Effect of the nature of anions of aluminum salts used to synthesize a precursor of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> ceramics on the stabilization of the tetragonal modification of zirconium dioxide

Samples of a precursor for an aluminum oxide ceramics reinforced with zirconium oxide were synthesized by hydrolysis of various aluminum salts in the presence of a ZrO₂ sol under conditions of urea decomposition at 90°C and pH < 4 maintained, with hydrolysis products deposited onto the surface of ZrO₂ sol particles. It was found that the nature of a salt anion affects the interaction of hydrolysis products of the aluminum cation with the surface of ZrO₂ sol particles. The structure of products formed in thermal treatment of samples of a precursor for Al₂O₃-ZrO₂ (T = 1250°C) was characterized by X-ray phase analysis and scanning electron microscopy. The phase transition temperatures of the oxides Al₂O₃ and ZrO₂ contained in the precursor were estimated using the results of thermal analysis of the samples in the temperature range 20–1300°C.     

Physicochemical study of composite gel in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> system

We show a feasibility of preparing a highly homogeneous composite gel (CG) based on hydrolysis products of Al₂O₃-ZrO₂ salts. The phase composition of a sample calcined at 1250°C for 2 h is as follows: α-Al₂O₃, t-ZrO₂, and m-ZrO₂ where the t-ZrO₂/m-ZrO₂ phase ratio ranges from 2.8 to 3.8 depending on gel preparation conditions. The investigative tools used are powder X-ray diffraction, differential thermal analysis (atmosphere: Ar), and IR spectroscopy.     

Effect of sol-gel derived Al2O3-ZrO2 and Al2O3-TiO2 oxides on the selectivity of NO reduction by CO under oxidizing conditions

The role of Al₂O₃-ZrO₂ and Al₂O₃-TiO₂ sol-gel prepared supports in the activity of platinum for the NO reduction by CO under oxidizing conditions has been studied. ²⁷Al MAS-NMR spectra have shown the formation of pentacoordinate Al^V in alumina-zirconia support. ZrO₂ or TiO₂ crystalline phases cannot be identified by XRD diffraction, suggesting the formation of nanosized structures supported on alumina. When the reaction was carried out in presence of oxygen, large amounts of NO₂ were observed on Pt/Al₂O₃-ZrO₂catalyst, while the formation of N₂O is more prononced on Pt/Al₂O₃-TiO₂ catalyst. The effect of water during NO reduction is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effects of preparation method on the characteristics of alumina-zirconia powders

Two series of Al₂O₃-ZrO₂ powders with various contents of ZrO₂ were synthesized by sol-gel (chemical polymerization) and coprecipitation methods. The effect of ZrO₂ content and preparation method on the structure and texture of the resultant powders were determined. The samples were characterized by nitrogen sorption, thermal gravimetric analysis, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. The sol-gel method yields more homogeneous powder and retards the aggregation of particles. It produces powders with a larger surface area, a smaller pore size, and a narrower pore size distribution than the coprecipitated one. The X-ray diffraction results show that the powders are amorphous at the calcination temperature below 700°C for both methods. Incorporation of zirconia into alumina greatly affects the surface properties of the powders upon heating, exerting a protective effect against sintering, and inhibiting both the crystallization of the -Al₂O₃ phase and the - to -phase transformation. Zirconia is dispersed in alumina matrix and does not form a new structure.     

The electron acceptor and catalytic properties of zirconium dioxide modified with aluminum and gallium oxides

The electron acceptor properties of the mixed oxide systems 20 mol % M₂O₃-ZrO₂ (M = Al, Ga) and 10 mol % M₂O₃-10 mol % Al₂O₃-ZrO₂ (M = Ga, Y) were studied by recording the EPR spectra of paramagnetic complexes of adsorbed anthraquinone. The EPR data were compared with the catalytic activity of the mixed oxides in the decomposition of propanols and butanols in a pulsed microcatalytic reactor. The Al₂O₃-ZrO₂ and Ga₂O₃-ZrO₂ solid solutions were found to be metastable and decompose as the temperature of calcining increased or a third component was introduced. Correspondence between the EPR data and catalytic experiment results was established. This correspondence substantiates the occurrence of the segregation of the Al₂O₃ and Ga₂O₃ amorphous phases on the surface of zirconia, which accompanies the decay of the M₂O₃-ZrO₂ (M = Al, Ga) metastable solid solutions. The Al₂O₃-ZrO₂ solid solution decomposes more readily than Ga₂O₃-ZrO₂.     

