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Copper-iron mixed oxides with Fe/Cu molar ratios ranging from pure CuO to Fe2O3 were synthesised by a low temperature co-precipitation method, and tested in the CO-PROX reaction. The extensive characterization performed by means of different techniques showed the progressive variation of physical and chemical properties including composition, texture, structure and reducibility of the prepared oxides. Rietveld analysis of X-ray diffraction data, XPS and Raman spectra, and especially TEM study revealed the formation of CuFe2O4. All the samples were more active and selective below 200 °C than a commercial Pt/Al2O3 catalyst used as a reference. In particular, the catalyst having a 2 Fe/Cu molar ratio, corresponding to the cuprospinel stoichiometry, exhibited the best performance with a 76% conversion and a 60% selectivity at 125 °C, operating with 50% of H2 in the gas stream, being relatively stable in long-term time-on-stream experiments. On the contrary, pure CuO rapidly deactivated in the course of reaction at 150 °C. Differences in catalytic stability were related to a promoting effect of iron in the mixed oxide which makes copper more resistant to full reduction.

Clay honeycomb monoliths (MC) washcoated by pillared clay (PILC) obtained from the same starting material were used as support of manganese catalysts for the complete oxidation of acetone. Using the same clay for extrusion and pillaring processes intended to optimize the catalyst preparation respect to previous similar studies through raw materials saving, with subsequent local clay valorization, and washcoat adherence enhancement due to higher chemical affinity with the monolith substrate. To evaluate the influence of the PILC presence on the catalytic behaviour, two other non-coated monolith catalysts were prepared as references, having different loads of manganese as function of the impregnation cycles number applied, either one (Mn/MC) or two (Mn2/MC). All the catalysts were characterized by TGA, XRD, XRF, N2 physisorption and SEM. The catalytic tests used acetone as a VOC model molecule. The results indicated that the PILC coating (Mn/PILC/MC) led to a higher percentage of Mn2O3 (7 wt%) compared to Mn/MC (1 wt%). Moreover, the PILC-washcoated sample exhibited better performance in the acetone oxidation than Mn2/MC regardless this sample had higher Mn2O3 loading (11 wt%). This effect was related to the active phase crystal characteristics as well as to the textural properties induced by the PILC washcoating.

Carbon integral honeycomb monoliths with good performance in the thermocatalytic decomposition of methane were deeply characterized to understand the differences of behaviour resulting from their different pre-treatment. In particular three types of carbon monoliths were investigated, just carbonized, and activated with and without pre-oxidation. Advanced techniques such as X-ray Diffraction with Rietveld analysis, X-ray Photoelectron Spectroscopy and Scanning-Transmission Electron Microscopy with HAADF and EELS analysis were applied to unveil the origin of their differences which could not be correlated with the textural properties nor with the surface groups functionality. Particular attention was paid to the initial defects concentration and the nature of the carbon produced during the reaction, not finding either clear differences between the three types of monoliths studied. On the contrary the simply activated monoliths, with the highest activity, seemed to have higher content of a relatively amorphous graphite in which more actives sites for the reaction must be present. They also exhibited higher initial percentage of carbon atoms on the surface and a relative increase of C–C bonds after reaction. In addition the interaction between the carbonaceous phase and some of the phases of the clay used to extrude the starting coal could influence the carbon reactivity.

Two commercial high BET surface areas CeO2 are characterized, as received and after calcination at different temperatures, to better understand the relationship between reducibility and micro- and nanostructure. Combination of TPR data, Rietveld analysis of XRD diagrams and HREM/HAADF-STEM suggest that the nano-particles are responsible for Ce4+ reduction in the moderate temperature range. Results obtained in this work show that previous models based on kinetic and theoretical analysis can be fully supported by morphological characterization. This study unveils the key parameters that must be known in order to select appropriate commercial ceria samples.

A novel Co (15 wt.%)/La-modified-CeO2 catalyst was prepared for the oxidation of toluene and ethyl acetate, showing lower light-off temperature (around 20–40 °C) than that of a Pt (3 wt.%)/La-CeO2 catalyst under the same experimental conditions. Upon washcoating onto cordierite it was still more active than the noble metal reference. The activity remained stable even after 80 h of reaction. Adherence tests indicated a 98% stability of the washcoat, while SEM–EDS study evidenced its homogeneous distribution on the cordierite. ICP analysis and X-ray diffraction demonstrated that the composition and cobalt phase (Co3O4) of the powdered catalyst were the same in the washcoat. Moreover textural properties improved according to N2 physisorption studies due to inclusion of colloidal alumina in the slurry.

