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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.

A copper-iron-based catalyst has been prepared by a low-temperature co-precipitation and sonication method. The use of high-energy ultrasound reduces the time required for the preparation process from one workweek to one day with respect to the catalysts obtained by conventional coprecipitation and thermal treatment methods. The resulting material has been characterized at compositional, textural, structural, and chemical levels by ICP-AES, BET, SEM-EDS, XRD, TEM, and FTIR among other techniques. The material shows catalytic activity in the acyloxylation reaction of 1,4-dioxane and cyclohexene under microwave irradiation. In parallel with the optimized catalyst synthesis, the use of microwaves allowed for a substantial improvement in the outcome of the reaction in terms of cleanliness, yield, and time.

Wild carob (WC), an abundant and unused lignocellulosic waste in Algeria, has been used as an inexpensive biosorbent for the elimination of methylene blue (MB) from the aqueous solution and as a precursor for the preparation of a new activated carbon by chemical activation with ZnCl2 (ACWC). The adsorbent materials were characterized by N2 physisorption, SEM/EDX, FTIR spectroscopy and isoelectric point (pHpzc) measurements. The adsorption performance of WC and ACWC was estimated for MB at different adsorption variables, such as solution pH (2–11), MB initial concentrations (25–200 mg L−1), time (0–1500 min), adsorbent dose (0.25–2.00 g L−1), temperature (10–40 °C) and NaCl concentration (0.0–0.5 M). The obtained results indicate that WC has an acidic surface due to the presence of carboxyl and phenol groups that play an important role in the fixation of cationic dye molecules, obtaining a maximum monolayer adsorption capacity of 84 mg g−1 at natural pH (7.5) and 40 °C. However, this adsorption performance was much higher in the case of the ACWC sample (218 mg g−1). From the equilibrium data, the Freundlich, Langmuir, Sips and Redlich–Peterson isotherms parameters of both samples were calculated and compared. For WC, the experimental data fitted well with Redlich–Peterson, Langmuir and Sips isotherm models, while in the case of ACWC they were best represented by the Redlich–Peterson and Sips isotherms. The adsorption kinetics data were found to follow the pseudo-second-order model for WC and the pseudo-first-order model for ACWC. The thermodynamic parameters suggest that, for both materials, the process was endothermic and spontaneous in the range of temperatures studied.

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.

Different natural Moroccan clays were used as adsorbents for the removal of lead from aqueous solution. The study was performed not only employing the starting clays in the form of powder but also after their extrusion as honeycomb monoliths, this representing the major novelty of this work respect to the current state-of-art. The experiments were done in batch conditions with continuous stirring and using a recirculated flow, respectively. In addition to an exhaustive characterization of the clays by means of X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, laser granulometry, N2 physisorption, infrared spectroscopy, SEM-EDS and evaluation of the cation exchange capacity, special attention was paid to the influence on the lead adsorption of variables such as adsorbent dosage, pH, contact time with the adsorbate and initial concentration of lead. Considering the cheap and abundant character of the raw materials, their easy processing (no additives were required for their extrusion) and the time and energy save due to no need for further modification through chemical/thermal activation, the obtained results (with retention over 90% for 30 ppm of lead) demonstrated the potential of the proposed design as low cost solution that may be competitive versus other technologies for water depollution, especially in developing regions.

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.

Clay honeycomb monoliths were manufactured from a natural montmorillonite and used for CO2 adsorption, their performance being compared with that of the same clay but in the form of powder. Volumetric adsorption isotherms, thermogravimetric studies, temperature-programmed desorption experiments and transient kinetic analysis, the two latter followed by mass spectrometry, were employed to investigate the interaction of the samples with CO2, both under static and dynamic conditions, and at different temperatures. This research demonstrated that the honeycomb monoliths kept the adsorptive properties of the starting material in terms of capture capacity (around 15 mg/g), Henry constant, heat of adsorption and activation energy. Most of retained CO2 was weakly adsorbed, the temperature needed for its release being 130 °C, an appropriate value which is sufficiently high to avoid undesirable desorption while being low enough to minimize the costs derived from controlled regeneration for further CO2 reuse. The kinetics of the CO2 uptake over the monolith (though of second order like over the powder) was slightly different, allowing a wider operative window for a highly efficient CO2 removal. These results suggest the potential of the honeycomb monolithic design for an even more competitive use of clays as low cost CO2 filters.

