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1.
SiO 2/ZrO 2/C carbon ceramic material with composition (in wt%) SiO 2 = 50, ZrO 2 = 20, and C = 30 was prepared by the sol–gel-processing method. A high-resolution transmission electron microscopy image
showed that ZrO 2 and the graphite particles are well dispersed inside the matrix. The electrical conductivity obtained for the pressed disks
of the material was 18 S cm −1, indicating that C particles are also well interconnected inside the solid. An electrode modified with flavin adenine dinucleotide
(FAD) prepared by immersing the solid SiO 2/ZrO 2/C, molded as a pressed disk, inside a FAD solution (1.0 × 10 −3 mol L −1) was used to investigate the electrocatalytic reduction of bromate and iodate. The reduction of both ions occurred at a peak
potential of −0.41 V vs. the saturated calomel reference electrode. The linear response range (lrr) and detection limit (dl)
were: BrO 3
−, lrr = 4.98 × 10 −5–1.23 × 10 −3 mol L −1 and dl = 2.33 μmol L −1; IO 3
−, lrr = 4.98 × 10 −5 up to 2.42 × 10 −3 and dl = 1.46 μmol L −1 for iodate. 相似文献
2.
The Ni/SiO 2, Ni/ZrO 2, and Ni/SO 4/ZrO 2 systems were studied by diffuse-reflectance IR spectroscopy using CO as a probe molecule. The Ni/SiO 2 and Ni/ZrO 2 systems are similar in properties, and the state of nickel in the Ni/ZrO 2 system is determined by the specific surface area. In the Ni/SO 4/ZrO 2 system, the surface sulfur compounds affect substantially the state of nickel: Ni δ+ species with a partial positive charge are formed due to the strong electron-acceptor properties of the sulfur compounds.
Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 409–413, March, 1998. 相似文献
3.
A series of MoO 3/γ-Al 2O 3 catalysts with different Mo surface densities (Mo atoms/nm 2) has been prepared by incipient wetness impregnation method. Structural characteristics of the prepared catalysts were investigated
by atomic absorption spectroscopy, X-ray diffraction, Fourier Transform Infrared spectroscopy, N 2 adsorption at −196 °C, and temperature-programmed reduction (TPR). The catalytic activities of the prepared catalysts were
tested by cyclohexene conversion between 200 and 400 °C. XRD results indicated that molybdenum oxide species were dispersed
as a monolayer on the support up to 4.04 Mo atoms/nm 2, and the formation of crystalline MoO 3 was observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in
tetrahedral form at lower loading, and polymeric octahedral forms were dominant at higher loading. Cyclohexene conversion
reaction proceeded mainly through the simple dehydrogenation pathway in the studied temperature range 200–400 °C and was found
to be highly dependent on MoO 3 dispersion. 相似文献
4.
Sulfur‐resistant methanation of syngas was studied over MoO 3–ZrO 2 catalysts at 400°C. The MoO 3–ZrO 2 solid‐solution catalysts were prepared using the solution combustion method by varying MoO 3 content and temperature. The 15MoO 3–ZrO 2 catalyst achieved the highest methanation performance with CO conversion up to 80% at 400°C. The structure of ZrO 2 and dispersed MoO 3 species was characterized using X‐ray diffraction and transmission electron microscopy. The energy‐dispersive spectrum of the 15MoO 3–ZrO 2 catalyst showed that the solution combustion method gave well‐dispersed MoO 3 particles on the surface of ZrO 2. The structure of the catalysts depends on the Mo surface density. It was observed that in the 15MoO 3–ZrO 2 catalyst the Mo surface density of 4.2 Mo atoms nm ?2 approaches the theoretical monolayer capacity of 5 Mo atoms nm ?2. The addition of a small amount of MoO 3 to ZrO 2 led to higher tetragonal content of ZrO 2 along with a reduction of particle size. This leads to an efficient catalyst for the low‐temperature CO methanation process. 相似文献
5.
The physicochemical properties of the surface of the Y 0.1Ce
x
Zr 1−x
O 2−δ, La 0.1Ce
x
Zr 1−x
O 2−δ ( x=0.1–0.7), and Y 0.1Pr 0.3Zr 0.6O 2−δ. complex oxide systems were studied using IR and X-ray photoelectron spectroscopies. An appreciable enrichment of the surface
of the solids in rare-earth-metal cations (cerium or praseodymium) during the synthesis was revealed. While cations are uniformly
spread over the surface of cerium-zirconium solid solutions, the Y 0.1Pr 0.3Zr 0.6O 2−δ surface is covered by the clusters or even a phase of praseodymia. Reductive treatment in hydrogen with subsequent reoxidation
results in the segregation of cerium ions on the Y 0.1Ce 0.3Zr 0.6O 2−δ surface at a temperature as low as 770 K.