Coatings of zirconium oxide were deposited onto three types of stainless steel, AISI 316L, 2205, and tool steel AISI D2, using the ultrasonic spray pyrolysis method. The effect of the flux ratio on the process and its influence on the structure and morphology of the coatings were investigated. The coatings obtained, 600 nm thick, were characterized using x-ray diffraction, scanning electron microscopy, confocal microscopy, and atomic force microscopy. The resistance to corrosion of the coatings deposited over steel (not nitrided) and stainless steel nitrided (for 2 h at 823 K) in an ammonia atmosphere was evaluated. The zirconia coating enhances the stainless steel’s resistance to corrosion, with the greatest increase in corrosion resistance being observed for tool steel. When the deposition is performed on previously nitrided stainless steel, the morphology of the surface improves and the coating is more homogeneous, which leads to an improved corrosion resistance.

Two alumina-supported Ce/Pr mixed oxides, with different alumina promoters, La and Si, have been investigated in this paper. A gradual decrease of the Oxygen Storage Capacity (OSC) was observed after reducing the samples at progressively higher temperatures. However, depending on the nature of the alumina promoter, the temperature at which the loss of OSC started to be evident changed, being higher in the La-doped sample. A structural characterization study by X-ray diffraction (XRD) of the samples submitted to different reduction and reoxidation treatments in a range of temperatures was performed. From this study a correlation between the nature of the observed phases, the alumina promoter, and the deactivation behaviour could be stated. FTIR study is of particular interest because the observed correlation between the reduction degree and the position and intensity of the FTIR band is altered when deactivation phenomena appear.

In this study a simple method to activate clay honeycomb monoliths is proposed. It consists of mixing the clay with coal before the extrusion, and further removing the coal from the monolith by heating under air at the lowest possible temperature. This procedure is an easy, non-destructive and economical way of activating clay monoliths by an enhancement of their porosity. Characterization techniques such as N 2 physisorption, mercury porosimetry and scanning electron microscopy (SEM) showed an improvement of the clay textural properties as a consequence of carbon burning. X-ray diffraction with Rietveld analysis indicated that no significant structural modification of the clay took place. Axial crushing tests demonstrated that there was no worsening of the mechanical strength in the resulting activated monoliths. Finally, investigation of their performance in methylene blue adsorption experiments suggested that the route here proposed could be an alternative to acid activation methodologies. In particular, the results are interesting for those applications in which combination of the honeycomb monolithic design and the improvement of macroporosity may represent an advantage.

A series of catalysts consisting in Cu or Mn supported on lab-scale carbon-based honeycomb monoliths, which have been previously prepared following an original methodology, have been investigated in the low-temperature selective catalytic reduction of NO with NH 3 . Special attention has been paid to the effect of changing different preparative variables for the incorporation of the active phase: way of introducing the metal, concentration of the precursor solution and time of contact with the monoliths in the case of impregnation, use or not of a chemical pre-treatment of the support, and the final drying procedure. Complementary techniques employed for the chemical, textural and structural characterisation have revealed significant differences between the catalysts depending on their preparative procedure.

In this study, we have investigated the redox deactivation of a Ce/Pr mixed oxide supported on modified alumina. Two samples have been prepared by using silica- or lanthana-modified alumina as supports: 25% Ce 0.8 Pr 0.2 O 2-x /Al 2 O 3 -SiO 2 and 25% Ce 0.8 Pr 0.2 O 2-x /Al 2 O 3 -La 2 O 3 . The redox behavior was studied by reduction of the samples at selected temperatures, from 200 to 900 °C. Oxygen Storage Capacity (OSC) of reduced samples was measured by their reoxidation at 200 °C. The reduction degree attained by the supported mixed oxide, after reduction at temperatures up to 800 °C, increases in parallel for both samples. However, at 900°C, there is a decrease of OSC, which is moderate for silica-modified sample, while for lanthana-modified catalyst, the OSC is almost negligible. XPS analysis of the fresh samples shows that the redox state of cerium cations close to the surface is mainly +4, while praseodymium appears always as Pr 3+ . Samples reduced at different temperatures were also investigated by XPS. In the case of silica-modified alumina reduced at 900 °C, significant amounts of Ce 4+ can still be detected, which is in good agreement with the OSC value observed at that temperature. However, lanthana-modified sample reduced at 800 °C shows an important amount of Ce 3+ , being the only oxidation state observed for cerium after reduction at 900 °C. This is in good agreement with the strong drop in OSC observed for this latter sample, which can be thus attributable to the trapping of trivalent cations by the alumina, forming a stable perovskite-like aluminate, LnAlO 3 , as confirmed by X-Ray Diffraction (XRD).