Hydrogen Production by Steam Reforming of Ethanol Over Mesoporous Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> Catalysts

This review paper reports the recent progress concerning the application of nickel–alumina–zirconia based catalysts to the ethanol steam reforming for hydrogen production. Several series of mesoporous nickel–alumina–zirconia based catalysts were prepared by an epoxide-initiated sol–gel method. The first series comprised Ni–Al₂O₃–ZrO₂ xerogel catalysts with diverse Zr/Al molar ratios. Chemical species maintained a well-dispersed state, while catalyst acidity decreased with increasing Zr/Al molar ratio. An optimal amount of Zr (Zr/Al molar ratio of 0.2) was required to achieve the highest hydrogen yield. In the second series, Ni–Al₂O₃–ZrO₂ xerogel catalysts with different Ni content were examined. Reducibility and nickel surface area of the catalysts could be modulated by changing nickel content. Ni–Al₂O₃–ZrO₂ catalyst with 15 wt% of nickel content showed the highest nickel surface area and the best catalytic performance. In the catalysts where copper was introduced as an additive (Cu–Ni–Al₂O₃–ZrO₂), it was found that nickel dispersion, nickel surface area, and ethanol adsorption capacity were enhanced at an appropriate amount of copper introduction, leading to a promising catalytic activity. Ni–Sr–Al₂O₃–ZrO₂ catalysts prepared by changing drying method were tested as well. Textural properties of Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst produced from supercritical drying were enhanced when compared to those of xerogel catalyst produced from conventional drying. Nickel dispersion and nickel surface area were higher on Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst, which led to higher hydrogen yield and catalyst stability over Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst.     

Physicochemical properties of precursors of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> oxide ceramics prepared by electrochemical method

Scanning electron microscopy, X-ray, and thermal analysis are used to examine the structure and properties of dispersive systems based on aluminum and zirconium oxides prepared electrochemically. The effect the conditions of synthesis have on the structure and morphology of Al₂O₃–ZrO₂ particles is studied. It is shown that the effect of an electric field on the reaction medium allows us to adjust the physicоchemical properties and morphology.     

Cu/La2O3-ZrO2-Al2O3催化剂的制备及其对NO选择性还原的催化性能

采用将Al(NO3)3、La(NO3)3和ZrOCl2的混合液滴入沉淀剂(NH4)2CO3中的共沉淀法制备La2O3-ZrO2-Al2O3复合载体,然后负载上Cu2+,制成Cu/La2O3-ZrO2-Al2O3催化剂。考察了该催化剂在富氧条件下对C3H6选择还原NO的催化性能,并借助扫描电子显微镜（SEM）、X射线衍射（XRD）、比表面积测定（BET）、吡啶吸附红外光谱（Py-IR）、程序升温还原（TPR）和热重分析（TG）等方法研究催化剂制备方法与结构、性能的关系。实验结果表明,采用将Al(NO3)3滴入(NH4)2CO3制得的γ-Al2O3能有效地增大催化剂的比表面积,加入La2O3能提高催化剂的热稳定性,加入ZrO2能大幅度增加催化剂表面L酸和B酸的酸量。因此,采用共沉淀法制备的La2O3-ZrO2-Al2O3复合载体能够使Cu/La2O3-ZrO2-Al2O3催化剂具有良好的催化性能,最佳催化活性温度为300℃,NO最大转化率高达88.9%,在有10%水蒸气存在的情况下,仍可达81.9%。     

Effect of the composition of the reaction atmosphere on the thermal stability of highly dispersed gold particles on an oxide support (Au/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system)

