Adding value to natural clays as low‑cost adsorbents of methylene blue in polluted water through honeycomb monoliths manufacture

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

Clay honeycomb monoliths for the simultaneous retention of lead and cadmium in water

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. (c) 2022 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/)

Influence of gold nanoparticles size for photocatalytic NO oxidation in low loading Au/TiO2 catalysts

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) in Au/TiO2 photocatalysts for environmental remediation applications: Effectiveness enhancement and side effects

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

Ultrathin Washcoat and Very Low Loading Monolithic Catalyst with Outstanding Activity and Stability in Dry Reforming of Methane

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 degrees C, even under extreme Weight Hourly Space Velocities (WHSV 115-346 Lg(F -1)h(-1)), as well as in terms of stability during prolonged Time on Stream (TOS 24-48 h)

Copper-iron mixed oxide supported onto cordierite honeycomb as a heterogeneous catalyst in the Kharasch-Sosnovsky oxidation of cyclohexene

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. © 2021 The AuthorsThe authors thank the Ministry of Economy and Competitiveness of Spain (Projects MAT2017-85-719-R , and AGL2017-88083-R ), the Junta de Andalucía ( FQM-110 and FQM-169 groups), and the Institute of Electron Microscopy and Materials (IMEYMAT) of Cadiz University (UCA) (Projects HOMOGREEN and NUPRECAT) for their financial support. They also acknowledge the SC-ICYT of the UCA for using its XRD NMR, and electron microscopy division facilities

3D-printing of metallic honeycomb monoliths as a doorway to a new generation of catalytic devices: the Ni-based catalysts in methane dry reforming showcase

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

Acyloxylation of 1,4-Dioxanes and 1,4-Dithianes Catalyzed by a Copper−Iron Mixed Oxide

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