Showing papers on "Mixed oxide published in 2003"

Structural Characterization of CeO2−TiO2 and V2O5/CeO2−TiO2 Catalysts by Raman and XPS Techniques

Abstract: Structural characteristics of ceria−titania and vanadia/ceria−titania mixed oxides have been investigated using X-ray powder diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) techniques. The (1:1 mole ratio) mixed oxide was obtained by a coprecipitation method, and a nominal 5 wt % V2O5 was deposited over its surface by a wet impregnation technique. Both of the materials were then subjected to thermal treatments from 773 to 1073 K and were characterized by the above-mentioned techniques. The XRD results suggest that the CeO2−TiO2 mixed oxide calcined at 773 K primarily consists of poorly crystalline CeO2 and TiO2-anatase phases and that a better crystallization of these oxides occurs with increasing calcination temperature. The “a” cell-parameter values suggest some incorporation of titanium into the ceria lattice. Impregnation of vanadia on ceria−titania enhances the crystallization of CeO2 and TiO2 oxides. However, no crystalline V2O5 could be observed from XRD and R...

Reduction property and catalytic activity of Ce1-XNiXO2 mixed oxide catalysts for CH4 oxidation

Abstract: Ce 1− X Ni X O 2 oxides with X varying from 0.05 to 0.5 were prepared by different methods and characterized by XRD and TPR techniques. Ce 0.7 Ni 0.3 O 2 sample prepared by sol–gel method shows the highest reducibility and the highest catalytic activity for methane combustion. Three kinds of Ni phases co-exist in the Ce 1− X Ni X O 2 catalysts prepared by sol–gel method: (i) aggregated NiO on the support CeO 2 , (ii) highly dispersed NiO with strong interaction with CeO 2 and (iii) Ni atoms incorporated into CeO 2 lattice. The distribution of different Ni species strongly depends on the preparation methods. The highly dispersed NiO shows the highest activity for methane combustion. The NiO aggregated on the support CeO 2 shows lower catalytic activity for methane combustion, while the least catalytic activity is found for the Ni species incorporated into CeO 2 . Any oxygen vacancy formed in CeO 2 lattice due to the incorporating of Ni atoms adsorbs and activates the molecular oxygen to form active oxygen species. So the highest catalytic activity for methane combustion on Ce 0.7 Ni 0.3 O 2 catalyst is attributed not only to the highly dispersed Ni species but also to the more active oxygen species formed.

Synthesis and Characterization of MnO2-Based Mixed Oxides as Supercapacitors

Abstract: Mn/Pb and Mn/Ni mixed oxide were prepared at ambient temperature by reduction of KMnO4 with Mn, Pb, and Ni salts. This low-temperature approach provides amorphous structure of the active material. The specific capacitance of pure MnO 2 was estimated to be 166 F/g and increased to 210 and 185 F/g for Mn/Ni and Mn/Pb oxides, respectively. The carbon loading was optimized at 20 wt %. Based on a single electrode, the Mn/Ni mixed oxide showed a high rate capability of 3.12 Wh/kg at constant power discharge of 1 kW/kg.

Preparation and Characterization of Novel Hybrid Materials Formed from (Ti,Sn)O2 Nanoparticles and Polyaniline

Abstract: This paper describes the synthesis and characterization of new organic/inorganic hybrid materials formed from the mixed oxide (Ti,Sn)O2 nanoparticles and polyaniline (PANI). The preparation method is based on a sol−gel technique using titanium tetra-isopropoxide and tin tetrachloride as oxide precursors, and two synthetic routes to the hybrids formation were employed, based on the addition of aniline after or before the sol formation. Different amounts of aniline were used to verify this effect on the characteristics of the formed materials. Samples were characterized by thermal analysis, X-ray diffractometry, Raman, UV−vis, and FT-IR spectroscopy, transmission electron microscopy, cyclic voltammetry, and conductivity measurements. Results show that the different experimental routes are successful in producing hybrids formed by oxide nanoparticles or nanotubes and polyaniline in its conducting form, the emeraldine salt. There is little difference between the samples obtained by the two synthetic routes em...