Original Russian Text ? A.N. Kharlanov, L.N. Ikryannikova, V.V. Lunin, A. Yu. Stakheev, 2007, published in Zhurnal Fizicheskoi
Khimii, 2007, Vol. 81, No. 7, pp. 1271–1277. 相似文献
6.
The effects of various factors on the formation of O 2
– radical anions in the adsorption of an NO + O 2 or NO 2 + O 2 mixture on ZrO 2 were studied. It was found that the thermal stability of the O 2
– species depends on the composition of the adsorbed gas. It was suggested that nitrogen oxide complexes on ZrO 2 centers are responsible for the formation of O 2
–. These centers are formed upon the treatment of the oxide in a vacuum; however, they are different from both coordinatively unsaturated Zr 4+ cations (NO adsorption centers at 77 K) and Zr 4+–O ––O ––Zr 4+ centers, at which O 2
– are formed because of the adsorption of H 2 + O 2. Based on the experimental data, the mechanism of O 2
– formation in the adsorption of an NO + O 2 mixture is discussed. 相似文献
7.
The influence of the alumina support on the catalytic activity of Pt/Al 2O 3 catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation
of γ-, δ-, and α-alumina with H 2PtCl 6. The highest rate of hydrogen production (452 μmol min −1 g −1) obtained with the Pt/α-Al 2O 3 catalyst can be related to the highest extent of dispersion of Pt on α-Al 2O 3. XPS, TEM-EDX and TPR-H 2 measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al 2O 3 catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al 2O 3 and Pr/δ-Al 2O 3 catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this
way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different
coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between
Pt and the support. 相似文献
8.
It was established by X-ray diffraction, TPR, and EPR that microemulsion (m.e.) synthesis yields the binary oxides ZrO 2(m.e.) and CeO 2(m.e.) and the mixed oxide Zr 0.5Ce 0.5O 2(m.e.) in the form of a tetragonal, cubic, and pseudocubic phase, respectively, having crystallite sizes of 5–6 nm. The bond
energy of surface oxygen in the (m.e.) samples is lower than in their analogues prepared by pyrolysis. Hydrogen oxidation
on the oxides under study occurs at higher temperatures than CO oxidation. ZrO 2(m.e.) and CeO 2(m.e.) are active in O 2− formation during NO + O 2 adsorption, while CeO 2 is active during CO + O 2 adsorption, too. However, its amount here is one-half to one-third its amount in the pyrolysis-prepared samples, signifying
a reduced number of active sites, which are Zr 4+ and Ce 4+ coordinatively unsaturated cations and Me 4+-O 2− pairs. O 2− radical anions are stabilized in the coordination sphere of Zr 4+ coordinatively unsaturated cations via ionic bonding, and in the sphere of Ce 4+ cations, via covalent bonding. Ionic bonds are stronger than ionic-covalent bonds and do not depend on the ZrO 2 phase composition. Zr 0.5Ce 0.5O 2 is inactive in these reactions because of the strong interaction of Zr and Ce cations. It is suggested that Ce (4 + β)+ coordinatively unsaturated cations exist on its surface, and their acid strength is lower than that of Zr 4+ and Ce 4+ cations in ZrO 2 and CeO 2, according to the order ZrO 2 > CeO 2 ≥ Zr 0.5Ce 0.5O 2. Neither TPR nor adsorption of probe molecules revealed Zr cations on the surface of the mixed oxide. 相似文献
9.