The evolution of the ceria-praseodymia mixed oxide promoter throughout the successive steps involved in the preparation of a 3% Rh/25% Ce 0.8 Pr 0.2 O 2-x /Al 2 O 3 - 3.5% SiO 2 catalyst is studied with the help of X-ray diffraction (XRD), spatially resolved electron energy loss spectroscopy (EELS), XPS, and thermal programed desorption (TPD) techniques. Incipient wetness impregnation has been used to obtain the appropriate loading of this promoter. As revealed by XRD, EELS, and XPS data, the alumina-supported CeO 2 -PrO 2-x mixed oxide sample consisted of a bimodal distribution of the particles of the promoter. XRD shows two fluorite-like phases: cerium-rich particles with a mean crystallite size greater than 6 nm and smaller praseodymium-rich crystals, about 3.5 nm size. Surface Ce/Pr ratio obtained by XPS was consistent with a higher dispersion of the praseodymium-rich oxide particles. The final Rh catalyst was prepared in a second step, by impregnation of the CePrO x /Al 2 O 3 system with an acidic solution of Rh(NO 3 ) 3 . The low pH of this solution is responsible for further modifications of the lanthanide oxides distribution. Thus, there is a redispersion of the praseodymium-rich phase, which is evidenced by EELS and XPS data. Likewise, CO 2 desorption from samples exposed to the atmosphere is consistent with an enhanced basicity of the sample due to the increase of Pr 3+ content at the surface of the catalyst. The observed changes on the nanostructure of the mixed oxide promoter can be attributable to a partial dissolution of the oxide, selectively leaching Pr 3+ cations from the lattice, which are finally deposited as small particles after the drying steps of the preparation.

Textural, structural and adsorptive properties of some Moroccan clays were investigated. The minerals were used as raw material for extrusion of honeycomb monoliths. Adsorption and desorption tests were performed with selected model pollutants such as volatile organic compounds (VOCs). The clays have been chosen, apart from their abundance and price, on the basis of successful extrusion as integral lab-scale honeycomb monoliths. The obtained monoliths have been subjected to measurements of the mechanical strength.

The surface basicity of pure ceria is strongly enhanced by the presence of the supported La2O3, the effect being very much influenced by the calcination temperature. X-ray diffraction (XRD), Raman spectroscopy, and La 3d5/2 XPS data for the different samples show a progressive incorporation of La3+ into the ceria lattice as the calcination temperature is increased. This structural change is considered to be responsible for the modifications that occurred in the basicity of the lanthana-modified ceria samples as revealed by temperature-programmed desorption-mass spectrometry (TPD-MS) of pre-adsorbed CO2. Copyright © 2006 John Wiley & Sons, Ltd.

X-ray diffraction with Rietveld analysis, EDS, HREM, and CO oxidation experiments have been used to study the nanoscale evolution with reduction temperature of a Pd/Ce0.8Tb0.2O2-x/La2O3−Al2O3 catalyst. Up to 700 °C, both Pd and the Ce0.8Tb0.2O2-x mixed oxide are present as nanosized particles that are well-dispersed over the La-modified alumina support. After reduction at 900 °C, severe sintering of the metallic Pd particles occurs, along with the formation of a perovkite phase LnAlO3 with variable content of trivalent lanthanide ions (Ln3+ = La3+, Ce3+, and Tb3+). Parallel deactivation of the catalyst for the CO oxidation reaction is observed upon increasing reduction temperature.

