Investigation of the Cu-Zr-Y oxides activity in the carbon black catalytic oxidation by differential thermal analysis and temperature programmed reduction

Different copper/zirconium-yttrium catalysts have been tested in carbon black oxidation reaction. Supported mainly on differential thermal analysis and temperature programmed reduction, two different mechanisms have been proposed to explain the catalytic results. In the absence of copper, it has been shown that Zr³⁺ ions and associated anionic vacancies are responsible to the catalytic enhancement observed in the mixed oxides, oxygen species being activated on these sites. Among mixed zirconia-yttria solids, ZrO₂-5 mol%Y₂O₃ is the most active catalyst. Copper impregnation on these oxides leads to the formation of different copper species. Small particles of CuO in low interaction with the support, induce a catalytic improvement due to the highest reducibility of these species. Moreover, in order to be more efficient, CuO species should have some interactions with the support, since impregnated samples are more active than the simple mechanical mixtures.     

The ESR Study of O2 – Radical Anion Formation during Adsorption of an NO + O2 Mixture and O2 on ZrO2 and (0.1–2.0)% MoO3/ZrO2

The influence of conditions of the preliminary thermal treatment of ZrO₂, ammonia and methanol adsorption, and MoO₃ supporting on O₂ ^– formation during the adsorption of an NO + O₂ mixture was studied. The interaction of O₂ ^– with different molecules was studied. Adsorbed ammonia and methanol, as well as supported Mo⁶⁺ ions, were shown to inhibit this reaction. The involvement of the Zr⁴⁺ and O^2– Lewis sites in the reaction was concluded. The interaction of ammonia and methanol with the O₂ ^– radical anions changed the g tensor parameters and decreased the thermal stability of O₂ ^– in the case of methanol. O₂ ^– radical anions were formed on the reduced (0.1–2.0)% MoO₃/ZrO₂ samples during the interaction of O₂ with the Mo⁵⁺ ions in the octahedral configuration. As in the case of O₂ ^– formation during NO + O₂ adsorption on ZrO₂, the radical anions were localized in the coordination spheres of the coordinately unsaturated Zr⁴⁺ ions. A change in the MoO₃ content of the samples from 0.1 to 0.5% led to an increase in the amount of O₂ ^–, whereas a change from 0.5 to 2.0% led to a decrease in the O₂ ^– amount due to the screening of the Zr⁴⁺ ions by oxo complexes and polymolybdates.     

ESR Study of the Formation of O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> Radical Anions on Oxidized CeO<Subscript>2</Subscript> and CeO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> Adsorbing a CO + O<Subscript>2</Subscript> Mixture

It is demonstrated by ESR measurements that O ₂ ⁻ (CO + O₂) radical anions result from CO + O₂ adsorption on the oxidized surface of CeO₂. These radical anions are stabilized in the coordination sphere of Ce⁴⁺ cations located in isolated and associated anionic vacancies. This reaction shows an activation behavior determined by CO adsorption. The variation of O ₂ ⁻ (CO + O₂) concentration with CO adsorption temperature suggests that surface carbonates and carboxylates participate in this reaction. In the (0.5– 10.0)%CeO₂/ZrO₂ system, O ₂ ⁻ forms on supported CeO₂ and is stabilized on Ce⁴⁺ and Zr⁴⁺ cations. The stability of O ₂ ⁻ -Ce⁴⁺ complexes is lower on supported CeO₂ than on unsupported CeO₂, indicating a strong interaction between the cerium cations and the support.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 423–429.Original Russian Text Copyright © 2005 by Il’ichev, Kuli-zade, Korchak.     

Role of yttrium loading in the physico-chemical properties and soot combustion activity of ceria and ceria–zirconia catalysts