Metal gold particles were supported onto the surface of aluminum oxide by physical vapor deposition. The effects of thermal treatments at 30?800°C both in a vacuum and in an atmosphere of O₂ (5 mbar), CO (5 mbar), or a mixture of CO + O₂ (5 mbar of each) on the samples of Au/Al₂O₃ were studied by X-ray photoelectron spectroscopy. An increase in the Au4f line intensity in the course of gold deposition was accompanied by a shift of this line toward smaller binding energy. Upon the supporting of a maximum quantity of gold, the binding energy E _b(Au4f _7/2) became smaller than the value characteristic of the bulk metal. It was hypothesized that this can be explained by the formation of negatively charged Au^δ? particles due to electron density transfer from the support to the particles of gold. In the course of the heating of Au/Al₂O₃ in a vacuum or in a reaction atmosphere, the agglomeration of small gold particles occurred; this fact manifested itself in a decrease in the atomic ratio [Au]/[Al]. In all of the atmospheres, the Au particles supported on Al₂O₃ exhibited high thermal stability; considerable changes in the ratio [Au]/[Al] were observed only at temperatures higher than 600°C.     

制备方法对Al2O3掺杂Pt/WO3-ZrO2催化剂上正庚烷异构化反应的影响

采用恒pH法和非恒pH法制备了Al₂O₃掺杂的Pt/WO₃/ZrO₂催化剂,并用N₂吸附-脱附、X射线衍射、紫外-可见漫反射、CO化学吸附、X射线光电子能谱、²⁷Al魔角旋转核磁共振和吡啶吸附红外等技术对催化剂进行了表征.结果表明,相比于非恒pH法制备的催化剂,恒pH法制备的催化剂具有较高的比表面积和Pt分散度,在H₂气氛中产生更多的B酸位,从而表现出更高的催化正庚烷临氢异构化反应活性; 在200℃和质量空速0.9h^-1的反应条件下,正庚烷转化率达70.0%,明显高于非恒pH法制备的催化剂(43.5%).     

Formation and transformation of Al<Subscript>13</Subscript> from freshly formed precipitate in partially neutralized Al(III) solution

Al₁₃ is one of the novel nanospecies in partially neutralized Al(III) solution and Al-OH sol or precipitate could be generated simultaneously in the neutralization. Unfortunately, the precipitate is believed to be harmful to the formation of Al₁₃ due to the consumption of Al(OH)₄ ⁻, which was regarded as the precursor of Al₁₃. In this paper, the feasibility and potential of transformation of freshly formed Al-OH precipitate into Al₁₃ species were studied by using ferron colorimetric method and ²⁷Al NMR spectroscopy. The Al-OH precipitates were produced by two ways: injection of base solution into Al(III) solution gradually and mixing of Al(III) and base solutions instantaneously. The re-dissolving behaviors of the freshly formed precipitates were examined under different basicities (OH/Al molar ratio) and temperatures. It has been shown that Al₁₃ could be formed through the re-dissolution of intermediate Al-OH precipitate generated in partially neutralized Al(III) solution. A possible formation mechanism of Al₁₃ was suggested. Easily transformable precipitate was developed when the OH/Al molar ratio was less than 2.5. Rapid re-dissolution of freshly formed precipitate was favorable for Al₁₃ formation, which could be enhanced by heating.     

Al含量对Pt-SO2-4 /ZrO2-Al2O3固体超强酸催化

通过向SO^2-₄ /ZrO₂催化剂中同时引入适量的Pt和Al₂O₃, 制备出了具有较高催化性能和稳定性的Pt-SO^2-₄ /ZrO₂-Al₂O₃型固体超强酸催化剂. 以正戊烷异构化反应为探针, 考察了Al含量对催化剂性能的影响; 并采用X射线衍射(XRD)、比表面积测定(BET)、红外(IR)光谱、程序升温还原(TPR)、热重-差热分析(TG-DTA)和氨-程序升温脱附(NH₃-TPD)手段对催化剂进行了表征. 结果表明, Al能够提高ZrO₂的晶化温度, 抑制硫的分解, 增加催化剂的比表面积, 增强硫氧键的结合, 提高催化剂的还原性能, 增加催化剂的酸强度和酸总量. 当Al₂O₃含量(质量分数, w)为5.0%时, Pt-SO^2-₄ /ZrO₂-Al₂O₃固体超强酸催化剂的催化活性最好, 在100 h内异戊烷收率可稳定在52.0%以上, 选择性在98.2%以上.     

