Nanostructured ceria-based catalysts for automotive application - Formulation of nanostructured systems for diesel and gasoline-type engines

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Natural Zeolite Clinoptilolite Application in Wastewater Treatment: Methylene Blue, Zinc and Cadmium Abatement Tests and Kinetic Studies

In recent decades, several abatement techniques have been proposed for organic dyes and metal cations. In this scenario, adsorption is the most known and studied. Clinoptilolite was considered, since it is a zeolite with a relatively low cost (200-600 $ tons-1) compared to the most well-known adsorbent used in wastewater treatment. In this work, Clinoptilolite was used for the adsorption of Methylene Blue (MB) at three different concentrations, namely, 100, 200, and 250 ppm. Furthermore, the adsorption capacity of the natural zeolite was compared with that of Activated Charcoal (250 ppm of MB). The two adsorbents were characterized by complementary techniques, such as N2 physisorption at -196 °C, X-ray diffraction, and field emission scanning electron microscopy. During the adsorption tests, Clinoptilolite exhibited the best adsorption capacities at 100 ppm: the abatement reached 98% (t = 15 min). Both Clinoptilolite and Activated Charcoal, at 250 ppm, exhibited the same adsorption capacities, namely, 96%. Finally, at 250 ppm MB, the adsorption capacity of Clinoptilolite was analyzed with the copresence of Zn2+ and Cd2+ (10 ppm), and the adsorption capacities were compared with those of Activated Charcoal. The results showed that both adsorbents achieved 100% MB abatement (t = 40 min). However, cation adsorption reached a plateau after 120 min (Zn2+ = 86% and 57%; Cd2+ = 53% and 50%, for Activated Charcoal and Clinoptilolite, respectively) due to the preferential adsorption of MB molecules. Furthermore, kinetic studies were performed to fully investigate the adsorption mechanism. It was evidenced that the pseudo-second-order kinetic model is effective in describing the adsorption mechanism of both adsorbents, highlighting the chemical interaction between the adsorbent and adsorbate

Correction to: Cerium–Copper–Manganese Oxides Synthesized via Solution Combustion Synthesis (SCS) for Total Oxidation of VOCs

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Cerium–Copper–Manganese Oxides Synthesized via Solution Combustion Synthesis (SCS) for Total Oxidation of VOCs

Abstract A set of cerium–manganese–copper oxide catalysts with various foreign metal contents was prepared via the solution combustion synthesis (SCS). The catalysts were characterized by complementary techniques such as N2 physisorption at − 196 °C, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), H2-temperature-programmed reduction (H2-TPR), O2-temperature-programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). Their catalytic activity was tested towards the VOC oxidation using ethylene and propylene as probe molecules. As a whole, it has been observed that the Ce55Mn45 sample (Mn 45 at.%), containing MnOx clusters interacting with the ceria phase, was the most active catalyst for propylene oxidation, exhibiting a complete conversion at 250 °C. On the other hand, the ternary oxide catalyst (Ce55Mn22.5Cu22.5 with Mn = 22.5 at.% and Cu = 22.5 at.%) has exhibited the best results for the oxidation of ethylene. These findings suggest that the co-presence of different active phases on the catalytic surface may have a beneficial (multiplicative) role on the whole reactivity. Finally, the most active powder catalysts were wash-coated in a SiC monolith and tested in a bench-scale reactor. As a whole, the catalyzed monoliths performed the complete oxidation of either ethylene or propylene at lower temperatures (550 and 450 °C, respectively) than those required to thermally decompose these molecules. Graphic Abstrac

Modification and characterization of clinoptilolite for the co-immobilization of formate dehydrogenase and glycerol dehydrogenase enzymes

In the last decades there is a rising concern for the increasing concentration of carbon dioxide, considered the major responsible of Global Warming. A solution to this critical issue is the catalytic conversion of CO2 into high value-added products. Among the different strategies that could be applied, the enzymatic process of CO2 reduction to methanol, employing a sequence of three enzyme-catalyzed reactions, seems to be very promising. The simultaneous employment of formate dehydrogenase and glycerol dehydrogenase allows to reduce CO2 to formic acid, the first of the sequential reactions, and at the same time regenerate the nicotinamide cofactor, that is very expensive. To reuse enzymes, with a consequential reduction of cost, and increased their stability, they can be immobilized on a proper support. In this context, porous materials, such as zeolites, present appropriate features to be suitable for enzymes immobilization. In particular, they are well suited for the covalent immobilization technique due to the fact that they can be functionalized with different functional groups. Natural zeolites, like Clinoptilolite have the advantage to be low-cost materials largely diffused in different part of the world. Clinoptilolite was subjected to dealumination-desilication treatments to modify the zeolite’s morphology, increasing its specific surface area. According to the literature, the dealumination procedure was done with sequential acid attacks using HCl solutions. Instead, for the subsequent desilication process NaOH solution is required. The effects of desilication-dealumination treatments were investigated through complementary techniques such as N2 physisorption at -196 °C, XRD and SEM. The analysis revealed that the Clinoptilolite specific surface area increased by 400% following the dealumination-desilication procedure; at the same time the XRD analysis shows that the processed Clinoptilolite has the same main peaks of the unmodified one. Finally, the retained activity and the stability of the immobilized enzymes were evaluated, the results show that these aspects were enhanced by the modification through acid-alkaline attacks of the Clinoptilolite