Ce_1−xY_xO₂ and Ce_0.85−xZr_0.15Y_xO₂ mixed oxides have been prepared by 1000 °C-nitrates calcination to ensure thermally stable catalysts. The physico-chemical properties of the mixed oxides have been studied by N₂ adsorption at −196 °C, XPS, XRD, Raman spectroscopy and H₂-TPR, and the catalytic activity for soot oxidation in air has been studied by TG in the loose and tight contact modes. Yttrium is accumulated at the surface of Ce_1−xY_xO₂ and Ce_0.85−xZr_0.15Y_xO₂, and this accumulation is more pronounced for the former formulation than for the latter, because the deformation of the lattice due to zirconium doping favours yttrium incorporation. Yttrium and zirconium exhibit opposite effects on the surface concentration of cerium; while zirconium promotes the formation of cerium-rich surfaces, yttrium hinders the accumulation of cerium on the surface. For experiments in tight contact between soot and catalyst, all the Ce_1−xY_xO₂ catalysts are more active than bare CeO₂, and Ce_0.99Y_0.01O₂ is the most active catalyst. The benefit of yttrium doping in catalytic activity of ceria can be related to two facts: (i) the Y³⁺ surface enrichment hinders crystallite growth; (ii) the surface segregation of Y³⁺ promotes oxygen vacancies creation. High yttrium loading (x = 0.12) is less effective than low dosage (x = 0.01) because yttrium is mainly accumulated at the surface of the particles and hinders the participation of cerium in the soot oxidation reaction, which is the active component. For the mixed oxides with formulation Ce_0.85−xZr_0.15Y_xO₂ (operating in tight contact) the effect of zirconium on the catalytic activity prevails with respect to that of yttrium. For experiments in loose contact between soot and catalyst, the catalytic activity depends on their BET surface area, and the catalysts Ce_0.85−xZr_0.15Y_xO₂ (BET = 10–13 m²/g) are more active than the catalysts Ce_1−xY_xO₂ (BET = 2–3 m²/g). In the loose contact mode, the yttrium doping and loading have a minor or null affect on the activity, and the stabilising effect of the BET area due to zirconium doping prevails.     

Nature and conditions of formation of structural defects in zirconium(IV) oxide in the course of its preparation from zirconium hydroxide

The nature of paramagnetic defects in nanosized ZrO₂ samples prepared by the sol-gel method was studied by ESR. Conditions of formation of different centers (Zr³⁺, F centers, O^?, O ₂ ^? ) in ZrO₂ were elucidated. The Zr³⁺ and O^? centers arise in the course of thermal dehydration of Zr(OH)₄ under the conditions when the formation of a Zr-O-Zr bridging bond is hindered. The F centers are formed in ZrO₂ on heating in a reducing atmosphere or as a result of structural rearrangements accompanied by a decrease in the amount of lattice oxygen in the coordination surrounding of Zr(IV).     

Formation Mechanism of O2– Radical Anions in the Adsorption of NO + O2 and NO2 + O2 Mixtures on ZrO2 According to EPR and TPD Data

The effects of various factors on the formation of O₂ ^– radical anions in the adsorption of an NO + O₂ or NO₂ + O₂ mixture on ZrO₂ were studied. It was found that the thermal stability of the O₂ ^– species depends on the composition of the adsorbed gas. It was suggested that nitrogen oxide complexes on ZrO₂ centers are responsible for the formation of O₂ ^–. These centers are formed upon the treatment of the oxide in a vacuum; however, they are different from both coordinatively unsaturated Zr⁴⁺ cations (NO adsorption centers at 77 K) and Zr⁴⁺–O^––O^––Zr⁴⁺ centers, at which O₂ ^– are formed because of the adsorption of H₂ + O₂. Based on the experimental data, the mechanism of O₂ ^– formation in the adsorption of an NO + O₂ mixture is discussed.     

Mechanism of the Formation of O2? Radical Anions on CeO2 and (0.5–10)%CeO2/ZrO2 during the Adsorption of an NO-O2 Mixture