N 2 adsorption at 77 K, temperature-programmed desorption (TPD), X-ray and neutron diffraction, and high-resolution electron microscopy (HREM) were used to characterize a Ce 0.8 Tb 0.2 O 2-x /La 2 O 3 -Al 2 O 3 oxide. This research shows that the supported cerium/terbium mixed oxide has good thermal stability up to 700 °C under H 2 (5%)/Ar and above this temperature in air or inert atmosphere. A combination of HREM and hydrogen chemisorption is shown to be a good method for estimating the dispersion of the supported cerium/terbium mixed oxide. The parallel study of its structural evolution also provides some interesting data on the deactivation of the supported Ce 0.8 Tb 0.2 O 2-x by reaction with the supporting alumina at 900 °C under H 2 (5%)/Ar and the formation of a LnAlO 3 perovskite phase.

Benzene hydrogenation and n -butane hydrogenolysis reactions have been tested on a series of Rh/La 2 O 3 /SiO 2 catalysts, their catalytic properties being compared with those of a Rh/SiO 2 sample studied as reference. This investigation has revealed that both activity and selectivity can be controlled by the procedure followed to prepare the catalysts. In particular, the influence of preparative conditions such as the lanthana loading, method of introduction of the metal and promoter (either consecutive or by co-impregnation) and temperature of calcination (873 or 1173 K) of the intermediate La 2 O 3 /SiO 2 phase onto which the noble metal is later deposited, have been analyzed. The differences in the catalytic behavior have been correlated with the La 2 O 3 /SiO 2 interactions, leading to a different degree of surface hydroxylation and different Rh particle crystallinity.

A methodology based on reoxidation at 298 K with O2(5%)/He pulses followed by quantitative TPO runs allowed us to study the redox state reached by CeO2 and Ln3+ -containing ceria‐based mixed oxide samples Ln3+:La3+ or Y3+) after their reduction in a flow of hydrogen. The temperature range covered in the reduction treatments was from 623 up to 1223 K. During the severe reduction treatments hexagonal sesquioxide phases segregate from all the samples. The reduction temperature at which segregation occurs follows the trend La/Ce < Y/Ce < CeO2. The TPO and H2-TPD traces of reduced samples which showed evidence of segregation in XRD exhibit characteristic features which can also be used as an indication of this effect. The discussion is focussed on the overall and detailed understanding of the reoxidation process and on the analysis of the H2-TPD profiles.

The present paper deals with the preparation and characterization of La/Ce mixed oxides, with La molar contents of 20, 36 and 57%. We carry out the study of the structural, textural and redox properties of the mixed oxides, comparing our results with those for pure ceria. For this aim we use temperature programmed reduction (TPR), temperature programmed desorption (TPD), nitrogen physisorption at 77 K, X-ray diffraction and high resolution electron microscopy. The mixed oxides are more easy to reduce in a flow of hydrogen than ceria. Moreover, in an inert gas flow they release oxygen in higher amounts and at lower temperatures than pure CeO2. The textural stability of the mixed oxides is also improved by incorporation of lanthana. All these properties make the ceria–lanthana mixed oxides interesting alternative candidates to substitute ceria in three-way catalyst formulations.

The combined application of chemical techniques and HREM shows that platinum deactivation in Pt/CeO2 catalysts steadily increases with the reduction temperature (Tr: 473–1173 K). Though no suppression of the H2 adsorption was observed, the TPD-H2 traces indicate the occurrence of significant chemical changes with Tr. As revealed by HREM, the metal decoration starts at Tr: 973 K, a temperature well above those at which the chemical effects can be observed.