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.

An integrated process was investigated for the degradation of methylene blue (MB); it was based on the combination of adsorption and photocatalysis. A granular activated carbon (C) was considered for adsorption, which involved \(\hbox {TiO}_{2}\) as a photocatalyst (\(\hbox {TiO}_{2}/\hbox {C}\)). The \(\hbox {TiO}_{2}/\hbox {C}\) was directly obtained by an impregnation method using \(\hbox {TiCl}_{3}\); it was also calcined under air atmosphere at \(500\,{^{\circ }}\hbox {C}\) (\(\hbox {TiO}_{2}/\hbox {C}\)-500). These materials were characterized by TGA, BET, SEM, EDS mapping, SEM-EDS, and their \(\hbox {pH}_{\mathrm{{PZC}}}\) were measured. The results obtained showed that activated carbon (C) exhibited the best performances in terms of adsorption. The photocatalytic activity on the degradation of MB in aqueous solution under UV irradiation was tested and compared to that of \(\hbox {TiO}_{2}\) anatase (\(\hbox {TiO}_{2}\, \hbox {A}\)) and a mixture of carbon with \(\hbox {TiO}_{2 }\) (\(\hbox{C--TiO}_{2}\)). \(\hbox {TiO}_{2}/\hbox {C}\)-500 catalyst was found to be more active than the other catalysts; the C with high surface area provided sites for adsorption, allowing the migration of the dye to the surface of \(\hbox {TiO}_{2}\). A synergistic effect between C and \(\hbox {TiO}_{2}\) was shown, which enhanced the photocatalytic activity by retarding the recombination of photogenerated electron–hole pairs, improving light absorption.

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.

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

The high pollution levels in urban areas is producing a significant damage on buildings. The use of photoactive coatings on building materials can produce building surfaces with self-cleaning and de-pollutant properties. We have developed a simple sol-gel route for producing Au-TiO2/SiO2 photocatalysts which were applied on common cultural heritage stones. We studied the photoactivity efficiency of the photocatalysts under study against methylene blue, soot and NOx.

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.

Mn-Cu mixed oxides were deposited by ultrasonic impregnation on ceramic honeycomb monoliths. Its catalytic performance was evaluated in the combustion of ethanol and n-hexane, VOC molecules of different chemical nature. The catalysts were characterized by N2 physisorption, SEM-EDS, XRD, X-ray fluorescence, XPS, TPR, TPD-O2 and OSC measurements. It was observed that the catalyst with the lowest content of Mn-Cu phase was the most active in the combustion of ethanol. This was attributed to the higher content of Mn4+ and the increase of lattice oxygen mobility, which would favor a Mars-van Krevelen type mechanism. The catalyst with a medium content of Mn-Cu, proved to be the most active in the combustion of n-hexane. This was associated with a high content of oxygen vacancies and easy availability of oxygen adsorbed on the surface, promoting the combustion of n-hexane, possibly through a Rideal-Eley type mechanism. The catalyst with the highest content of the Mn-Cu phase showed low activity in combustion of ethanol and n-hexane, which was attributed to a higher crystallinity of the Mn-Cu phases generated. Fil: Morales, Maria Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentina Fil: Yeste, M. Pilar. Universidad de Cádiz; España Fil: Vidal, Hilario. Universidad de Cádiz; España Fil: Gatica, José M.. Universidad de Cádiz; España Fil: Cadus, Luis Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentina

