -based catalysts was evaluated in the selective synthesis of isobutene and isobutanane (i-C 4 ) from CO hydrogenation at 673 K, 5.0 MPa, and 650 h −1.
TL;DR: In this article, the dissolution of Th 1� xUxO2 was investigated through leaching experiments combined with X-ray photoelectron spectroscopy (XPS) and XAS analyses.
TL;DR: The local structure and the photoactivity of B 2 O 3 -SiO 2 /TiO 2 ternary mixed oxides were investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement.
Abstract: The local structure and the photoactivity of B 2 O 3 –SiO 2 /TiO 2 ternary mixed oxides (SiO 2 content was fixed as 30 at.% with respect to TiO 2 ) was investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement. In FT-IR analysis, boron was incorporated into the framework of titania matrix with replacing TiOSi with SiOB or TiOB bonds. Also, paramagnetic species such as O − and Ti 3+ defects were formed by the boron incorporation. In SiO 2 /TiO 2 mixed oxides, a blue shift in the light absorption band was observed due to the quantization of band structure. All B 2 O 3 –SiO 2 /TiO 2 samples had pure anatase phase and no rutile phase was formed even though the calcination temperature was over 900 °C. Incorporating boron oxides of more than 10% enlarges the grain size of anatase phase and causes a red shift of the light absorption spectrum. The surface area was monotonically decreased with increasing the content of boron content. As a result, the photoactivity of B 2 O 3 –SiO 2 /TiO 2 ternary mixed oxides was greatly influenced by the content of boron oxide. The highest photoactivity (g moles/min l) was obtained when the boron content was 5% and seven times higher than that of silica/titania binary mixed oxide. In addition, the specific photoactivity (g moles/m 2 l) was maximum still at 5%. It was concluded that the large reduction of surface area, the change of band structure, and more formation of bulk Ti 3+ sites are responsible for the deterioration in the photoactivity of B 2 O 3 –SiO 2 /TiO 2 ternary mixed oxides when the content of boron is over 10%, although their crystallinity was enhanced by increasing the calcination temperature with keeping anatase phase.
TL;DR: In this article, the extent of BiInO3 substitution in the perovskite system xBiO3-PbTiO3 and the corresponding raise in the Curie temperature were investigated using thermal analysis, dielectric measurements, x-ray diffraction, and electron microscopy.
Abstract: The extent of BiInO3 substitution in the perovskite system xBiInO3–(1 - x)PbTiO3 and the corresponding raise in the Curie temperature were investigated using thermal analysis, dielectric measurements, x-ray diffraction, and electron microscopy. Maximum tetragonal perovskite distortion (c/a = 1.082) was obtained for x = 0.20, with a corresponding Curie temperature of 582 °C. Phase-pure tetragonal perovskite was obtained for x ⩽ 0.25. Compound formation after calcining mixed oxide powders resulted in agglomerated cube-shaped tetragonal perovskite particles, which could be fired to 94.7% of theoretical density (TD). Sol-gel fabrication resulted in nano-sized tetragonal or pseudo-cubic perovskite particles, which after two-step firing, resulted in a tetragonal perovskite microstructure at as high as (x = 0.20) 98.1% of TD.
TL;DR: In this article, Pd/Pt catalysts supported on a basic Mg/Al mixed oxide obtained by calcination of a commercial hydrotalcite (SASOL, D) have been fully characterized by XRD, SEM, and FTIR and investigated in the vapor-phase hydrogenation of naphthalene in order to put in evidence the role of the active phase and the acidity of the support on the hydrogenolysis/ring-opening reaction as well as the thio-tolerance of the catalysts.
TL;DR: In this article, the nanostructural and nanochemical changes occurring in pure ceria (CeO2) and CeO2-zirconia (ZrO2)) catalysts during reduction were studied.
Abstract: We have studied the nanostructural and nanochemical changes occurring in pure ceria (CeO2) and CeO2–zirconia (ZrO2) catalysts during reduction. The reduction is carried out in an environmental transmission electron microscope in dry H2 at 2 Torr up to 800°C. We use in-situ electron-energy-loss spectroscopy to follow changes in the oxidation state of the Ce at close to the nanometre level. Our measurements show that reduction may or may not be accompanied by significant structural rearrangements in the material. In pure CeO2 and the mixed oxide, the reduced form can be composed of both crystalline and amorphous material. Our measurements confirm the formation of a superlattice formed due to the ordering of O vacancies in CeO2 during reduction. The mixed oxide material shows that O vacancy ordering occurs only over 2–3 nm domains.