It is established by ESR that the adsorption of an NO + O₂ mixture at 20°C on oxidized CeO₂ (O₂, T = 400–700°C) produces radical anions O ₂ ⁻ located both on isolated Ce⁴⁺ cations (O ₂ ⁻ (1)) and in associated anionic vacancies (O ₂ ⁻ (2)). These species differ in thermal stability. For example, O ₂ ⁻ (2) decomposes at 20°C, while O ₂ ⁻ (1) decomposes at 50°C. Only O ₂ ⁻ (1) species are observed at −196°C in ZrO₂-supported CeO₂. In the case of NO + O₂ adsorption at 20°C, O ₂ ⁻ is stabilized on Zr⁴⁺ cations and decomposes at 270°C. Increasing the cerium oxide content of the ZrO₂ surface from 0.5 to 10% only partially inhibits the formation of O ₂ ⁻ -Zr⁴⁺. The Zr⁴⁺ cation is shown to possess a higher Lewis acidity than the Ce⁴⁺ cation, and the ionic bond in O ₂ ⁻ -Zr⁴⁺ complexes is stronger than that in O ₂ ⁻ -Ce⁴⁺ complexes. ESR, temperature-programmed desorption, and IR spectroscopic data for various adsorption complexes of NO on CeO₂ suggest that, in the key step of O ₂ ⁻ formation, free electrons appear on the surface owing to the conversion of adsorbed NO molecules into nitrito chelates on coordinately unsaturated ion pairs Ce⁴⁺-O ₂ ⁻ .__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 414–422.Original Russian Text Copyright © 2005 by Il’ichev, Shibanova, Ukharskii, Kuli-zade, Korchak.     

Methanol conversion over CuO supported on CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript>: An in situ IR spectroscopic study

The main reactions yielding hydrogen are the recombination of hydrogen atoms on copper clusters and methyl formate decomposition. Methyl formate results from the interaction between the linear methoxy group and the formate complex located on CuO. The source of CO₂ appearing in the gas phase is the formate complex, and the source of CO is methyl formate. The rates of methoxy group conversion and product formation over supports (ZrO₂, CeO₂, Ce_0.8Zr_0.2O₂) and copper-containing catalysts (5%Cu/CeO₂, 5%Cu/ZrO₂, 2%Cu/Ce_0.8Zr_0.2O₂, 2%Cu/Ce_0.1Y_0.1Zr_0.8) are compared. The dominant process in methoxy group conversion over the supports and copper-containing catalysts is methanol decomposition to H₂ and CO and to H₂ and CO₂, respectively. The methoxy group conversion rate is proportional to the H₂ and CO₂ formation rate and is determined by the concentration of supported copper.     

Unusual Approaches to the Preparation of Heterogeneous Catalysts and Supports Using Water in Subcritical and Supercritical States

The prospective ways of using water in sub- and supercritical states for the preparation of nanocrystal oxide catalysts Ce_0.5Zr_0.5O₂, Ce_0.1Y _x Zr_{0.9 – x} O₂, Zr_{1 – x} Y _x O₂, Zr_{1 – x} In _x O₂, La₂CuO₄, supported catalysts Pd/Rh/ZrO₂and Pd/Rh/TiO₂, and supports CeO₂, ZrO₂, TiO₂are discussed. The proposed technique is characterized by high productivity. It is also ecologically friendly and enables one to obtain multicomponent oxide catalysts with chemical and phase composition and properties that can be changed within large ranges. The physicochemical properties of sub- and supercritical water are discussed. A brief review of the present studies on the use of critical media in various physicochemical processes is given.     

Structure and surface properties of ZrO<Subscript>2</Subscript>, CeO<Subscript>2</Subscript>, and Zr<Subscript>0.5</Subscript>Ce<Subscript>0.5</Subscript>O<Subscript>2</Subscript> prepared by a microemulsion method according to X-ray diffraction,TPR, and EPR data

It was established by X-ray diffraction, TPR, and EPR that microemulsion (m.e.) synthesis yields the binary oxides ZrO₂(m.e.) and CeO₂(m.e.) and the mixed oxide Zr_0.5Ce_0.5O₂(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. ZrO₂(m.e.) and CeO₂(m.e.) are active in O₂⁻ formation during NO + O₂ adsorption, while CeO₂ is active during CO + O₂ 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 Zr⁴⁺ and Ce⁴⁺ coordinatively unsaturated cations and Me⁴⁺-O²⁻ pairs. O₂⁻ radical anions are stabilized in the coordination sphere of Zr⁴⁺ coordinatively unsaturated cations via ionic bonding, and in the sphere of Ce⁴⁺ cations, via covalent bonding. Ionic bonds are stronger than ionic-covalent bonds and do not depend on the ZrO₂ phase composition. Zr_0.5Ce_0.5O₂ 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 Zr⁴⁺ and Ce⁴⁺ cations in ZrO₂ and CeO₂, according to the order ZrO₂ > CeO₂ ≥ Zr_0.5Ce_0.5O₂. Neither TPR nor adsorption of probe molecules revealed Zr cations on the surface of the mixed oxide.     