Mn1−xCex (x = 0, 0.05, 0.1, 0.2 and 1) mixed oxide catalysts supported on cordierite monolith were prepared by ultrasonic impregnation and examined for the catalytic combustion of n-hexane. All catalysts were characterized in detail using N2 adsorption, XRD, XRF, SEM, XPS, H2-TPR, O2-TPD and OSC measurements. The Ce-Mn mixed catalysts and Mn catalyst, showed excellent catalytic activity. However, the addition of cerium to manganese catalyst did not increase its activity. The Mn-Ce mixed catalyst, with an intermediate content of Ce, presented the same activity as the Mn catalyst, but it proved to be more stable under extreme conditions of reaction, i.e. conditions of 100% conversion at 350 °C for a maximum of 34 h. Deactivation of Mn catalyst was associated with a transformation to unstable phases of manganese oxides, while the stability of the Mn-Ce mixed catalyst was attributed to the strong Mn-Ce interaction, which likely occurs through the formation of a small amount of solid solution. The synthesis method used allows generating in situ a monometallic catalyst as active as a bimetallic Mn-Ce catalyst under extreme reaction conditions; cheapening the cost of the catalytic system.

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.

TiO2 is a photocatalytic material that has proven to have the ability to produce self-cleaning and de-polluting building materials, which can be a valuable alternative to mitigate the pollution consequences. However, the TiO2 performance is limited in outdoor conditions due to its exclusive UV absorption. In this work, Au-TiO2 photocatalysts were integrated into a silica sol-gel synthesis in order to produce long-lasting coatings with self-cleaning and de-polluting properties on building materials. This simple synthesis allows the in situ application on buildings. The enhancement of TiO2 photoactivity by AuNPs was clearly demonstrated. The self-cleaning and de-polluting properties were evaluated using soot and NO, respectively, showing that AuNPs promote the TiO2 performance. In addition, the role of AuNPs size and their loading on TiO2 performance were investigated. It was demonstrated that the smallest AuNPs size (13 nm) and the intermedium gold content (0.5% w/w Au/TiO2) show the highest photoactivity.

The total oxidation of toluene was studied over a Co3O4/La-CeO2 catalyst in a Temporal Analysis of Products (TAP) set-up in the temperature range 713 K to 873 K in the presence and absence of dioxygen. It has been demonstrated that the reaction proceeds via a Mars-van Krevelen mechanism. The reaction rate increased 8.4 times if both toluene and dioxygen were present in the feed. The partial reaction order with respect to O2 diminished from 0.9 to 0.6 with an increase in temperature from 763 to 873 K. Adsorbed oxygen species with a lifetime of ∼8 s have been found on a catalyst fully oxidized by dioxygen. Catalysis of isotopically labeled (18)O2/(12)C6H5(13)CH3 results in the formation of products containing (18)O, which indicates that both lattice and adsorbed oxygen are involved in the total oxidation of toluene. The role of adsorbed oxygen is activation of the C-H bond in toluene. The reaction network of the catalytic total oxidation of toluene consists of the following sequence: adsorption of toluene on the catalyst surface; activation of toluene by dehydrogenation with adsorbed oxygen; oxidation of activated toluene mainly by the lattice oxygen and re-oxidation of the reduced catalyst by dioxygen.

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.

The allylic hydroxylation of enones using dioxygen as the oxidant has been studied. The reaction was first examined in the absence of any catalyst, using β-ionone as a model substrate. Then a new copper–aluminium mixed oxide, Cu–Al Ox, was prepared and characterized in order to be used as a catalyst. This oxide showed good activity, and provided the corresponding γ- or ϵ-hydroxylated enones, starting from different α,β- or α,β,γ,δ-unsaturated ketones. In all cases, the yields were significantly improved compared to experiments run in the absence of the catalyst. The reaction was selective, and the formation of epoxides or other overoxidation products was detected only to a minor extent. The described procedure is a technically straightforward synthetic alternative to those methods described to date involving many reaction steps or toxic reagents. The reactions were optimized using design of experiments techniques (DoE).