TL;DR: In this article, the presence of a chromate solid solution of the type La 0.8 Sr 0.2 Cr1-xMgx O 4 (x⩽0.2) as a low-temperature intermediate to perovskite-type is experimentally established using TG/DTA and XRD.
Abstract: Sr- and Mg-doped LaCrO3 nanosized powders were succesfully synthesized from a polymeric precursor solution containing the respective aqueous solution of metal nitrate, chromium (III) nitrate, nitric acid, and ethylene glycol. The presence of a chromate solid solution of the type La 0.8 Sr0.2 Cr1-xMgx O 4 (x⩽0.2) as a low-temperature intermediate to perovskite-type is experimentally established using TG/DTA and XRD. In Sr, Mg-substituted LaCrO3, single-phase perovskite La0.8Sr0.2Cr1-xMgx O3 was formed at about 770 °C by decomposition of the chromate phase solid solution, which crystallizes at about 520 °C from amorphous powders. La0.8Sr0.2Cr1-x Mgx O3 perovskite solid solution powders with surface areas as high as 11 m2/g and nanosized particles sintered at 1550 °C for 6 h in air were higher than 97% dense materials. Such an improvement in densification can be attributed to a two-stage shrinkage process, i.e., liquid phase formation and solid perovskite particle rearrangement in the liquid, respectively. No significant variations in both the final density and grain size with increasing Mg content were detected. Compositions La0.8 Sr0.2 Cr0.9 Mg0.1O3 and La0.8 Sr0.2 Cr0.85 Mg0.15 O3 here investigated were shown to have negligible thermal expansion mismatch with YSZ electrolytes. The mixed oxide route was also used for comparison.
TL;DR: In this article, an ordered 2D-hexagonal mesoporous Mg and Ta mixed oxide (Mg−Ta oxide) was successfully prepared, which is stable after calcination at 773 K for 30 h.
Abstract: An ordered (2D-hexagonal) mesoporous Mg and Ta mixed oxide (Mg−Ta oxide) is successfully prepared. The mesoporous Mg−Ta oxide is stable after calcination at 773 K for 30 h, and has a BET surface ar...
TL;DR: In this article, a series of catalysts with Mo loading from 2 to 14.5% on MgO-Al 2 O 3 mixed oxide support was prepared by incipient wetness impregnation method.
Abstract: A series of catalyst with Mo loading from 2 to 14 wt.% on MgO–Al 2 O 3 mixed oxide support was prepared by incipient wetness impregnation method. Pure MgO and Al 2 O 3 were prepared by using Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 3 ·9H 2 O salt solutions and urea as hydrolyzing agent. MgO–Al 2 O 3 (1:1) mixed oxide was prepared by co-precipitation of appropriate quantities of magnesium nitrate and aluminum nitrate salts. BET surface area, pore volume, pore size distribution, TPR, acidity and acid strength distributions of catalysts and supports were measured. MgO–Al 2 O 3 (1:1) mixed oxide showed a biomodal pore size distribution. LTOC and TPR results show that an optimum 8% Mo on MgO–Al 2 O 3 is sufficient to form MoO 3 monolayer. TPR technique can also be used as a vital tool to determine the monolayer coverage. HDS activity has been correlated with LTOC. Introduction of basic MgO in the lattice of Al 2 O 3 moderates the strong acidity in MgO–Al 2 O 3 . Impregnation of acidic MoO 3 species further enhances the acidity favorable for HYC.
TL;DR: In this article, it was found that the prepared K2Ta2O6 exhibits the higher activity to photolytic splitting of H2O into H2 than that of KTaO3 which is reported as the active catalyst for the H 2O decomposition.
