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A copper-iron mixed oxide was deposited by the washcoating procedure over cordierite honeycomb monoliths for its use as a heterogeneous catalyst in organic synthesis processes. In particular, the prepared catalyst, characterized by techniques such as X-ray fluorescence, X-ray diffraction, SEM-EDS, laser granulometry, adherence tests, Temperature-Programmed Oxidation and Temperature-Programmed Reduction, showed an excellent yield and stability in the selective production of the allylic ester derived from the Kharasch-Sosnovsky oxidation of cyclohexene with benzoic acid. The use of a structured catalyst here proposed opens up an interesting alternative to homogeneous catalysis in the field of synthetic chemistry.

The air pollution is becoming one of most important health problems around the world. Thus, the development of depolluting building materials is a crucial challenge. TiO2 is a photocatalyst with demonstrated performance for degradation of NOx and other typical pollutants. However, its limited absorption of solar light reduces its performance. In this study, Au-TiO2NPs are integrated into a silica matrix in order to produce long-lasting coatings with de-pollutant performance and applicability in building. The interaction between Au and TiO2 improves the photoactivity of TiO2 and it promotes a considerably increase in visible light absorption. A significant role of the AuNPs size and their loading on the material photoactivity has been also demonstrated. The lowest AuNPs size enhances the activity due to their better dispersion and subsequently, the higher Au-TiO2 interaction observed. Regarding the Au loading, the maximum photoactivity, in terms of NO conversion and dye degradation, was reached for the intermedium Au loading. It can be mainly associated to the abrupt increase of Au-TiO2 agglomeration for the highest loading evaluated. Finally, it has been stablished that AuNPs also increased the selectivity of the NO oxidation to nitrates and nitrites, reducing the amount of NO2 released.

Exhausted TWCs subjected to chemical/thermal treatments were used as a support of MnOx catalysts for the total combustion of acetone. The so-prepared new devices were characterized by using adherence tests, elemental and thermal analyses, XRD, N2 physisorption, and SEM-EDS. Incorporation of only 2.6 wt.% of the active phase (Mn2O3 and Mn3O4) to the recycled honeycomb considerably improved the catalytic response, achieving at 250 °C a 60% increase in acetone conversion with respect to the spent autocatalyst. The following procedure is proposed as a simple way to provide the TWC devoid of noble metals a second life in the VOCs’ oxidation field.

Single-phase oxygen stoichiometric LaMnO3 and doped La0.8A0.2MnO3 (A = Ca, Sr, Ba) perovskites have been prepared by a simple one-step auto-combustion method. Cation-deficient LaMnO3+δ and La0.8A0.2MnO3+δ were obtained by calcination of the former samples in air at 750 °C. The samples were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed oxygen desorption, and N2 physisorption in order to apply them as catalysts in the complete catalytic oxidation of acetone as a model volatile organic compound. The studied phases show the expected orthorhombic and rhombohedral perovskite crystal structures. Catalytic experiments performed with all the samples show measurable activity already at 100 °C. At 200 °C, doped La0.8A0.2MnO3 samples show higher activity than undoped LaMnO3, with increasing conversion with larger A-cation size. Calcined samples also show higher activity than as-prepared ones making La0.8Ba0.2MnO3+δ the best catalyst at this temperature. All doped samples show >95% acetone conversion at T ≥ 250 °C with a weak dependence on the sample processing or A cation doping. The collected evidence confirms that the most important factors for the catalytic activity of these oxides are the Mn4+/Mn3+ molar ratio on the surface of the samples and the cation-deficiency of the bulk perovskite structure. In addition, increasing the symmetry of the bulk crystal structure appears to have an additional favourable effect. Despite the observation of the presence of surface carbonates, we show that it is possible to use the as-prepared samples without further thermal treatment with good results in the oxidation of acetone.

Stainless-steel honeycomb monoliths (square cell-shape/230 cpsi cylinders) were 3D-printed and used as support of a Ni/CeO2-ZrO2 powder deposited by washcoating. The resulting catalysts were characterized by XRF, SEM-EDX and H-2-TPR, and tested in the dry reforming of methane reaction. In the 750-900 degrees C range, they showed competitive conversions (45-95%) and H-2/CO ratio (0.84-0.94) compared to cordierite honeycombs with same catalyst loading and geometric characteristics, but did not require activation time thanks to better heat transfer. Both structured catalysts were stable in prolonged TOS experiments. The bare metallic monoliths exhibited significant activity at 900 degrees C due to their intrinsic nickel content.