负载型钌催化剂催化山梨醇氢解制乙二醇(英)

Supported Ru catalysts were prepared by wet impregnation to evaluate the role of different oxide supports（Al₂O₃,SiO₂,TiO₂,ZrO₂） in sorbitol hydrogenolysis to glycols.X-ray diffraction,transmission electron microscopy,hydrogen chemisorption,X-ray photoelectron spectroscopy,and NH3temperature-programmed desorption were used to characterize the catalysts,which were active in the hydrogenolysis of sorbitol.The support affected both the physicochemical properties and catalytic behavior of the supported Ru particles.The characterization results revealed that the Ru/Al₂O₃catalyst has a high surface acidity,partially oxidized Ru species on the surface,and a higher surface Ru/Al atomic ratio,which gave it the highest selectivity and yield to glycols.     

New method for development of carbon clad silica phases for liquid chromatography: Part I. Preparation of carbon phases

Owing to its combination of unique selectivity and mechanical strength, commercial carbon clad zirconia (C/ZrO₂) has been widely used for many applications, including fast two-dimensional liquid chromatography (2DLC). However, the low surface area available (only 20–30 m²/g for commercial porous ZrO₂) limits its retentivity. We have recently addressed this limitation by developing a carbon phase coated on the high surface area of HPLC grade alumina (C/Al₂O₃). This material provides higher retentivity and comparable selectivity, but its use is still limited by how few HPLC quality types of alumina particles (e.g., particle size, surface area, and pore size) are available. In this work, we have developed useful carbon phases on silica particles, which are available in various particle sizes, pore sizes and forms of HPLC grade. To make the carbon phase on silica, we first treat the silica surface with a monolayer or less of metal cations that bind to deprotonated silanols to provide catalytic sites for carbon deposition. After Al (III) treatment, a carbon phase is formed on the silica surface by chemical vapor deposition at 700 °C using hexane as the carbon source. The amount of Al (III) on the surface was varied to assess its effect on carbon deposition, and the carbon loading was varied at different Al (III) levels to assess its effect on the chromatographic properties of the various carbon adsorbents. We observed that use of a concentration of Al (III) corresponding to a full monolayer leads to the most uniform carbon coating. A carbon coating sufficient to cover all the Al (III) sites, required about 4–5 monolayers in this work, provided the best chromatographic performance. The resulting carbon phases behave as reversed phases with reasonable efficiency (50,000–79,000 plates/m) for non-aromatic test species.     

Hydrated surface structure and its impacts on the stabilization of t-ZrO2

We first optimized the preparation conditions to 3.6-6.0 nm ZrO₂ in a pure tetragonal structure (t-phase). All samples were characterized by X-ray diffraction, high-resolution transmission electron microscope, thermal analysis, Raman spectra, and infrared spectra. It is found that the surfaces of t-ZrO₂ nanostructures were terminated by an amorphous hydration layer co-existing with small amounts of carbonate molecules. With the removal of hydrated surface layers under hydrothermal conditions at T>150 °C, t-ZrO₂ nanostructures became thermodynamically unstable, which partially transformed into monoclinic ZrO₂ (m-phase). Such a transformation occurs initially at surface regions and then develops into the bulk. High-temperature annealing in air could also remove the hydrated surface layers, which is however followed by a gradual transformation of t-ZrO₂ into m-ZrO₂ in both bulk and surface regions. These observations are explained in terms of the difference in surface free energies of m-ZrO₂ and t-ZrO₂ upon H₂O adsorption.     

Cr(III) in gahnite-containing transparent glass-ceramics: Influence of melting conditions and heat treatment on crystallization and spectroscopic properties

Transparent glass ceramics with Cr(III) were obtained by different thermal treatment of glass with composition (mol%) 73.6 SiO₂,11.8 Al₂O₃, 4.2 Li₂O, 7.0 ZnO, 1.6 TiO₂, 1.5 ZrO₂, 0.3 As₂O₃, 0.024 Cr₂O₃, melted under various conditions. Parallel measurements of X-ray diffraction, optical and EPR spectra reveal the different formation ofgahnite from precursor glass or petalite-like phase.     