In order to obtain a catalyst support with a high surface area, ZrO 2 and ZrO 2-Y 2O 3 were prepared by the hydrolytic decomposition of the corresponding isopropoxide dissolved in benzene. The hydrolysis was carried out at 80°C using an excess amount of distilled water in flowing dry nitrogen. The precipitates thus obtained were dried at 100°C followed by calcination at 500°C in air or nitrogen for 1 h. The specific surface areas for both of the ZrO 2 and ZrO 2-Y 2O 3 increased with increasing amount of water added for hydrolysis, and the surface areas for ZrO 2-Y 2O 3 increased with increasing yttrium content. A ZrO 2 having a surface area of 130 m 2/g was produced, and a stabilized tetragonal ZrO 2 with 15 mol% Y 3+ having a surface area of 200 m 2/g was produced. Furthermore, despite the difference in the ZrO 2 and ZrO 2-Y 2O 3 crystal structures, the lattice-strain of ZrO 2 has been unequivocally related to the surface area. 相似文献
10.
The alkoxido-titanium pentamolybdate [( iPrO)TiMo 5O 18] 3− ( 1) has been obtained as its tetrabutylammonium (TBA) salt by hydrolysis of a mixture containing (TBA) 2[Mo 2O 7], (TBA) 4[Mo 8O 26] and Ti(O iPr) 4 in MeCN and has been characterised by 1H, 13C, 17O, 49Ti and 95Mo NMR and FTIR spectroscopy, electrospray ionisation mass spectrometry, elemental microanalysis and single-crystal X-ray
crystallography. The Lindqvist-type structure is derived from [Mo 6O 19] 2− by replacement of {Mo=O} 4+ by {( iPrO)Ti} 3+ and shows bond alternation in the TiMo 3O 4 rings, with average bond distances of 1.956(8) ? for Ti–O(Mo), 1.832(7) ? for Mo–O(Ti), 1.943(7) ? for Mo eq–O(Mo ax) and 1.910(6) ? for Mo ax–O(Mo eq), while the increase in charge results in a decrease in 17O NMR chemical shift for terminal Mo=O groups from δ 933 for [Mo 6O 19] 2− to δ 875 and 857 for 1 and a shift in ν Mo=O from 951 cm −1 for [Mo 6O 19] 2− to 930 cm −1 for 1. The main peaks in the negative-ion electrospray ionisation mass spectrum of (TBA) 3
1 could be assigned to ion aggregates containing 1 or fragments derived from 1, including {(TBA) 2[( iPrO)TiMo 5O 18]} −, {(TBA)[( iPrO)TiMo 5O 18]} 2−, {( iPrO)TiMo 2O 8} −, {TiMo 5O 18} 2−, {TiMo 4O 15} 2− and {Mo 3O 10} 2−. 相似文献
11.
A kinetic model of radiation-chemical transformations of nitrogen oxide and nitrites in aqueous solutions is proposed. It
includes the previously developed reaction scheme for water and H 2, H 2O 2, and O 2 solutions complemented by the reactions of water radiolysis products with NO and NO 2−. It has been shown that the model describes well experimental data on the decomposition of the compounds and the buildup
of products depending on the absorbed dose in aqueous solutions at different pH values. 相似文献
12.
Reactive species generated in the gas and in water by cold air plasma of the transient spark discharge in various N2/O2 gas mixtures (including pure N2 and pure O2) have been examined. The discharge was operated without/with circulated water driven down the inclined grounded electrode. Without water, NO and NO2 are typically produced with maximum concentrations at 50% O2. N2O was also present for low O2 contents (up to 20%), while O3 was generated only in pure O2. With water, gaseous NO and NO2 concentrations were lower, N2O was completely suppressed and HNO2 increased; and O3 was lowered in O2 gas. All species production decreased with the gas flow rate increasing from 0.5 to 2.2 L/min. Liquid phase species (H2O2, NO2 ̄, NO3 ̄, ·OH) were detected in plasma treated water. H2O2 reached the highest concentrations in pure N2 and O2. On the other hand, nitrites NO2 ̄ and nitrates NO3 ̄ peaked between 20 and 80% O2 and were associated with pH reduction. The concentrations of all species increased with the plasma treatment time. Aqueous ·OH radicals were analyzed by terephthalic acid fluorescence and their concentration correlated with H2O2. The antibacterial efficacy of the transient spark on bacteria in water increased with water treatment time and was found the strongest in the air-like mixture thanks to the peroxynitrite formation. Yet, significant antibacterial effects were found even in pure N2 and in pure O2 most likely due to high ·OH radical concentrations. Controlling the N2/O2 ratio in the gas mixture, gas flow rate, and water treatment time enables tuning the antibacterial efficacy. 相似文献
13.