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.

natural Moroccan illite–smectite was used as an adsorbent for the removal of methylene blue (MB) from aqueous solutions. The clay was characterized by FTIR spectroscopy, TGA, SEM–EDS, X-ray fluorescence, XRD and N2 physisorption. The influence of pH, temperature and time on the MB adsorption by the clay was investigated. The maximum equilibrium adsorption capacity was 100 mg g−1 at 45 °C. The kinetic behavior and the isotherms better-fitted with the pseudosecond- order and Langmuir models, respectively. Clay honeycomb monoliths (50 cells cm−2) were obtained by means of extrusion from the starting material without any additive except water. The structured filters exhibited better performance under dynamic conditions than the powdered clay, adding value to the application of this low-cost adsorbent.

Two natural Moroccan clays, an illite-smectite (O) and a stevensite (ST), were used to manufacture honeycomb monoliths for the removal of cadmium from aqueous solution. This goal was based on their easy extrudibility without additives and good performance for organic dyes and lead removal in previous studies. First, the influence of adsorbent dosage, time, pH and initial Cd(II) concentration was studied through batch experiments with the clay powders. Then, flow recirculation tests with the clays conformed as structured filters were performed. These confirmed the kinetics and adsorptive model, pseudo-second order and Langmuir, respectively, no matter the linear or non-linear character of the regression followed to fit the experimental data. With both experimental and sample designs, ST exhibited better performance than O. This could not be attributed to an exchange with Mg(II) overlapping the adsorption, despite its greater content in this element. Clay honeycombs behaved also better than packed columns charged with the same amount of powdered clay in similar experiments. Their maximum adsorption capacity (4 mg/g) ensures complete depuration of a solution containing 150 ppm of Cd(II) after recirculation through a 10 cm long and 3 cm-diameter monolith with the help of a centrifugal pump for less than 10 h.

Made available in DSpace on 2020-12-10T17:37:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-08-01 Spanish Government (Ministerio de Economia y Competitividad) Junta de Andalucia Bioleaching studies were carried out on a commercial nickel-based reforming catalyst using two acidophilic bacteria (Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans) under several types of bioleaching mode (one-step, two-step and spent medium-step) and catalyst pretreatment (with and without reduction). The highest percentage of nickel extraction was achieved using A. thiooxidans under spent medium-step (94.4 +/- 0.1%). The percentage of nickel extracted was constant (85.6 +/- 3.9%) up to a pulp density of 5% w v(-1), and it decreased at higher pulp densities due to acid depletion. In order to assess the potential reuse of the recovered metal, the nickel solution obtained by bioleaching was recycled by using it to prepare a new Ni/Al2O3 catalyst by impregnation of a commercial alumina support. Characterization of the catalyst prepared from recycled nickel showed that it had a high purity along with a suitable texture and metallic dispersion. Indeed, the activity of the new catalyst in the dry reforming of methane provided a high conversion of methane (99%) with good stability over time under the experimental conditions employed. Sao Paulo State Univ, Inst Chem, UNESP, BR-14800900 Araraquara, SP, Brazil Univ Cadiz, Dept Mat Sci Met Engn & Inorgan Chem, Cadiz 11510, Spain Univ Cadiz, Inst Electron Microscopy & Mat IMEYMAT, Fac Sci, Cadiz 11510, Spain Univ Cadiz, Inst Univ Invest Vitivinicola & Agroalimentario I, Fac Sci, Dept Chem Engn & Food Technol, Cadiz 11510, Spain Sao Paulo State Univ, Inst Chem, UNESP, BR-14800900 Araraquara, SP, Brazil Spanish Government (Ministerio de Economia y Competitividad): CTM2016-79089-R Spanish Government (Ministerio de Economia y Competitividad): MAT2017-87579-R Junta de Andalucia: TEP-105 Junta de Andalucia: FQM-110

Co 3 O 4 /La-modified-CeO 2 /Al 2 O 3 powders washcoated onto ceramic and metallic monolithic catalysts have been compared in order to evaluate the contribution of both the type of substrate and the total washcoat loading on the actual surface structure of the corresponding monolithic devices. Detailed structural and chemical characterization studies have been performed combining FIB (Focused Ion Beam) and STEM (Scanning Transmission Electron Microscopy). Atomic scale STEM data recorded on the electron-transparent lamellae prepared by FIB were complemented with those coming from micron scale analysis performed by different SEM (Scanning Electron Microscopy) techniques combined with digital image analysis. X-Ray Energy Dispersive Spectroscopy (X-EDS) elemental maps, acquired from the FIB lamellae, revealed the occurrence of an unexpected surface structure with large ceria aggregates constituted by crystallites with an average size 5 nm and Co 3 O 4 nanocrystallites with two layered structure underneath of some of these aggregates. The existence of this particular structure has been observed for all the samples analyzed here, and seems to be independent of either the nature of the support (ceramic or metallic) and/or the total amount of deposited material. All the investigated monolithic catalysts show high activity and selectivity to total oxidation of model VOCs (Volatile Organic Compounds) such as toluene and ethyl acetate. The present study highlights the key role of the combination of the FIB sample preparation and STEM to monitor the influence of the preparation method on the actual surface of catalytic monolithic devices, confirming the occurrence of microstructural features driven by physical processes involved in the multistep procedure of the washcoating technique followed to prepare the final monolithic device.