This work reports on the HREM study of a series of Rh/CeO 2 catalysts reduced at temperatures ranging from 623 to 1173 K. Computer simulation and digital processing techniques were also used to arrive at a finer interpretation of the experimental micrographs. Throughout the whole range of reduction temperatures, images in both profile and planar views show the existence of a well-defined structural relationship between metal and support. The profile imaging technique has allowed us to study the rhodium/ceria interface. It consists of Rh (111) in epitaxial relationship with (111) ceria surface planes. For the whole metal particle two different crystallographic orientations with respect to the support, both compatible with a Rh (111)/CeO 2 (111) interface, were observed. Metal decoration phenomena have also been found. They could only be observed on catalysts reduced at either 973 or 1173 K, the covering effects being much heavier in the latter case. The metal particle size distributions corresponding to the reduced catalysts show that metal sintering is slight up to 973 K, with mean sizes ranging from 3.5 to 3.7 nm, and much stronger when the catalysts are reduced at 1173 K, mean size: 6.7 nm. Reoxidation studies at 373, 523, 773 and 1173 K, have revealed that upon O 2 treatment at 773 K the metal particles thoroughly transform into Rh 2 O 3 , the precise structural nature of which could not be unequivocally established. These studies have also shown that for oxygen treatments up to 773 K, metal redispersion is rather modest, being necessary to heat to 1173 K to induce the spread of the oxidized rhodium phase onto the support and the subsequent redispersion. For the catalyst reduced at 1173 K, the reoxidation at 773 K or below does not lead to the recovery of the metal decoration effects. The ensemble of results presented here are discussed in relation to the nature of the metal/support interaction phenomena occurring in Rh/CeO 2 catalysts. The influence of both the reduction and reoxidation treatments on the metal deactivation/regeneration of these catalysts is also discussed.

CO 2 adsorption on a series of La 2 O 3 /SiO 2 samples, with lanthana weight loadings ranging from 1.6% to 75%, have been studied. The results are interpreted on the grounds of a lantana—silica interaction model, also supported by data obtained from other physical characterization techniques (XRD, TEM, XPS). Such a model assumes that patches of an amorphous LaSiO phase, embedded into the silica matrix, modify the support surface in a progressive way, leading to a full coverage for 37.5% La 2 O 3 . The nature of the mixed phase imposes a top limit of 2.8 molecules nm −2 to its CO 2 adsorption capacity.

The interaction of CO at room temperature with a ceria supported rhodium catalyst was investigated using TPD-MS and a magnetic balance. The results have shown important differences in comparison with the H 2 Rh/CeO 2 system. In the presence of rhodium, the treatment with CO resulted in a much smaller degree of reduction of CeO 2 than with hydrogen. When, after CO adsorption at 294 K, the catalyst was heated at 773 K under vacuum, the reduction extent increased. In the case of hydrogen, the thermodesorption at 773 K almost completely reoxidized the ceria surface.

The influence of the preparation method on the microstructure and catalytic behavior of Rh and Ni dispersed on TiO2-SiO2 aerogels is investigated.

The high resolution transmission electron microscopy (HRTEM) study of Rh/CeO 2 and Rh/TiO 2 catalysts reduced at temperatures ranging from 473 K to 773 K suggests that the metal-support interaction phenomena they show are different. In contrast to that found for Rh/TiO 2 , over Rh/CeO 2 no metal decoration effects could be observed. Likewise, the chemisorptive and catalytic behaviour of Rh/ CeO 2 does not exhibit drastic changes with the reduction temperature. The HRTEM images, however, reveal the occurrence of quite singular rhodium-ceria interaction phenomena.

TiO2-SiO2 aerogels have been prepared by hydrolysis and polycondensation of alkoxides following two different methods: the classic one, using ethanol as a solvent, and the sonic one, by means of activation with ultrasound. The work is focused on the comparison of the textural properties of gels obtained by both synthetic routes. Nitrogen physisorption, mercury pycnometry and transmission electron microscopy have been used as characterization techniques. The sonogels present higher values of specific surfaces and apparent densities, lower pore volumes, finer and sharper pore-size distributions and lower average particle size. These properties are discussed and related to the preparation techniques.

This work reports on the preparation and characterization of a praseodymia sample to be used as a support for highly dispersed metals. The oxide sample was prepared by decomposing in a flow of helium, at 973 K, the phase obtained by precipitation with ammonia from a solution of Pr(NO3)3. The preparation conditions were established after investigating the thermal evolution of the precursor phase by thermogrammetric analysis, temperature-programmed decomposition-mass spectrometry, Fourier transform IR spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Data corresponding to the textural and chemical characterization studies carried out on the oxide are also presented and discussed.

This work reports on the preparation and characterization of a praseodymia sample to be used as a support for highly dispersed metals. The oxide sample was prepared by decomposing in a flow of helium, at 973 K, the phase obtained by precipitation with ammonia from a solution of Pr(NO3)3. The preparation conditions were established after investigating the thermal evolution of the precursor phase by thermogrammetric analysis, temperature-programmed decomposition-mass spectrometry, Fourier transform IR spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Data corresponding to the textural and chemical characterization studies carried out on the oxide are also presented and discussed.