Texturally modified clay honeycomb monoliths were prepared for use as filters to remove pollutants from water solutions. An easy, economical, “green chemistry” activation route was employed during the preparation to enhance the adsorption capacity of the honeycombs. The method involves mixing the clay before its extrusion with a natural coal that is subsequently eliminated from the monolith by heating it under air at the lowest possible temperature (440 °C according to a thermogravimetric study). The size of the coal particles used as a template was intentionally modified by adjusting the milling process (dry or wet) and its duration (1–120 min) to modulate the porosity induced in the clay monoliths after their further burning. N 2 physisorption, mercury porosimetry, granulometry and SEM were used to investigate the influence of the above preparative variables on the textural properties of the clay, significant effects being found in the macropore range. Methylene blue adsorption tests under dynamic conditions suggest that there is a correlation between pollutant removal and the macropore structure generated. FTIR spectroscopy indicates that the differences observed in cationic dye adsorption over the monoliths must be related to their different texture rather than to differences in the nature of their surface hydroxyl groups.

A detailed structural and chemical characterization study has been performed, both at the micrometer and nanometer scale levels, throughout the different steps of preparation of a catalytic device consisting in Co3O4/La-modified-CeO2/Al2O3 powders washcoated onto a honeycomb-type cordierite monolith. High-resolution transmission electron microscopy (HREM) images obtained from the initial catalyst powder allowed us identifying the formation of 50–100 nm crystallites of a Co3O4 phase in contact with bundles of much smaller CeO2nanocrystallites. For the catalytic device, backscattered electron images and X-ray energy dispersive spectroscopy (XEDS) elemental maps acquired in a scanning electron microscope (SEM) provided quantitative estimate of key parameters of the washcoated monolith as the thickness of the catalyst coating and the percentage of the monolith internal surface covered by the active catalytic components. Electron transparent cross-section lamellae of the monolith coating were also prepared by ...

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.

Coal-based honeycomb monoliths extruded using methods developed for ceramic materials have been used to retain methylene blue and p-nitrophenol from aqueous solutions. The influence of the filters’ thermal treatment on their textural properties and performance as adsorbents was examined. Characterization by N2 physisorption, mercury porosimetry and scanning electron microscopy along with adsorption tests under dynamic conditions suggest that, depending on the pollutant and its initial concentration, it can be more convenient to previously submit the monoliths to a simple carbonization or to an additional activation, with or without preoxidation, as a consequence of their different resulting pore structures. Infrared spectroscopy indicates that their different adsorption behaviour seems not to be related to differences in their surface chemical groups. In addition, axial crushing tests show that the monoliths have an acceptable mechanical resistance for the application investigated.

Several recent publications report the use of low-cost and locally available adsorbents in biopurification systems to eliminate pesticides from water. Nonetheless, the literature is insufficient to cover this problem, and more investigations are needed in this field to evaluate the possible application of economical adsorbents to prevent pesticide water resources contamination caused by direct losses. This study focuses on the fate of endosulfan metabolites, in small-scale biopurification systems, using as adsorbents treated and untreated organic agricultural stones (date, olive and avocado). The effects of sorbent particle size, adsorbent dose, contact time, concentration of pesticide solution and temperature on the adsorption processes were systematically studied in batch experiments. Pesticide determination was carried out using stir bar sorptive extraction and gas chromatography coupled with mass spectroscopy. Maximum removal efficiency (94.8%) was reached for endosulfan sulfate (0.1 mg L(-1)) using the acid-treated date stones (ATOS) fraction

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.

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 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.

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).

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.

The regio- and stereoselective hydroxylation of α,β- or α,β,γ,δ- unsaturated ketones with air in the presence of KOtBu is investigated.