How important is the support during the rational design of a catalyst? Herein, doped ceria (Zr; Pr and Tb) was used as an active support to prepare Pt catalysts (0.5 wt%) for glycerol selective oxidation. A thorough characterization of achieved catalytic systems showed that the nature of doping elements led to different physicochemical properties. The presence of surface Pr3+ and Tb3+ not only increased oxygen vacancies but also electron mobility, modifying the oxidation state of platinum particles. The redox properties of the catalyst were also affected, achieving a close interaction between the support and metal particles even in the form of Pt-O-Pr(Tb) solid solutions. Furthermore, the combination of medium-sized metal particle dispersion, strong metal–support interaction and a synergy between the amount of oxygen vacancies and Pt0, observed in the Pt/CeTb catalyst, led to a high turnover frequency (TOF) and increased selectivity to glyceric acid. Thus, the present study reveals how a simple structural modification of active supports, such as cerium oxide, by means of doping elements is capable of improving the catalytic performance during glycerol selective oxidation, avoiding the cumbersome methods of synthesis and activation treatments.

A multidisciplinary approach has been followed for the development of structured catalysts based on 3D-printed metallic honeycomb monoliths, which allows overcoming some of the barriers that limit the industrial application of significant catalytic processes such as those related to CO2 valorization. In particular, nickel and/or cerium-containing catalysts have been incorporated into stainless steel honeycombs and evaluated in the Dry Reforming of Methane (DRM) reaction. Moreover, taking advantage of the conductive nature of the metallic substrate, a methodology that allows the incorporation of the active phase by electrochemical deposition has been implemented. The prepared catalysts were characterized by SEM coupled EDX compositional analysis, Xray fluorescence, X-ray diffraction, X-ray Photoelectron Spectroscopy and Temperature-Programmed Reduction. In contrast to the catalyst where cerium and nickel were co-deposited, the catalyst obtained by sequential electrodeposition of Ce (first) and Ni (second) proved to be highly active and stable in the DRM process, with conversions of both CH4 and CO2 above 90 % and H2/CO ratio of ca. 0.8 at 750 degrees C for more than 40 h. Moreover, the catalyst kept its good performance after doubling the flow proving its great potential for a real application at higher scale.

Air pollution, a major health concern, necessitates innovative solutions such as TiO2-based photocatalytic building materials to combat its harmful effects. This study focuses on developing high-performance TiO2 photocatalysts for NOx removal in building applications, aiming to overcome the limitations of commercial TiO2. These photocatalysts were synthesized via a hydrothermal method, with parameters such as synthesis time and post-treatment investigated to optimize their properties. Hydrothermal synthesis yielded TiO2 nanoparticles with reduced aggregation and a high proportion of elongated particles with exposed {010} facets. This resulted in significantly enhanced photocatalytic activity compared to commercial P25 in methylene blue degradation and NOx depollution. Subsequently, the optimized hydrothermal TiO2 was successfully integrated into a silica sol–gel coating for application on building materials. The coated concrete demonstrated significantly higher NOx removal efficiency and lower NO2 release, achieving a 1.7-fold improvement in overall NOx removal and significantly higher depolluting effectiveness compared to its P25 counterpart. These findings highlight the potential of hydrothermally synthesized TiO2 with controlled morphology for the development of high-performance, environmentally friendly building materials with enhanced air purification capabilities.

Rice husk, a byproduct of rice production, poses significant environmental challenges due to disposal issues, while the emission of volatile organic compounds into the atmosphere further exacerbates these concerns. This study addresses both problems by exploring the potential of texturally enhanced SiO2, derived from Uruguayan rice husk, as a catalytic support for manganese oxides in the combustion of volatile organic compounds. SiO2 was synthesized from rice husk ash using a sustainable, acid-free pretreatment method, yielding a notably high silica purity of 96.5%—a level comparable to or exceeding previously reported values, highlighting the high silica quality inherent in Uruguayan rice husk. The catalytic activity was evaluated using acetone as a model volatile organic compound, achieving up to 90% conversion with 30 wt.% manganese oxide at 300 °C, with CO2 as the primary product. Furthermore, a 24 h stability test demonstrated consistent performance, maintaining a conversion rate of around 95.6 ± 2.5%. These findings suggest that high-purity SiO2 derived from Uruguayan rice husk, with its sustainability benefits, offers an effective solution for acetone removal when supporting an active phase such as manganese oxides, addressing both rice husk disposal and volatile organic compound emissions.