TiO2 SiO2 aerogels have been used as supports to disperse rhodium. Three different ways have been followed for the preparations: (a) a classic TiO2 SiO2 aerogel, obtained from a mixture of alkoxides and water dissolved in ethanol, was impregnated with a rhodium nitrate solution; (b) a TiO2 SiO2 sonogel, obtained by hydrolysis of alkoxides in the absence of alcohol, under the action of ultrasound, was impregnated with a rhodium nitrate solution; and (c) a mixture of alkoxides and water, including rhodium nitrate in the reaction vessel, was exposed to the action of ultrasound, thus leading to a ternary Rh TiO2 SiO2 sonogel. The behaviour of these three catalysts has been compared with that of a Rh/TiO2 SiO2 system (d), obtained by conventional impregnation methods, starting from a commercial silica support. The samples prepared by impregnation of aerogels (a,b) present high levels of rhodium dispersion and show an increase of the catalytic activities in parallel with the pretreatment temperature in flow of hydrogen. On the contrary, the sample prepared including rhodium before gelling (c) presents a poor metallic dispersion, is not active for benzene hydrogenation, and has the capability of uptaking large amounts of hydrogen at ambient temperature. Both patterns of behaviour are greatly different from that characteristic of conventional Rh/TiO2 SiO2 catalyst (d).

High-resolution transmission electron microscopy has been applied to the characterization of the Rh/Sm2O3 system. The comparison between Rh/CeO2 and Rh/Sm2O3 catalysts suggests a model of behavior that would be operative for metals supported on rare-earth sesquioxides. The model assumes that a significant dissolution of the support takes place during the impregnation step. As a consequence, the metal would be present in a highly dispersed state after the drying process, forming a mixed phase with the support material, which explains why metal crystallites are only observed after reduction followed by heat treatment at high temperature.

The hydrogen chemisorption on two Rh/CeO 2 catalysts prepared respectively from rhodium nitrate and rhodium chloride has been studied. The evolution of the ceria oxidation state with the series of treatments applied was monitored by means of a magnetic balance. Temperature Programmed Reduction and Oxidation (TPR/TPO) as well as Volumetric Adsorption techniques have also been used. Upon treating with H 2 , at 623 K, the Precursor/Support systems, the reduction level reached by ceria was 11.4% for the sample prepared from Rh(NO 3 ) 3 and much higher, 22.1%, for the chlorine containing catalyst. In the later case, the reduction degree varied very slightly with succesive evacuation/hydrogen adsorption cycles. This contrasts with the behaviour observed for the sample prepared from rhodium nitrate, for which the reduction process is to a much larger extent reversible. The results reported here for RhCl 3 /CeO 2 are interpreted as due to the substitution of the ceria lattice oxygen ions by Cl − , thus blocking the operation of both the direct and incorporation of Cl − into the support. This induces a much higher irreversible reduction of ceria as well as the blocking of both the direct and back spillover processes responsible for the reversiblity of the ceria reduction by hydrogen.

A series of Rh/CeO2 catalysts reduced at temperatures ranging from 523 K to 1173 K has been investigated by O2 Pulses-TPO and HRTEM. Rhodium crystals can be fully oxidized to Rh2O3 by heating them at 773 K in flowing O2(5%)/He. The ceria oxidation state could also be determined in every case. Upon reduction at 1173 K, metal decoration and encapsulation phenomena do occur. This prevents the reoxidation of part of the rhodium crystals.

In the presence of rhodium, the H2–CeO2 interaction is to a large extent reversible, simple evacuation of the reduced sample has been demonstrated to promote reoxidation of the support; this explains some puzzling effects of the reduction/evacuation treatments on the actual oxidation state of ceria in Rh–CeO2 catalysts.

Metals supported on rare earth sesquioxides present a non- conventional behavior. Ordinary H2 and-or CO chemisorption techniques cannot be straightforwardly used to characterize this group of catalysts. The assessement to the data of metallic dispersions and the establishment of the occurrence and extent of metal-support interaction phenomena are determinant in order to interpret the properties of these catalysts in hydrogenation reactions. In this work HREM is proposed as a powerfull technique for the study of lanthana supported rhodium catalysts. Such catalysts would be considered as representative of a series of metals supported on rare earth sesquioxides.