Ni based mixed oxide materials for CH4 oxidation under redox cycle conditions

Abstract: The preparation, characterization and redox properties of Ni–Al–O and Ni–Mg–Al–O mixed oxides for CH 4 chemical looping combustion (CLC) is addressed in this study. Ni–Al–O samples having different Ni/Al ratios (0.5–2.25), prepared by coprecipitation, consist after calcination at 1000 °C of cubic NiO and NiAl 2 O 4 spinel. A similar phase composition is obtained for Ni–Mg–Al–O, with Mg partitioned in the two phases. The presence of NiAl 2 O 4 prevents the crystal size growth of NiO with respect to pure NiO; further limit of the sintering of the cubic oxide was observed in presence of Mg. Reduction of the samples by H 2 occurs in two steps, associated with reduction of Ni 2+ in NiO and NiAl 2 O 4 . Mg stabilizes Ni 2+ in both the cubic oxide and the spinel phase and improves regenerability upon repeated redox cycles. Temperature programmed reduction with CH 4 (CH 4 -TPR) experiments showed poor selectivity to CO 2 and H 2 O, being CO and H 2 the most abundant products. Also, formation of coke is observed over the samples. The same behavior is observed in CH 4 /O 2 pulse experiments; however, in the case of the Mg-containing system, coke formation can be avoided by co-feeding H 2 O along with CH 4 .

Raman and X-ray Photoelectron Spectroscopy Study of CeO2−ZrO2 and V2O5/CeO2−ZrO2 Catalysts

Abstract: The evolution and physicochemical characteristics of CeO2−ZrO2 and V2O5/CeO2−ZrO2 samples under the influence of thermal treatments from 773 to 1073 K were investigated using X-ray diffraction (XRD), BET surface area, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The CeO2−ZrO2 mixed oxide was synthesized by a coprecipitation method, and a nominal 12 wt % V2O5 was deposited over the calcined support (773 K) by a wet impregnation technique. The X-ray powder diffraction analysis suggests formation of a Ce0.75Zr0.25O2 cubic phase at 773 K. With increasing calcination temperature, better crystallization of this phase and incorporation of more zirconium into the ceria lattice were noted. The mean crystallite size and a cell parameter values obtained from XRD measurements strongly support this observation. The results further suggest that impregnation of vanadium oxide over the CeO2−ZrO2 surface accelerates the crystallization of Ce0.75Zr0.25O2 and incorporation of more zirconium into the ceria...

Propane Oxidation on MoVTeNbO Mixed Oxide Catalysts: Study of the Phase Composition of Active and Selective Catalysts

Abstract: Several phases reported as minor or major phases in the active MoVTeNbO catalysts have been prepared and investigated for the oxidation of propane into acrylic acid. Activity and selectivity of pure phases and mixtures of phases obtained either directly from synthesis or by co-grinding have been compared. The results obtained confirmed that the orthorhombic M1 phase is the most active and selective phase and is responsible for the major part of the efficiency of the best catalysts. However, they also clearly demonstrated that a synergism due to a cooperation between phases occurs, similar to that previously proposed between the M1 [(Te2O)M20O56] and M2 [(TeO)M3O9] phases for the ammoxidation of propane. The origin of this phase cooperation is discussed.

(Ti, Sn)O2 mixed oxides nanoparticles obtained by the sol-gel route

Abstract: This paper focuses on the preparation and characterization of a titanium−tin mixed oxide (Ti,Sn)O2 with anatase structure. The preparation method is based on a sol−gel technique using titanium tetr...

Silicon oxide in an iron(III) oxide matrix: the sol–gel synthesis and characterization of Fe–Si mixed oxide nanocomposites that contain iron oxide as the major phase

Abstract: The synthesis of Fe–Si mixed oxide nanocomposite materials in which the iron(III) oxide is the major component is described. In a typical synthesis, the iron oxide precursor, FeCl3 · 6H2O, was mixed with a silica precursor, tetramethyl- or tetraethylorthosilicate, in ethanol and gelled using an organic epoxide. The composition of the resulting materials was varied from Fe/Si (mol/mol)=1–5 by adjusting the amount of silica precursor added to the FeCl3 · 6H2O solution. Further processing of the gels in supercritical CO2 resulted in monolithic, porous aerogel nanocomposite materials with surface areas ranging from 350–450 m2/g. The bulk materials are composed of iron(III) oxide/silica particles that vary in size from 5–20 nm depending on the epoxide used for gelation. Iron(III) oxide and silica dispersion throughout the bulk material is extremely uniform on the nanoscale. The synthesis method presented is general for the synthesis of several other metal oxide/silicon oxide nanocomposite materials.