Integral coal honeycomb monoliths were easily prepared achieving the cell densities typical of commercial cordierites through extrusion plus physical activation. Different techniques such as volumetric adsorption, TGA, TPD and transient kinetic analysis were employed to study their interaction with CO2 at different temperatures (35–100 °C) and under both static and dynamic atmosphere. The CO2 capture capacity resulted to be 0.95 mmol/g at 35 °C, much higher than that of previously studied clay honeycomb adsorbents. The CO2 uptake exhibited fast second order kinetics, and a wide operative window for a highly efficient CO2 removal was found. Moreover, due to a weak interaction, most CO2 adsorbed could be released at 110 °C, what allows minimizing the costs related to controlled regeneration if ones wants to reuse the captured CO2 but at the same time prevents from desorption when this is undesirable. Treatment of the coal honeycomb monolith with a 1:1 CO2+CH4-containing stream revealed, through gas chromatography analysis, the conversion into syngas at relatively low temperatures (50% at 750 °C) in spite of the metal-free character of the monolith. Moreover, this activity reached 90% and remained quite stable for at least 12 h at 900 °C. These results demonstrate the potential of preparing honeycomb monoliths from coal as a strategy to diversify the uses of this abundant natural resource and as an alternative in the field of CO2 capture and valorization.

This study assesses the efficacy of natural clays as a cost-effective and ecologically sound method for the removal of tetracycline from water. A notable advancement in the field of antibiotic removal is the utilization of honeycomb monoliths in lieu of traditional powder-based materials. The objective of this approach is to facilitate easier handling and to mitigate the production of sludge. The findings illustrate that, among the five clay types studied, the kerolitic montmorillonite is particularly effective in removing tetracycline from water, achieving levels of approximately 100 mg/g. This effectiveness is remarkably consistent across a range of pH levels (both acidic and basic), temperatures (4-60 degrees C), and even flow rates when employing the honeycomb design (50-2800 mL/min). These results substantiate the efficacy of this approach as a robust and promising strategy for wastewater treatment. In light of the fact that the principal mechanism of action for these clays is adsorption, the study also addresses ancillary concerns such as filter cleaning for reuse and the complete elimination of tetracycline.

Gold nanoparticles (AuNPs) supported on TiO2 are one of the most investigated photocat-alysts, however, the positive effect of AuNPs size reduction on Au/TiO2 activity is clear for conventional catalysis, but this relationship not strictly happens in photocatalysis. The present work investigates how small changes in the lower size range of AuNPs can affect the Au/TiO2 photoactivity in order to maximize the performance of photocatalysts with low metal loadings (<1 wt%). Precipitation-deposition methods and a speciation-controlled incipient wetness impregnation (ScIWI) method have been employed for preparing Au/TiO2 photocatalysts that exhibited a NOx elimination capacity significantly higher than pristine TiO2. Comparing the photocatalysts, ScIWI method achieved the highest gold dispersion and Au-TiO2 contact perimeter providing the most active photocatalysts, confirming the positive effect of AuNPs size reduction in the average sizes around 2 nm. In addition, on the basis of the results obtained, it has been proposed that the adsorption of nitrogen oxides species on gold has a relevant role on the NO photooxidation process.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Strong Metal−Support Interaction (SMSI) is a well-known phenomenon of heterogeneous catalysis that have not been extensively investigated in photocatalytic applications. Moreover, the reactions previously studied for photocatalysts under SMSI state are mainly restricted to energy related uses. The present work seeks to explore the effect of SMSI induced by soft wet-chemistry in a Au/TiO2 photocatalyst with specific focus on photocatalytic environmental remediation. With this aim, the developed photocatalyst has been evaluated considering liquid, gas and solid pollutants in order to represent the wide range of environmental photocatalysis applications. These photooxidation scenarios were methylene blue dissolved in water, gaseous NO, and soot directly deposited on the photocatalyst. The results revealed that the SMSI induction has a generally positive effect on photoactivity promoting the MB and soot removal by 53% and 60%, respectively. However, the SMSI did not provide any additional benefit in the NOx elimination compared to the non-SMSI Au/TiO2 photocatalyst, because the enveloping of AuNPs limits the gold-pollutant interaction.