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.

The use of a copper−iron mixed oxide as a heterogeneous catalyst for the efficient synthesis of α-acyloxy-1,4-dioxanes and 1,4-dithianes employing t-butyl peroxyesters is reported. The preparation and characterization of the catalyst are described. The effect of the heteroatoms and a plausible mechanism are discussed. The method is operationally simple and involves low-cost starting materials affording products in good to excellent yields.

Two factors are key in the design of a TiO2 photocatalyst for building materials that meets the requirements for environmental applications: the TiO2 light absorption restricted to UV and its poor adhesion to the substrates. In this work, two strategies of TiO2 modification, nitrogen doping and AuNPs deposition, were combined in order to promote the TiO2 photoactivity under solar radiation. By the other hand, the Au/N–TiO2 photocatalysts were incorporated in a silica sol allowing their application by spray on three different building material substrates (limestone, granite and concrete), where the sol spontaneously produced Au/N–TiO2/SiO2 well-adhered coatings. The samples photoactivity was evaluated by dye degradation tests and NO abatement measurements. The obtained results demonstrated that the AuNPs considerably enhanced the photoactivity of N–TiO2, doubling the amount of NOx removed under UV–visible light. In addition, the role of the substrate and the TiO2/SiO2 ratio of the coating were also investigated. The coatings practically triplicated their depolluting effectiveness on concrete in comparison with their application on limestone. A direct correlation between the TiO2 loading and the photoactivity was observed, increasing NOx abatement by a factor of 1.3 when the Au/N–TiO2 loading of the coating was raised from 10 to 25%. However, the Au presence can induce evident colour modifications of the treated substrates that can limit the product application on certain substrates.

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.

As is well known, carbonaceous materials are good catalysts for methane decomposition, a promising alternative to methane reforming and water gas shift reactions, as the CO2-free production of hydrogen can be attained. Nevertheless, the continued absence of literature on the use of carbon-based honeycomb monoliths for this application is surprising, despite the monolithic honeycomb design offering obvious advantages compared with conventional packed beds. Therefore, in this work we have prepared integral carbon monoliths and tested them in catalytic CH4 decomposition. The reaction has been studied at different temperatures (750–900 °C) and the deactivation with time has been also monitored. Special attention was paid to the influence of the texture generated by different thermal treatments to which the monoliths are subjected after their preparation to eliminate the additives and activate the carbon. For this purpose a deep textural characterization has been carried out. Comparison with the same samples but in the form of powders was also performed.

In this paper a Ru/Ce0.8Tb0.2O2−x/Al2O3 catalyst has been prepared by incipient wetness impregnation method and it has been exhaustively characterized through N2 physisorption, H2 and CO chemisorption, temperature programmed desorption, infrared spectroscopy, X-ray diffraction and electron microscopy techniques. The catalyst has been tested in the water gas shift reaction and it has been compared with Ru/Al2O3 and Ru/Ce0.8Tb0.2O2−x samples employed as references. This study has revealed that WGS occurs with simultaneous methanation in the ceria–terbia containing systems. Catalytic tests performed in consecutive cycles reveal that the ternary system exhibit higher stability under ageing reaction conditions. These results appear as promising for deep abatement of CO in highly-pure H2 production from hydrocarbon reforming processes.

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.

Integral 90 wt% carbon-honeycomb lab-scale monoliths prepared from coal are characterized and applied to adsorb o-xylene. Textural characterization shows that the monoliths obtained after activation of the carbon exhibit appropriate porosity for their use as adsorbents. Their total capacity to retain o-xylene proves to be similar to that previously reported for studies under dynamic conditions on activated carbons but in the form of powder. To cite this article: J.M. Gatica et al., C. R. Chimie 9 (2006).