Abstract: K–Ta mixed oxides with two different crystal structures, i.e. KTaO3 and K2Ta2O6, have been prepared by alkoxide and solid-state reaction routes. K2Ta2O6 single phase with pyrocrhore like structure can be obtained by the alkoxide method, however, this phase cannot be obtained by a conventional solid-state reaction route. It was found that the prepared K2Ta2O6 exhibits the higher activity to photolytic splitting of H2O into H2 than that of KTaO3 which is reported as the active catalyst for the H2O decomposition. Crystalline size of K2Ta2O6 pseudo-pyrochlore oxide can be controlled by the hydrolysis condition for alkoxide. It was seen that the crystalline size has a large influence on the photocatalytic decomposition activity and the highest activity was obtained at the crystal size of 30 nm. Effects of metal loading were also investigated on K2Ta2O6 oxide and among the examined metals, activity to photolysis of water increased by loading Rh. Formation of oxygen was also observed when 0.2 wt.% Rh was loaded.
TL;DR: In this article, the anodic behavior of two titanium cast alloys, obtained by fusion in a voltaic arc under argon atmosphere, was analyzed in aerated aqueous solutions having different pH values.
TL;DR: In this article, the role of tellurium in the catalytic performance of Mo-V-Nb-Te-O mixed oxide catalysts has been discussed, and it has been shown that the performance of these catalysts cannot be explained by the incorporation of Te on the surface of a Mo−V−Nb−O mixed-oxide but by the presence of an orthorhombic Te2M20O57 (M=Mo, V, Nb) crystalline phase.
TL;DR: In this article, a series of x TiO2 (1−x) Al2O3 mixed oxides with different molar ratio, x=0.95, 0.90,0.80, 0,70 and 0.60, have been prepared by a non-alkoxide sol-gel route from a mixture of titania and boehmite sol derived from titanyl sulfate and aluminium nitrate.
TL;DR: The layered precursor of zeolite MCM-22 was pillared with SiO2, Al2O3, MgO−Al 2O3 and BaO−SiO2 to generate new derivatives of MCM36.
Abstract: The layered precursor of zeolite MCM-22 was pillared with SiO2, Al2O3, MgO−Al2O3, BaO−Al2O3, Al2O3−SiO2, MgO−Al2O3−SiO2, and BaO−Al2O3−SiO2 to generate new derivatives of MCM-36. These nanocomposite materials are characterized by a layered structure consisting of microporous zeolite layers and mesoporous slit-shaped galleries formed by the incorporation of pure and mixed oxides between the zeolitic sheets. Enhanced Lewis acidity is generated by pillaring with (mixed) aluminum oxides. The adsorption of 2.6-di-tert-butyl-pyridine (2.6-DTBPy) demonstrated for all materials an increased accessibility to acid sites at the pore mouth or the outer surface of the zeolite layers compared to MCM-22. For (MgO/BaO)−Al2O3−SiO2−MCM-36 additional Bronsted acid sites of higher strength than the sites in the zeolitic sheets are observed, which are assigned to the silica−alumina clusters in the interlayer galleries. Basic properties were introduced by the incorporation of alkaline earth oxide aluminates (MgO/BaO−Al2O3) int...
TL;DR: The general synthesis of metal-silicon mixed-oxide nanocomposite materials, including a variety of both main group and transition metals, in which the metal oxide is the major component is described in this paper.
Abstract: The general synthesis of metal–silicon mixed-oxide nanocomposite materials, including a variety of both main group and transition metals, in which the metal oxide is the major component is described. In a typical synthesis, the metal-oxide precursor, MClx · yH2O(x = 2–6, y = 0–7), was mixed with the silica precursor, tetramethoxysilane (TMOS), in ethanol and gelled using an organic epoxide. The successful preparation of homogeneous, monolithic materials depended on the oxidation state of the metal as well as the epoxide chosen for gelation. The composition of the resulting materials was varied from M/Si = 1–5 (mol/mol) by adjusting the amount of TMOS added to the initial metal-oxide precursor solution. Supercritical processing of the gels in CO2 resulted in monolithic, porous aerogel nanocomposite materials with surface areas ranging from 100–800 m2 g−1. The bulk materials are composed of metal oxide/silica particles that vary in size from 5–20 nm depending on the epoxide used for gelation. Metal oxide and silica dispersion throughout the bulk material is extremely uniform on the nanoscale. The versatility and control of the synthesis method will be discussed as well as the properties of the resulting metal–silicon mixed oxide nanocomposite materials.