The influence of the method of addition of Al2O3 to 3YSZ material on its thermal and electrical properties

The properties of tetragonal yttria-stabilized zirconia composites with the small addition of alumina (Al₂O₃?Y₂O₃?ZrO₂ composite) obtained on two ways of synthesis were studied in terms of usability for anode materials in solid oxide fuel cell. Both methods were based on citric synthesis: in the first one, Al₂O₃ was coprecipitated with the tetragonal ZrO₂ in the form of citrate by citric acid, while in the second Al₂O₃ was impregnated in the form of aluminium nitrate precursor on tetragonal ZrO₂ matrix. The obtained materials were analysed by X-ray diffraction, dilatometry and impedance spectroscopy. The results of measurements show that regardless of synthesis method, the addition of Al₂O₃ influences the conductivity of samples by increasing their grain boundaries conductivity as an effect of removing of SiO₂ and decreasing of conductivity activation energy. The impregnation of Al₂O₃ on tetragonal ZrO₂ and sintering of this material above shrinking temperature cause, however, radical decrease of porosity of materials, which disqualifies these samples as anode materials. In the case of samples obtained by coprecipitation the significant decrease of porosity is not observed.     

The Synthesis of Stable, High Solid Content Alumina Sol

The stable alumina sol with an ASB/water molar ratio of 1:30 could not be obtained via the general peptization process because gelation occurred immediately. With the addition of EAcAc the stability of this sol was greatly improved. The studies using TEM, UV-V is and IR spectra revealed that a surface modification layer was formed around the Al₂O₃ colloidal particle through the chelating reaction of EAcAc with the surface HO-Al groups. The Al₂O₃ colloidal particles were therefore sufficiently capped and the growth of the colloidal particles was effectively prevented.     

Sol-Emulsion-Gel Synthesis of Alumina-Zirconia Composite Microspheres

Oxide microspheres in the system Al₂O₃-ZrO₂ (AZ), with the Al₂O₃:ZrO₂ molar ratios as 87:13, 78:22, 74:26 and 64:36 were obtained from emulsified bi-component sols by the sol-emulsion-gel method. The surfactant concentration and viscosity of the sols were found to affect the characteristics of the derived microspheres. The gel and calcined microspheres were investigated by using thermogravimetry analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD), optical and scanning electron microscopy (SEM) and particle size analysis. TGA indicated the removal of most of the volatiles, i.e. 40 ± 2 wt% up to about 500°C. Crystallization of gel microspheres at about 900°C was confirmed by DTA and XRD. XRD results also indicated the retainment of tetragonal (t-)ZrO₂, in the absence of stabilizers, at 1600°C. The optical and scanning electron microscopy confirmed the spherical morphology of the gel and calcined particles. The particle size distribution of the AZ microspheres calcined at 1200°C for 1 h exhibited a size range of 5–60 m with the average particle size (d ₅₀) varied from 23 to 26 m.     

The properties of nickel aluminate nanoparticles prepared by sol–gel and impregnation methods

Nickel aluminates were prepared by sol–gel and impregnation methods and calcined at 1100 °C. The sol–gel made samples were prepared with different amounts of nickel (Ni/Al molar ratio equal to 0, 0.25, 0.5, and 0.75) and aging times (24 and 48 h). The samples were characterized by X-ray diffraction, induced couple plasma, nitrogen physisorption, transmission and scanning electron microscopy, and ammonia temperature programmed desorption (NH₃-TPD). In the sol–gel made samples, only the NiAl₂O₄ structure of nickel aluminate was defined, while for impregnation, NiAl₁₀O₁₆ was formed as well. The sol–gel made samples had low specific surface areas (7.7–12.4 m²/g), but a sample prepared by impregnation method had higher specific surface area (67.2 m²/g). The surface acidity density decreased by increasing the amount of nickel and was the lowest for impregnation method.