Alumina–titania binary mixed oxide used as support of catalysts for hydrotreating of Maya heavy crude

Abstract: Three different methods are applied to prepare alumina–titania binary mixed oxide supports. These supports are used to prepare catalysts for hydrotreating of Maya heavy crude. Sequential incipient wetness and co-impregnation techniques were employed for preparation of catalysts. Ammonium heptamolybdenum was used as precursor for MoO 3 . Catalysts are characterized by XRD, TPR and pore size distribution. Hydrodemetallation (HDM), hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and asphaltene conversion (HDAsp) reactions are studied on these catalysts. One reference catalyst is also taken for comparison. Coke and metals depositions on spent catalysts are measured. Catalyst deactivation rate is also studied. A combined method of urea hydrolysis and pH variation is suitable to prepare bigger size of pore diameter and more pore volume support. XRD results indicate that prepared alumina–titania oxides are amorphous or very poor crystalline in nature. Very complex nature of TPR profiles is observed. Two catalysts (C and D) show very high activities and also give very good stability compared to reference catalyst. We observe an average correlation between pore diameter of catalyst with HDM and HDAsp conversions. It indicates that bigger pore diameter catalyst is suitable for removal of metals and asphaltenes, but bigger pore size is not only criterion to show good HDM activity. Total pore volume is also an important parameter in this regard. Enhancement of activities is observed on P containing catalyst. Coke is deposited on the catalyst pore mouth and it caused a drastic reduction of specific surface area of spent catalyst. Coke deposition is more on the catalyst having bigger pore diameter. We also observe that rate of V removal is higher than rate of Ni removal.

Strong chemical interaction between PdO and SnO2 and the influence on catalytic combustion of methane

Abstract: Several palladium-tin oxide (PdO-SnO 2 ) catalysts were prepared by the impregnation (PdO/SnO 2 ) and co-precipitation (PdO-SnO 2 ) methods. Among the catalysts tested, the SnO 2 -supported 11 wt.% PdO catalyst prepared by the impregnation method showed the highest conversion at low temperatures. The reduction and adsorption properties of PdO/SnO 2 were quite different from those of PdO/Al 2 O 3 and PdO/ZrO 2 . X-ray diffraction (XRD) of these catalysts revealed that 10 nm PdO particles were supported on SnO 2 for the impregnated catalysts, while the co-precipitated catalysts were composed of uniform PdO-SnO 2 mixed oxide particles. Even at room temperature, the PdO particles in PdO/SnO 2 were easily reduced to metallic Pd and absorbed H 2 with the H 2 /Pd weight ratio of 0.3%. In both PdO/SnO 2 and PdO-SnO 2 samples, adsorption of CO was significantly suppressed because of the interaction between Pd and SnO 2 ; the metal surface area was difficult to estimate by the CO pulse technique.

Steam reforming of CH4 over supported Ni catalysts prepared from a Mg–Al hydrotalcite-like anionic clay

Abstract: spc-Ni/MgAl (spc: solid phase crystallization method) catalysts have been prepared from Mg–Al hydrotalcite-like compounds as the precursors and tested for steam reforming of CH4 into synthesis gas. The precursors based on [Mg(II)1−xAl(III)x(OH)2]x+(CO3−)x·mH2O, in which a part of Mg(II) ions were replaced by Ni(II) ions, were prepared by co-precipitation method, thermally decomposed and reduced to form spc-Ni/MgAl catalyst. Surface areas of spc-Ni/MgAl catalysts were always high at around 150 m2 g-cat−1. Ni(II) ions first substituted a part of the Mg(II) sites in the Mg–Al hydrotalcite-like compounds and then incorporated in the rock-salt type Mg–Ni–O solid solutions in the mixed oxide after the decomposition. The dispersion of Ni was thus repeatedly enhanced during the spc-preparation, resulting in the formation of highly dispersed Ni metal particles after the reduction. The activity of spc-Ni/MgAl catalyst was high when Ni/Mg was larger than 0.2, and the most suitable ratio of Mg/Al was 1/3. When the catalysts were tested in the steam reforming of CH4, spc-Ni0.5/Mg2.5Al showed high CH4 conversion following thermodynamic equilibrium even at a high space velocity of 9×105 ml h−1 g-cat−1, followed by imp-Ni/Mg3Al-aq prepared by impregnation of Mg–Al mixed oxide in aqueous solution. It is considered that, during the preparation of imp-Ni/Mg3Al-aq, surface reconstitution of the Mg–Al hydrotalcite layered structure took place by a “Memory Effect” of the hydrotalcite, resulting in the high dispersion of Ni metal particles. When spc-Ni0.5/Mg2.5Al was tested in the steam reforming of CH4, no deterioration in the catalytic activity was observed for 600 h of reaction time even under a low steam to carbon ratio of 1.6, while a commercial Ni/α-Al2O3 catalyst showed a clear decline in the activity. The CH4 conversion as well as the distribution of products followed thermodynamic equilibrium during the reaction for 600 h. It is concluded that spc-Ni0.5/Mg2.5Al is a hopeful candidate as a catalyst for the production of H2 for polymer electrolyte fuel cells.