We have used IR spectroscopy to study adsorption of NO, propene, and their mixture on Rh-Cr 2O 3/ZrO 2 and Rh-CeO 2/ZrO 2 catalysts at temperatures of 293-623 K. We have established that adsorption and coadsorption of the reagents (NO and C 3H 6) have important differences, depending on the nature of the surface. Weak adsorption interactions of the reaction mixture on Rh-CeO 2/ZrO 2 lead to significantly lower activity of this catalyst in selective catalytic reduction (SCR) of NO by propene. 相似文献
14.
The thallium-barium double nitrite, TlBa 2(NO 2)5, is pyroelectric in the 77-600 K range and crystallizes in the Pca2
1 space group. The lattice constants at 293 K are: a = 17.868(12), b = 4.934(3), c = 13-426(11) A (MoKa, λ = 0.71069 A). There are four stoichiometric units in the unit cell of volume V= 1184(1) A 3 ( D
o = 3.98, D
x = 3.979 Mgm −3), F (000) = 1232, μ = 20.36mm −1. The crystal structure was solved by Patterson and Fourier methods and refined by least-squares to a final conventional agreement
index R = 0.053 for 1371 independent reflections collected in a θ range of 3–30°, using MoKα radiation. There are two independent
barium atoms surrounded by NO
2
−
groups, both with coordination number 10 and distances in the ranges Ba-O = 2.69(4)-3.18(4) A and Ba-N = 3.01(4)-3.18(4)
A. The environment of thallium is clearly affected by the lone-pair stereoactivity and involves 12 Tl-O and Tl-N contacts
less than 3.5A, but only four Tl-O distances are shorter than 3 A (min. 2.76(2), max. 2.85(3) A), with a pyramidal coordination
and thallium at the apex of the pyramid. All these coordination polyhedra are joined in chains running along the shortest
lattice vector [010].
The single crystal electronic spectra, studied in absorption with polarized light and in photostimulated emission, are interpreted
as due to transitions involving NO
2
−
electronic levels perturbed by Tl +, whose spin-orbit interaction makes probable also the forbidden singlet-triplet transitions, in agreement with the interpretative
picture given for post-transition metal nitrites. 相似文献
15.
Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active
site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal
model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures,
the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder
Pd/Al 2O 3 catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the
step sites act as the catalytic active site for NO decomposition on Pd/Al 2O 3. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science
study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co 3O 4 serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed
in which the reaction is initiated by NO adsorption onto alkali metals to form NO 2− species and then NO 2− species react with the adsorbed NO species to form N 2 over the interface between the alkali metal and Co 3O 4. 相似文献
16.
Strategies for countering the solubility of LiMn 2O 4 (spinel) electrodes at 50 °C and for suppressing the reactivity of layered LiMO 2 (M=Co, Ni, Mn, Li) electrodes at high potentials are discussed. Surface treatment of LiMn 2O 4 with colloidal zirconia (ZrO 2) dramatically improves the cycling stability of the spinel electrode at 50 °C in Li/LiMn 2O 4 cells. ZrO 2-coated LiMn 0.5Ni 0.5O 2 electrodes provide a superior capacity and cycling stability to uncoated electrodes when charged to a high potential (4.6 V vs Li 0). The use of Li 2ZrO 3, which is structurally more compatible with spinel and layered electrodes than ZrO 2 and which can act as a Li +-ion conductor, has been evaluated in composite 0.03Li 2ZrO 3 · 0.97LiMn 0.5Ni 0.5O 2 electrodes; glassy Li xZrO 2 + x/2 (0< x⩽2) products can be produced from colloidal ZrO 2 for surface coatings. 相似文献
17.
Manganese-yttrium-zirconium mixed oxide nanocomposites with three different Mn loadings (5, 15 and 30 wt%) were prepared by
sol–gel synthesis. Amorphous xerogels were obtained for each composition. Their structural evolution with the temperature
and textural properties were examined by thermogravimetry/differential thermal analysis, X-ray diffraction, diffuse reflectance
UV–vis spectroscopy and N 2 adsorption isotherms. Mesoporous materials with high surface area values (70–100 m 2 g −1) were obtained by annealing in air at 550 °C. They are amorphous or contain nanocrystals of the tetragonal ZrO 2 phase (T-ZrO 2) depending on the Mn amount and exhibit Mn species with oxidation state higher than 2 as confirmed by temperature programmed
reduction experiments. T-ZrO 2 is the only crystallizing phase at 700 °C while the monoclinic polymorph and Mn 3O 4 start to appear only after a prolonged annealing at 1,000 °C. The samples annealed at 550 °C were studied as catalysts for
H 2O 2 decomposition in liquid phase. Their catalytic activity was higher than that of previously studied Mn/Zr oxide systems prepared
by impregnation. Catalytic data were described by a rate equation of Langmuir type. The decrease of catalytic activity with
time was related to dissolution of a limited fraction (up to 15%) of Mn into the H 2O 2/H 2O solution. 相似文献
18.