This work reports on the chemical and microstructural characterization of a series of Rh/CeO 2 catalysts. The volumetric adsorption and FTIR spectroscopic studies show the occurrence of considerable changes in the chemistry of the H 2 -(Rh/CeO 2 ) system upon increasing the reduction temperature from 623 to 773 K. However, the H/Rh values determined from hydrogen isotherms at 191 K suggest that the rhodium microcrystals remain chemically active after reduction at 773 K. The major effect of the high-temperature reduction treatment would be the blocking of the spillover process, much slower on the catalysts reduced at 773 K. In agreement with this, no dramatic effect of the reduction temperature on the catalytic activity for benzene hydrogenation has been found

A series of Rh/TbO x catalysts reduced at temperatures ranging from 623–973 K has been studied by means of X-ray diffraction, thermogravimetric analysis, volumetric adsorption temperature programmed desorption/reduction mass spectrometer (catharometer) techniques. All the catalysts consists of Rh/Tb 2 O 3 . No strong metal-support interaction effect could be observed. The decrease of the H/Rh ratio with the reduction temperature is interpreted as due to metal sintering. The amount of H 2 chemisorbed by the support is not larger than 2 H atom nm 2 , thus suggesting a surface nature for this process.

In the framework of a research project aimed at developing alternative materials for application in three-way catalysis, this work reports on the preparation and characterization of a ceria-terbia mixed oxide supported on a lanthana-modified transition alumina. This complex multicomponent oxide system has been characterized by combining x-ray diffraction (XRD), high-resolution electron microscopy (HREM), temperature-programmed desorption mass spectrometry (TPD-MS), Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Following a dry impregnation procedure, the lanthana-containing phase was deposited first, the ceria-terbia oxide being dispersed on the modified alumina in a subsequent step. The structural and chemical characterization studies carried out on the La 2 O 3 /Al 2 O 3 binary system provide no evidence of a crystalline lanthana-containing phase. Neither lanthanum oxide nor the phases resulting from its aging in air could be identified. Likewise, no lanthana-alumina mixed oxide phases could be deduced from analysis of the HREM micrographs, selected-area electron diffraction (SAED) or XRD patterns. As deduced from the H 2 O and CO 2 TPD studies, the chemisorptive properties of the La 2 O 3 /Al 2 O 3 are significantly different from those of the alumina and the bulk lanthana. We conclude, accordingly, that the supported lanthana consists of a highly dispersed oxide in strong interaction with the alumina support. By contrast, after deposition and further calcination of the cerium-terbium nitrate precursors, the presence of fluorite microcrystals of average size 5 nm could be identified both by XRD and HREM. The XPS studies carried out on the alumina support, La 2 O 3 /Al 2 O 3 and CeTbO x /La 2 O 3 /Al 2 O 3 , as well as a series of reference systems consisting of aged-in-air lanthana, CeLaO x and CeTbO x mixed oxides, have revealed the presence in the ternary system (CeTbO x /La 2 O 3 /Al 2 O 3 ) of at least two different types of chemical environments for the lanthanum ions. With the help of the La 3d 5/2 spectra recorded for the different reference systems, we conclude that these two environments correspond to highly dispersed lanthana strongly interacting with OH- and/or CO 3 2- groups, and to La 3+ species incorporated in the Ce/Tb mixed oxide phase.

In the characterization of supported metal catalysts, it is important to understand the influence of the support on the metal particles since many catalytic properties are controlled by their interaction. Previous studies of supported Rh catalysts have shown that the oxide support plays an Important role in the activity and stability of the catalysts: the morphology and dispersion as well as the activity of the supported Rh particles can be affected significantly. High resolution electron microscopy (HREM), scanning transmission electron microscopy (STEM) and microdiffraction represent powerful techniques for studying the microstructure of supported small metal particles (In this study, the techniques of HREM and STEM/microdiffraction have been combined to characterize the structures of the Rh particles in Rh/CeO2 and their structural relationship with the cerium oxide support. The microscopes used were JEM-200CX, JEM-4000EX and VG HB-5 STEM. The following catalyst samples with various treatments have been studied