A natural Moroccan illite-smectite clay was investigated as adsorbent of nickel in water. Before its use, it was processed without additives as honeycomb monoliths, an advantageous design in many methods developed to control environmental pollution. The performance of the resulting monoliths was studied in dynamic conditions by flow recirculation through the honeycombs and using Atomic Absorption Spectroscopy for the determination of residual nickel concentration in the solutions. Design of experiments (DoE) was employed to evaluate the influence of three parameters and their interaction on the nickel adsorption capacity of the clay honeycombs: nickel concentration (10-206 ppm), salt concentration (4-36 g/L), and water flow (94-364 mL/min). Based on previous studies, recirculation time, pH and temperature were fixed at 1 h, 4.5 and room temperature, respectively. The maximum amount of nickel adsorbed (0.83 mg/g of clay) was obtained for a nickel concentration of 206 ppm, a 218 mL/min flow, and a salt concentration of 4 g/L. Experimental conditions for the highest repeatability were estimated, the respective values being 108.2 ppm, 94 mL/min and 20 g/L. Nickel retention by the clay was also confirmed after the adsorption tests by direct characterization of the used structured adsorbent through X-ray Fluorescence and SEM-EDS.

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.

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.

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.

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.

Supported Ni catalysts (4.5 wt%) using a Ce-Zr oxide (18/82 molar ratio and a ceria-rich surface) depicting advanced redox properties, were deposited by washcoating over cordierite honeycombs (230 and 400 cpsi). FIB-STEM unveiled nanostructure details otherwise undistinguishable by conventional techniques. The catalytic performance was evaluated in the dry reforming of methane at 700-900 degrees C, using a CH4:CO2 1:1 feedstock, and exploring high Weight Hourly Space Velocity (115-346 L g(-1) h(-1)). The structured catalysts exhibited better performance than the corresponding powders, reaching values close to thermodynamic limits for both reactants conversion and H-2/CO ratio, from 750 degrees C, and no deactivation was observed in prolonged experiments (24-48 h). This was related to both the high catalyst efficiency after being deposited with low loading on the cordierite and the intrinsic advantages of the monolithic reactor, like preventing from the kinetic control that operates in powdered samples under high WHSV or limiting the deactivation.

Natural illite–smectite and stevensite Moroccan clays were used for the simultaneous removal of lead and cadmium from aqueous medium. The clays were employed in raw state and extruded as honeycomb monoliths form without any additives, which confirms the novelty of this approach in water treatment. The experiments were done in batch conditions with continuous stirring and using a recirculated flow, respectively. In addition to a characterization of the clays by XRF, XRD, TGA, laser granulometry, N2 physisorption, FTIR spectroscopy, SEM-EDS and evaluation of the cation exchange capacity, special attention was paid to the influence on the co-adsorption of variables such as adsorbent dosage, contact time and initial concentration of Cd2+ and Pb2+. Pseudo-second order kinetics and good fitting to Redlich–Peterson model for both heavy metals were found. Our results also suggest that Pb2+ and Cd2+ uptake is controlled by chemisorption with predominance of Langmuir characteristics. No significant depletion of the metals retention attributable to competition was observed, particularly for the stevensite (maximum retention capacity of 1.2 mg Pb2+/g and 4.6 mg Cd2+/g) that showed higher specific surface area. For both clays, cadmium ions adsorption was relatively favoured in the bimetallic solution, and the honeycombs kept the powders performance. Honeycomb monoliths as a compact adsorbent offer a promising way of water treatment thanks to their stability and easy incorporation into dynamic processes avoiding the issues of pressure drop under wastewater circulation.

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 H2-TPR, and tested in the dry reforming of methane reaction. In the 750–900 °C range, they showed competitive conversions (45–95%) and H2/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 °C due to their intrinsic nickel content.

A Ni/CeO2/ZrO2 catalyst with improved redox properties has been washcoated onto a honeycomb cordierite monolith in the form of a nonconventional alumina-catalyst layer, just a few nanometers thick. In spite of the very low active phase loading, the monolith depicts outstanding performance in dry reforming of methane, both in terms of activity, with values reaching the thermodynamic limit already at 750 °C, even under extreme Weight Hourly Space Velocities (WHSV 115–346 L·g−1·h−1), as well as in terms of stability during prolonged Time on Stream (TOS 24–48 h).

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.

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. (C) 2020 Elsevier Ltd. All rights reserved.

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 N-2 adsorption, XRD, XRF, SEM, XPS, H-2-TPR, O-2-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 degrees 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.