A detailed investigation of sulphided Co/Mo/Al 2O 3 catalysts, their oxide precursors and several model oxides and sulphides of cobalt and molybdenum has been carried out using
x-ray photoelectron spectroscopy and x-ray absorption spectroscopy ( xanes and exafs). Octahedrally coordinated Co(II) and Mo(IV) are shown to be present in a sulphidic environment on the surfaces of these
catalysts. The surface species contain an excess of sulphur, probably involving disulphide linkages. The surface compositions
of the catalysts examined conform to the general formula Co 11 Mo
2n
IV
(2n + 3) S
2
2−
(2n -2)S 2−. 相似文献
19.
Metal promoted zirconia-based oxide sorbents, such as Pt–ZrO 2/Al 2O 3 for NO x have been investigated. To clarify the role of the catalyst component, sorption of NO and NO 2 was compared using the samples with and without Pt. The catalytic oxidation of NO to NO 2 and successively to nitrate ions is an important role for the Pt catalyst. The experimental results indicate that a high-temperature calcination is essential to remove residual Cl from Pt–ZrO 2–Al 2O 3 prepared from H 2PtCl 6 in order to provide more active NO x sorption sites. Of M–ZrO 2–Al 2O 3 samples investigated, ruthenium as well as Pt demonstrated relatively good performance as a catalyst component in the sorbent. The FT-IR spectra after sorption of NO and NO 2 demonstrated a strong band attributed to stored nitrate ions. The Pt catalyst was more resistant to sulfur poisoning than a base metal catalyst. However, the NO x sorptive capacities of the Pt–ZrO 2/Al 2O 3 sorbents were expected to be deteriorated in dilute SO 2 as far as observed from FT-IR spectra. 相似文献
20.
The first part of this paper deals with the morphology of the MoS 2 phase and its oxide precursor, the MoO 3 phase, mainly from a geometrical point of view. After giving a brief review of the literature describing the structure of
these compounds, Mo densities in both phases were calculated along various crystallographic planes. Further, using structural
models recently proposed by others, Mo densities in MoS 2 were also calculated in the case of an epitactic growth on γ-Al 2O 3 and TiO 2 model surfaces. Then, the calculated Mo densities were compared with experimental results (Mo density when HDS activity is
maximal) previously obtained for catalysts constituted of MoS 2 supported on a low SSA TiO 2, a high SSA TiO 2 and a conventional γ-alumina. It was suggested that either on alumina or titania the MoS 2 phase is growing as (100) MoS 2 planes. However, while on the alumina the optimal MoS 2 phase might be constituted of dispersed MoS 2 slabs covering only a part of the alumina surface (2.9–3.9 Mo atoms/nm 2), on titania the optimal MoS 2 phase might be constituted of a uniform MoS 2 monolayer (5.2 atoms/nm 2 for the high SSA titania, which is equal to the Mo density of a perfect MoS 2 (100) plane). This difference may originate in the creation of a 'TiMoS' phase enhancing the S atoms mobility over Mo/TiO 2-sulfided catalysts. Indeed, while in the case of a γ-alumina carrier the active sites (labile S atoms) are located on the edge of MoS 2 slabs making the ratio Mo edge/Mo total a crucial parameter for the catalytic performances, in the case of a titania carrier the labile sulfur atoms might be statistically
distributed all over the TiMoS active phase. Further, the higher Mo density observed over the high SSA titania (5.2 atoms/nm 2) when compared to that over the low SSA titania (4.2 atoms/nm 2) was supposedly due to the pH-swing method advantageously used to prepare the former carrier. Indeed, this method allows
giving a solid with enhanced mechanical properties providing a good stability to the derived catalysts under experimental
conditions. In addition, this TiO 2 carrier exhibits a great homogeneity, with a surface structure substantially uniform, which might be adequate for a long-range
growth of (100) MoS 2 slabs. 相似文献
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