Defect Clusters and Superstructures of ZrDissolved Ni1−xO

Ni_1−xO (x<0.001) powders, pure and mixed with pure ZrO₂or yttria–partially stabilized zirconia (Y-PSZ), were sintered and then annealed at 1573 and 1873 K for up to 300 h to investigate the dopant dependence of defect clustering in the Ni_1−xO lattice. Transmission electron microscopic observations coupled with energy X-ray analysis indicated that the dissolution of Zr⁴⁺(ca. 2.0 mol% with or without co-dopant Y³⁺< 0.3 mol%) but not Ni³⁺caused defect clustering, which was more rapid at 1873 than 1573 K and which preferred to nucleate at interfaces and dislocations. The paracrystalline distribution of defects was found to be nearly 3.5 and 2.5 times the lattice parameter of Ni_1−xO for Zr-doped and (Zr,Y)-codoped Ni_1−xO, respectively. The predominantly dissolved Zr⁴⁺cations, in octahedral sites with charge- and volume-compensating nickel and oxygen vacancies (i.e., Zr^oct□_nO_6−m□_m), could create local domains in which Ni³⁺should be expelled and, thus, in the vicinity the paracrystalline state and then the spinel Ni₃O₄could precipitate in local domains. The spinelloid, a superstructure of spinel with a relatively high Zr⁴⁺content (ca. 3.5 mol%), appeared only for the Ni_1−xO particles located at Y-PSZ grain boundaries.     

Yttria stabilized zirconia solid electrolyte surface modification with ZrO<Subscript>2</Subscript>, Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript> + 9 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> films

The surface of ceramic electrolyte ZrO₂ + 9 mol % Y₂O₃, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of ZrO₂, Y₂O₃, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing. The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO₂, Y₂O₃, and YSZ films to the polarization resistance of silver electrode was studied.     

Synthesis of garnet structured Li7+x La3Y x Zr2-x O12 (x = 0–0.4) by modified sol–gel method

Preparation of lithium garnet Li₇La₃Zr₂O₁₂ (LLZ) in cubic phase by solid state method requires high temperature sintering around 1,200 °C for 36 h in Al₂O₃ crucible with intermittent grinding. Synthesis of LLZ in cubic phase at lower temperatures by wet chemical methods was reported earlier, however that decompose at high temperature around 850 °C. In this work we report the systematic studies on synthesis of garnet structured electrolytes by modified sol–gel method by the simultaneous substitution of Li⁺ and Y³⁺ for Zr⁴⁺ according to the formulae Li_7+x La₃Y _x Zr_2-x O₁₂ (x = 0, 0.1, 0.2, 0.3 and 0.4). The present investigation revealed that the cubic garnet phase is obtained at much lower temperature for Li₇La₃Zr₂O₁₂ and the simultaneous increase of both Li⁺ and Y³⁺ in Li_7+x La₃Y _x Zr_2-x O₁₂ requires slightly higher sintering temperatures for the formation of cubic garnet phase. SEM micrographs of the Li_7+x La₃Y _x Zr_2-x O₁₂ (x = 0, 0.1, 0.2, 0.3 and 0.4) annealed at minimum sintering temperature required for the formation of cubic garnet phase revealed the increase in grain size and relatively dense structure with increase of x in Li_7+x La₃Y _x Zr_2-x O₁₂.     

Vacuum Ultraviolet Excited Photoluminescence Properties of Y2O2S：Eu^3＋,Bi^3＋ Phosphor

As an Hg-free lamp using phosphor, the Bi^3＋ and EH^3＋ co-doped Y2O2S phosphors were prepared and their luminescence properties under vacuum ultraviolet（VUV） excitation were investigated. The VUV photoluminescent intensity of Y2O2S：Eu^3＋ was weak, however, considerably stronger red emission at 626 nm with good color purity was observed in Y2O2S：Eu^3＋,Bi^3＋ systems. Investigation on the photoluminescence reveals that the strong VUV luminescence of Y2O2S：Eu^3＋,Bi^3＋ at 147 nm is mainly because the Bi^3＋ acts as a medium and effectively performs the energy transfer process： Y^3＋-O^2-→Bi^3＋→Eu^3＋, while the intense emission band at 172 nm is attributed to the absorption of the characteristic ^1So-^1P1 transition of Bi^3＋ and the direct energy transfer from Bi^3＋ to Eu^3＋. The Y2O2S：Eu^3＋,Bi^3＋ shows excellent VUV optical properties compared with the commercial （Y,Gd）BO3：Eu^3＋. Thus, the Y2O2S：Eu^3＋,Bi^3＋ can be a potential red VUV-excited candidate applied in Hg-free lamps for backlight of liquid crystal display.     