By combining FTIR spectroscopy of chemisorbed CO and HRTEM, we have studied the evolution undergone by the metal chemisorption capability and nanostructural properties of a Pt/CeO2 catalyst reduced at increasing temperatures from 200 to 500°C. As revealed by the νCO integrated absorption data on Pt, a progressive metal deactivation is observed. The analysis of the HRTEM micrographs allows us to exclude metal sintering, decoration, and Pt–Ce alloying phenomena as the likely origin of the observed effect. If the catalyst reduced at 500°C is further heated under CO2 (300 Torr), at a very mild temperature, 200°C, its chemisorption capability is partly recovered. This regeneration effect is interpreted as due to the Pt-assisted CO2 re-oxidation of the ceria support with inherent chemisorption of the resulting CO on the metal microcrystals. These observations are consistent with the model recently proposed by our laboratory on the nature of the strong metal–support interaction phenomena occurring in NM/CeO2 catalysts.

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.

The objective of this study was to examine the mechanism of the reduction by hydrogen of ceria−zirconia (CZ) mixed oxides having a high BET surface area (100 m2 g-1). Three methods were used in parallel to assess the Ce3+ content, the surface and bulk oxygen vacancy concentrations, and the resulting oxygen storage capacity (OSC): temperature programmed reduction, Fourier transform infrared (FT-IR) measurements of methanol adsorbed on the reduced surfaces, and a Faraday microbalance to determine the magnetic susceptibility of the reduced oxides. The three methods conclude that the introduction of zirconium into the ceria lattice has a positive influence on the OSC. Compared to pure ceria, the CZ mixed oxides exhibit better redox properties, with a lower temperature of initial reduction and a higher reduction percentage for all compositions. The reducibility increases with the zirconium content, however the OSC per gram of solid is practically the same for Zr contents between 20% and 50%. The reduction pro...

High surface area CeO2–ZrO2 mixed oxides were treated at 900–950°C either under wet air or under successive reducing and oxidizing atmospheres in order to study the evolution of the oxygen storage capacity (OSC) of these solids after different aging treatments. Several complementary methods were used to characterize the redox behavior: temperature programmed reduction (TPR) by H2, TPO, magnetic susceptibility measurements to obtain the Ce3+ content, FT-IR spectroscopy of adsorbed methanol and a method to compare the oxygen buffering capacity (OBC) of the oxides. All the results confirm that the mixed oxides exhibit better redox properties than pure ceria, particularly after aging. The enhancement in the OSC at moderate temperature has to be related to a deeper penetration of the reduction process from the surface into the under-layers. Redox cycling aging promotes the reduction at low temperature of all the mixed oxides, the improvement being much more important for low surface area aged samples. The magnitude of this effect does not depend on the BET surface areas which have similar values after cycling. This underlines the critical influence that the preparation and activation procedure have on the final OSC behaviors of the ceria–zirconia mixed oxides.

Les impuretes superficielles contenues dans une serie d'oxydes mixtes cerine-zircone ont ete etudiees par TPO/TPD et spectroscopie infrarouge. Les impuretes provenant soit des precurseurs soit de la contamination atmospherique (carbonates) ont ete identifiees et leur stabilite thermique a ete etudiee en fonction de differents traitements thermiques. Une methode thermique de purification est proposee afin d'obtenir des poudres de qualite suffisante pour les applications catalytiques.

In this work, the influence of the preparation procedure on the chemical and microstructural properties of a series of Rh/La 2 O 3 /SiO 2 catalysts has been investigated. The catalysts were characterized by using HREM, H 2 and CO volumetric adsorption and FTIR spectroscopy of chemisorbed CO. From our study, significant effects were observed for the following preparative variables: (a) the lanthana loading; (b) the way of introducing the metal and promoter, either consecutive (lanthana first and then the rhodium salt) or by co-impregnation; and (c) the calcination temperature (873 K or 1173 K) applied for preparing the La 2 O 3 /SiO 2 intermediate phase onto which the noble metal was deposited.

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

International audience; TPR, TPO, O2 pulses and magnetic balance experiments have been performed to study the effect of two different aging treatments, in oxidizing atmosphere and in reducing conditions, on the redox behavior of a Ce0.68Zr0.32O2 mixed oxide. It has been observed that, although the samples resulting from both treatments have similar textural properties, their redox behavior is significantly different. In particular, aging in H2 improves the oxygen storage capacity (OSC) at low temperatures by decreasing the temperature at which reduction takes place. Also, the oxygen buffering capacity (OBC) is enhanced after aging under reducing conditions. In addition, the study of the re-oxidation of the samples reveals that the rate of the O2 uptake increases if compared with the fresh sample or that aged in air. High resolution electron microscopy and Raman spectroscopy data have also been used to obtain information on the possible origin of such effects.