Propane Selective Oxidation Over Monophasic Mo–V–Te–O Catalysts Prepared by Hydrothermal Synthesis

Abstract: Two distinct phases, orthorhombic and hexagonal, of Mo–V–Te–O mixed oxide catalysts were prepared separately by the hydrothermal synthetic method and solid-state reaction, and these catalysts were tested for propane selective oxidation to acrylic acid. The hydrothermally synthesized orthorhombic phase of the Mo–V–Te–O catalyst showed high activity and selectivity for the oxidation of propane into acrylic acid. This catalyst also showed extremely high catalytic performance in the propene oxidation, producing acrylic acid in a high yield. The hexagonal Mo–V–Te–O catalyst was formed via the solid-state reaction between the orthorhombic Mo–V–Te–O and α-TeVO4. This phase showed poor activity to both propane and propene oxidations, although the hexagonal phase was constructed with the octahedra of Mo and V similar to the orthorhombic phase. Reaction kinetics study over the catalyst with orthorhombic structure revealed that propane oxidation was of first order with respect to propane and nearly zero order with respect to oxygen, suggesting that the rate-determining step of the reaction is C–H bond breaking of propane to form propene. Structural effects on the catalytic oxidation performance were discussed.

Synthesis of Molybdenum and Vanadium-Based Mixed Oxide Catalysts with Metastable Structure: Easy Access to the MoVNbTe(Sb)Ox Catalytically Active Structure Using Reductant and Oxoacid

Abstract: This work presents a simple synthesis route for MoVNbTe(Sb)Ox with the metastable structure that is catalytically active for the selective oxidation of light alkanes. The addition of an oxoacid to the partially reduced raw material mixture assisted in the formation of the active structure around 600 °C in an O2-excluded atmosphere. This simple synthesis using a reductant and oxoacid is remarkable since it allows a combinatorial approach to diversify Mo- and V-based mixed oxides such as catalytic materials.

Study of the redox behaviour of high surface area CeO2–SnO2 solid solutions

Abstract: Molten alkali metal nitrites or nitrates and co-precipitation methods were used to prepare CeO2, SnO2 and Ce0.5Sn0.5O2 solid solutions with high surface areas. In the case of the single oxides prepared by the molten salt method, the use of KNO3 leads to better crystallised solids than with KNO2, but on the opposite with higher particle sizes and lower BET surface areas. The same effect was observed for the preparation of the mixed oxides with different resulting structures. With KNO3, the mixed oxide appears as a mechanical mixture of the single oxides, whereas with KNO2, a mixture of amorphous SnO2 and of solid solution with a specific surface area (SSA) of 100 m2 g−1 has been synthesised, but without evidence of Ce2Sn2O8 pyrochlore formation. The solid prepared by co-precipitation is also well dispersed. Its amorphous structure by X-ray diffraction (XRD) analysis does not allow to conclude to the formation of a solid solution. TPR experiments with hydrogen have shown a beginning of reduction at lower temperature in presence of the solid solution compared to the mechanical mixture of the single oxides. An improved reducibility was also observed with the oxide prepared by co-precipitation, which is in favour of a solid solution formation also in this case. Therefore, the resulting hydrogen consumption obtained when reducing the solid solutions at 450 °C is very high and the oxygen storage capacities (OSCs) reach about 1 mmol O2 g−1, value higher than those obtained with ceria-zirconia solid solutions. The OSC values were confirmed by oxygen chemisorption on the reduced solid between 25 and 450 °C. The full recovery of the initial solid solution was shown by XRD analysis and a second redox cycle has demonstrated the reversibility of the redox properties at this temperature.