EPMA of interfaces applied to the solid oxide fuel cell

Chemical interactions at the phase boundaries of materials applied for the solid oxide fuel cell (SOFC) have been studied by EPMA. The chemical reactivity at the interface of La_y-xSr_xMnO₃/ZrO₂-Y₂O₃ is dependent on the stoichiometry (y) and the Sr content (x) of the perovskite. Typical reaction products (zirconates) and a diffusion zone in the ZrO₂–Y₂O₃ have been observed. The extension of cation release (Mn) is related to the increasing chemical activity of Mn oxide in the perovskite by the Sr substitution for La. The wettability of the metal/oxide interface in the anode cermet (Ni/ZrO₂–Y₂O₃) has been found to be influenced by chemical reactions resulting from the applied reducing atmosphere with high carbon activity. The disintegration of ZrO₂–Y₂O₃ in contact with molten Ni or Ni-Ti and Ni-Cr alloys leads to the redeposition of Y₂O₃-enriched oxides and also to Zr-rich intermetallic compounds and eutectics.     

Synthesis of Er3+:Y3Al5O12 and its effects on the solar light photocatalytic activity of TiO2–ZrO2 composite

The Er³⁺:Y₃Al₅O₁₂ as an upconversion luminescence agent, which can transform visible light into ultraviolet light, was synthesized by nitrate?Ccitrate acid and calcined method. Then, a novel photocatalyst, Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂, was prepared using ultrasonic dispersion and liquid boiling method. The samples were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). In succession, the degradation process of organic dye was monitored by UV?CVis spectrum and ion chromatography for verifying the photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂. The influences on its photocatalytic activity such as Ti/Zr molar ratio, heat-treated temperature, and time were studied. In addition, the influences of initial concentration, Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ amount, solar light irradiation time, and organic dye category on the photocatalytic degradation efficiency were also investigated. It was found the photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ was superior to Er³⁺:Y₃Al₅O₁₂/TiO₂ and Er³⁺:Y₃Al₅O₁₂/ZrO₂. Therefore, the Er³⁺:Y₃Al₅O₁₂/TiO₂?CZrO₂ is a useful photocatalytic material for the wastewater treatment duo to efficient utilization of solar light.     

Non-Oxidative Propane Dehydrogenation on CrOx-ZrO2-SiO2 Catalyst Prepared by One-Pot Template-Assisted Method

A series of CrO_x-ZrO₂-SiO₂ (CrZrSi) catalysts was prepared by a “one-pot” template-assisted evaporation-induced self-assembly process. The chromium content varied from 4 to 9 wt.% assuming Cr₂O₃ stoichiometry. The catalysts were characterized by XRD, SEM-EDX, temperature-programmed reduction (TPR-H₂), Raman spectroscopy, and X-ray photoelectron spectroscopy. The catalysts were tested in non-oxidative propane dehydrogenation at 500–600 °C. The evolution of active sites under the reaction conditions was investigated by reductive treatment of the catalysts with H₂. The catalyst with the lowest Cr loading initially contained amorphous Cr³⁺ and dispersed Cr⁶⁺ species. The latter reduced under reaction conditions forming Cr³⁺ oxide species with low activity in propane dehydrogenation. The catalysts with higher Cr loadings initially contained highly dispersed Cr³⁺ species stable under the reaction conditions and responsible for high catalyst activity. Silica acted both as a textural promoter that increased the specific surface area of the catalysts and as a stabilizer that inhibited crystallization of Cr₂O₃ and ZrO₂ and provided the formation of coordinatively unsaturated Zr⁴⁺ centers. The optimal combination of Cr³⁺ species and coordinatively unsaturated Zr⁴⁺ centers was achieved in the catalyst with the highest Cr loading. This catalyst showed the highest efficiency.     