Simultaneous CO2 reduction and NADH regeneration using formate and glycerol dehydrogenase enzymes co-immobilized on modified natural zeolite

In this work, the co-immobilization of formate dehydrogenase (FDH) and glycerol dehydrogenase (GlyDH) enzymes is proposed to reduce CO(2) into formic acid, an important chemical intermediate. The reduction of carbon dioxide is carried out by FDH to obtain formic acid, simultaneously, the GlyDH regenerated the nicotinamide cofactor in the reduced form (NADH) by the oxidation of glycerol into dihydroxyacetone. Natural zeolite was selected as immobilization support given its good properties and low cost. The natural zeolite was modified with subsequent acid-alkaline attacks to obtain a mesostructurization of the clinoptilolite. The two enzymes were co-immobilized on clinoptilolite, previously hetero-functionalized with amino and glyoxyl groups. The distribution of the enzymes was confirmed by fluorescence microscopy analysis. Furthermore, a great increase in the retained activity for the formate dehydrogenase enzyme was noted, passing from 18% to 89%, when the mesostructured clinoptilolite was used as support. The immobilization yield of formate dehydrogenase and glycerol dehydrogenase is around 100% with all the supports studied. The promising results suggest a possible development of this procedure in enzyme immobilization and biocatalysis. The biocatalysts were characterized to find the optimal pH and temperature. Furthermore, a thermal stability test at 50 °C was carried out on both enzymes, in free and immobilized forms. Finally, it was shown that the biocatalyst is effective in reducing CO(2), both by using the cofactor in the reduced form (NADH) or the oxidized form (NAD(+)), obtaining NADH through the regeneration with glycerol in this latter case

CO Oxidation Over Ceria-Based Catalysts: Comparison of Single and Binary Metal Oxides

Wet air oxidation (WAO) of lignocellulosic biomasses is a promising route for the production of renewable and valuable compounds. In this work, acetovanillone (AV) was selected as lignin model molecule in order to investigate its behavior under the WAO reaction conditions. The experiments were carried out in a pressurized 50 ml batch reactor loaded with NaOH 2M as solvent, the reaction takes 1 h with temperatures ranging from 130 to 190 °C and air pressures between 5 and 30 bar. The perovskite-type mixed oxide LaFeO3 was synthetized and used as heterogeneous catalyst in order to improve the activation of molecular oxygen. Vanillin yield resulted to benefit from high reaction temperature showing a maximum carbon yield of 22%, instead the formation of carboxylic acids from the oxidative degradation of AV largely benefits from high pressure of air, exhibiting an overall carbon yield of 35%. The produced compounds include oxalic, glycolic, lactic, malonic, and levulinic acid

Natural Zeolite Clinoptilolite Application in Wastewater Treatment: Methylene Blue, Zinc and Cadmium Abatement Tests and Kinetic Studies

In recent decades, several abatement techniques have been proposed for organic dyes and metal cations. In this scenario, adsorption is the most known and studied. Clinoptilolite was considered, since it is a zeolite with a relatively low cost (200–600 $ tons−1) compared to the most well-known adsorbent used in wastewater treatment. In this work, Clinoptilolite was used for the adsorption of Methylene Blue (MB) at three different concentrations, namely, 100, 200, and 250 ppm. Furthermore, the adsorption capacity of the natural zeolite was compared with that of Activated Charcoal (250 ppm of MB). The two adsorbents were characterized by complementary techniques, such as N2 physisorption at −196 °C, X-ray diffraction, and field emission scanning electron microscopy. During the adsorption tests, Clinoptilolite exhibited the best adsorption capacities at 100 ppm: the abatement reached 98% (t = 15 min). Both Clinoptilolite and Activated Charcoal, at 250 ppm, exhibited the same adsorption capacities, namely, 96%. Finally, at 250 ppm MB, the adsorption capacity of Clinoptilolite was analyzed with the copresence of Zn2+ and Cd2+ (10 ppm), and the adsorption capacities were compared with those of Activated Charcoal. The results showed that both adsorbents achieved 100% MB abatement (t = 40 min). However, cation adsorption reached a plateau after 120 min (Zn2+ = 86% and 57%; Cd2+ = 53% and 50%, for Activated Charcoal and Clinoptilolite, respectively) due to the preferential adsorption of MB molecules. Furthermore, kinetic studies were performed to fully investigate the adsorption mechanism. It was evidenced that the pseudo-second-order kinetic model is effective in describing the adsorption mechanism of both adsorbents, highlighting the chemical interaction between the adsorbent and adsorbate

Immobilization of LDH enzyme on mesoporous silica with FDH as a cofactor regeneration system for the evaluation of novel cancer drugs

Tumor cells are characterized by the uncontrolled growth and the production of high amount of lactic acid via the Cori cycle (anaerobic conditions). The production of lactic acid is catalyzed by the A form of Lactate dehydrogenase (LDH A). Thus, the immobilization of LDH has shown to serve as a simple method to study the inhibition by means of anticancer inhibitors. In our previous work, we successfully immobilized the Formate dehydrogenase (FDH) on synthesized mesoporous silica, Mesoporous Cellular Foams-type (MCF). In this scenario, the similarities between the protein structure of FDH and LDH allows predicting a good performance of MCF as support for LDH enzyme