TiO2–SiO2 supported hydrotreating catalysts: physico-chemical characterization and activities

Abstract: Hydrotreating of model molecules over high specific surface area (SSA) Co(Ni)Mo/TiO 2 –SiO 2 mixed oxide supported catalysts has been investigated in a micro-catalytic reactor at 400 °C and atmospheric pressure. Activity studies are carried out for thiophene hydrodesulfurization (HDS) and 1-cyclohexene hydrogenation (HYD). The effect of support composition, molybdenum content (2–14 wt.% Mo) and promoters contents (1–5 wt.% Co or Ni) is examined. Supported catalysts are characterized by BET specific surface area, X-ray diffraction (XRD), pore volume, zero point charge (ZPC) and low temperature oxygen chemisorptions (LTOC). Sulfided catalysts showed wide range of activity variation with support composition which relishes that molybdenum sulfided active phases strongly depend on the nature and composition of support. LTOC and catalytic activity results showed similar trend with the effect of molybdenum variation indicating that the number of anion vacancies varies with variation of MoS 2 phases. The highest activities were observed at 8 wt.% Mo loading and after that activity decreases with decreasing the anionic vacancies. The characterization results of XRD, ZPC and LTOC are well agreed about the Mo monolayer formation. Incorporation of TiO 2 with SiO 2 alters the nature of weak interaction of active phases with SiO 2 support, and overcome it through poor dispersion on the support surface. Therefore, TiO 2 counterpart plays a role to provide high intrinsic activity and generate favorable morphology of MoS 2 phases and metal support interaction.

Vapor-phase Beckmann rearrangement of cyclohexanone oxime over B2O3/TiO2-ZrO2

Abstract: Pure TiO 2 , ZrO 2 and TiO 2 -ZrO 2 mixed oxides with various compositions were prepared by the co-precipitation method. Catalysts containing 12 wt.% boria were prepared using these oxides and their catalytic performance for vapor-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam was determined. With increasing zirconia content in the mixed oxide, the specific surface area and the temperature of the phase transformation increased; maximum values were obtained for a mixed oxide having a Ti and Zr molar ratio of 1/1. XRD results indicated that TiO 2 -ZrO 2 became amorphous after calcination at 500 °C if neither the content of TiO 2 nor that of ZrO 2 was less than 25%. The yield of lactam increased with increasing zirconia content in mixed oxide and reached a maximum value for the B 2 O 3 /TiO 2 -ZrO 2 (1/1) catalyst. With further increase in zirconia content, the lactam yield decreased; the lowest value was observed for the pure ZrO 2 -supported catalyst. The acidic property and the pore characteristics of the catalyst were key factors that affected its performance. The influences of the operating parameters on the performance of B 2 O 3 /TiO 2 -ZrO 2 (1/1) catalyst were also investigated.

Nanogold on powdered cobalt oxide for carbon monoxide sensor

Abstract: Powders of Co3O4 and Au/Co3O4 were used as sensing material for a solid electrolyte sensor of carbon monoxide. Prepared powders were deposited on the anode of a galvanic cell using a mixed oxide electrolyte of 5% Y2O3 and 95% ZrO2. By comparison with other metal oxides, Co3O4 displayed good response time and high sensitivity at a moderate temperature of 130 °C. Impregnation of nano-sized crystallites of gold improved the signal of the fabricated sensor. The required operation temperature is limited by the conductivity of the solid electrolyte in the cell.