Thermal analysis and epr studies of carbon black oxidation in the presence of copper loaded Y2O3-CeO2-ZrO2 catalyst

The activity of copper-free and copper-loaded 10Y₂O₃-10CeO₂-80ZrO₂ solid solutions towards carbon black combustion was studied using simultaneous thermogravimetric analysis and differential thermal analysis techniques coupled with gas chromatography. It was demonstrated that all studied catalysts lower the temperature of carbon black combustion. The selectivity of the catalytic reaction in CO₂ formation was 100%. The comparison of electron paramagnetic resonance (EPR) spectra of pure catalysts with those of the samples (catalysts mixed with carbon black) after catalysis allowed to evidence, despite of the strong oxidizing atmosphere, a thermal reduction by carbon of Fe³⁺ (impurities), Cu²⁺ and Zr⁴⁺ during the reaction. Moreover a new EPR signal appeared after catalytic test and was attributed to the presence of paramagnetic metal-carbon or/and metal-sulphur complexes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Selective oxidation of CO in excess hydrogen on copper—cerium-containing catalysts

Selective oxidation of CO that is in mixtures enriched in H₂ was studied to investigate catalytic properties of the 0.5—80% CuO/Ce_0.7Zr_0.3O₂ system. The catalysts were prepared by the combined decomposition of copper, cerium, and zirconyl nitrates at 300 °C. The systems studied are active and stable under mild conditions of the process (80—160 °C) and at high space velocities (to 100000 h^–1) of the reaction mixture (2% CO, 1% O₂, 40—50% H₂). With an increase in the CuO content in the catalysts up to 20%, the degree of CO removal achieves 60% (120 °C and V = 35000 h^–1) and further does not change appreciably. The contribution of oxygen participation into CO oxidation is virtually independent of the copper concentration in the sample and ranges from 65 to 75%. The dependences of the Arrhenius equation parameters for CO and H₂ oxidation on the catalyst composition were determined, which makes it possible to calculate the conversion of reactants and selectivity of CO conversion under the specified conditions of the process. The addition of CO₂ and H₂O (12—15%) to the reaction mixture decreases the catalyst activity and simultaneously increases the selectivity of CO oxidation to 100%. It is shown by the TPR and X-ray diffraction methods that the combined decomposition of the starting Cu²⁺, Ce³⁺, and ZrO²⁺ nitrates produces solid solutions of oxides with a high content of CuO. The reductive pre-treatment of fresh samples of the studied catalysts results in the destruction of the solid solution and formation of highly dispersed Cu particles on the surface of Ce—Zr—O. These particles are active in CO oxidation.     

Ce4+替代Pu4+的模拟固化体(Gd1-xCex)2Zr2O7+x的合成及结构演变

Gd₂Zr₂O₇中Gd具有很大的中子吸收截面, 其烧绿石结构-缺陷萤石结构的转变能较低, 使其成为理想的核废料固化基材. 使用硝酸盐为原料, 添加少量NaF作助熔剂, 在较低温度下(和传统高温固相反应相比), 合成了烧绿石型Gd₂Zr₂O₇. 以Ce⁴⁺模拟Pu⁴⁺, 研究了Gd₂Zr₂O₇对锕系核素的固化, 并合成了系列模拟固化体(Gd_1-xCe_x)₂Zr₂O_7+x (0≤x≤0.6). 采用粉末X射线衍射(XRD)对系列样品进行了表征. 结果表明: 随着x值的增大,样品从烧绿石结构向缺陷萤石结构转变, 且晶胞大小基本保持恒定, 但当x=0.6时, 衍射峰明显宽化, 晶格畸变比较严重, 晶格稳定性降低. 当x=1时, 即用Ce⁴⁺完全取代Gd³⁺进行合成, 不能得到Ce₂Zr₂O₈, 产物发生了相分离, 为四方结构的(Zr_0.88Ce_0.12)O₂和萤石结构的(Ce_0.75Zr_0.25)O₂的混合物. 模拟固化体的浸出率测试表明: 当x≤0.2时, 各元素浸出率均很低, 但当x≥0.4时, 各元素的浸出率明显升高, 说明以Gd₂Zr₂O₇作为固化Pu⁴⁺的基材, Pu⁴⁺掺入量不宜高于40%.