Pt/Ce0.68Zr0.32O2 Washcoated Monoliths for Automotive Emission Control

Abstract: A three-way model catalyst has been prepared with 0.58 wt% Pt on Ce 0.68 Zr 0.32 O 2 mixed oxide washcoated on a ceramic monolith. Conditions of the washcoating procedure, i.e., powder size distribution and acidic nature of the slurry, have been optimized. The activity on simultaneous elimination of NO, C 3 H 6 , and CO of the prepared monolithic catalyst has been determined, fresh and after submitted to mild and severe reducing-oxidizing thermal treatments. Changes in activity have been related with the role of platinum and ceria-zirconia mixed oxide in the reaction environment. The effect of aging under severe oxidation at higher temperature has also been related to the reduction of textural properties of the catalyst. The efficiency of the prepared catalyst was compared with three-way catalyst behavior of two commercial ceria-based monolithic catalysts with similar platinum contents and washcoat percentages, describing the advantages of using ceria-zirconia mixed oxides instead of CeO 2 /Al 2 O 3 to improve stability and oxygen storage capacity.

The “one-pot” synthesis of 4-methyl-2-pentanone (methyl isobutyl ketone) from acetone over PdCu catalysts prepared from layered double hydroxides

Abstract: Supported PdCu catalysts prepared from layered double hydroxides (LDHs) as precursors were evaluated in the gas phase reaction of acetone with hydrogen to methyl isobutyl ketone (MIBK). Two series of catalysts containing ca. 0.2 wt.% Pd and various amounts of Cu (Cu/Pd molar ratio of ca. 0.25, 0.5 and 1) were elaborated according to different methods. One series of precursors was obtained by impregnation of calcined Mg(Al)O mixed oxide with heterobinuclear PdxCu1−x acetylacetonates. A second series of precursors was synthesized by coprecipitation of Mg/Pd/Cu/Al LDHs. After calcination, both series were reduced at 473 K. The extends of basic, acid and metal functions were evaluated through microcalorimetric adsorption of CO2, TPD of NH3 and TPR of H2. It was found that the multifunctional transformation of acetone to MIBK was rate determined by the basic function. However, the way by which the catalysts were prepared, impregnation or coprecipitation, controls the extend of hydrogenated by-products, isopropyl alcohol and 4-methyl-2-pentanol. The extensive dilution by migrating MgAlOx species onto the metallic particles makes the coprecipitated catalysts highly selective by decreasing selectively the rate of CO bond hydrogenation.

Catalytic hydrogen transfer from 2-propanol to cyclohexanone over basic Mg–Al oxides

Abstract: Magnesium–aluminium mixed oxides in mole ratios from 2 to 4 were obtained by thermal decomposition of layered double hydroxides (LDHs) as precursors. The effect of the Mg/Al ratio on the structure and surface properties of the resulting oxides was studied by using various instrumental techniques including X-ray diffraction (XRD), thermogravimetric analyses (TGA), MAS NMR, X-ray photoelectron spectroscopy (XPS) and gas adsorption–desorption, and so was their influence on the catalytic activity of the solids in the hydrogen transfer from 2-propanol to cyclohexanone. The results were compared with those for a pure MgO oxide and the Mg–Al mixed oxide obtained from the LDH with an Mg/Al ratio of 2 was found to provide the best catalytic activity. The influence on catalytic activity of other experimental variables including the pH of the medium used to synthesize the precursor LDHs, the temperature employed to prepare the Mg–Al oxides and the amount of catalyst used was also examined. Catalyst recycling tests were also conducted. Based on the results, a mechanism is proposed for the overall catalytic hydrogen transfer.

Spectroscopic Characterization of Heterogeneity and Redox Effects in Zirconium−Cerium (1:1) Mixed Oxides Prepared by Microemulsion Methods

Abstract: Two Zr−Ce (1:1 molar ratio) mixed oxide specimens, made by the same microemulsion method from different cerium precursor salts (samples ZC1 and ZC2), have been studied by a combination of physicochemical techniques. After calcination at 773 K (high surface area materials HS: SBET = 96 ± 1 m2 g-1) both samples present similar characteristics in XRD, Raman and TEM (pseudocubic phase t‘ ‘), and XPS/Ar+-etching experiments. This latter evidence for those materials gives a similar moderate surface enrichment in cerium and a surface anion vacancy concentration (judged from O(1s) peak shifts) lower than in CeO2; the latter effect suggests an easy diffusion of vacancies to bulk or subsurface regions. Only EPR of adsorbed superoxide species detects a difference between both samples, evidencing in ZC2−HS the presence of small, more reducible Ce-rich bidimensional patches over a Zr-richer substrate. According to XPS/Ar+ etching profiles, by calcination at 1173 K (LS materials; SBET < 8 m2 g-1), surface segregation o...