Search

In this work, four cobalt-based catalysts were obtained using two routes of preparation which differed in the expected degree of interaction with the silica matrix, using salicylic acid as a sacrificial modifier during the synthesis to modulate the interaction between the cobalt phase and the silica support due to its complexing properties. The catalysts were tested for the hydroconversion of guaiacol at 300 °C and 5 MPa of H2, with clear differences between each procedure. It is found that the synthesis route has a deep impact on the catalytic activity, with the catalysts prepared using a one-pot route being less active and having an increased selectivity to cyclohexane. In contrast, the ones prepared using a two-step process have increased yield towards phenol and cyclohexanol under the conditions used herein. Salicylic acid increases the catalytic activity in comparison to the untreated material for both families of materials, without changing the observed selectivity between samples with the same preparation. [ABSTRACT FROM AUTHOR]

The photocatalytic conversion in aqueous media of phenol and guaiacol as a lignin model compound using Nb2O5 with different crystal phases was studied. Nb2O5 particles were synthesized using hydrothermal methods, where it was observed that changes in the solvent control their morphology and crystal phase. Different photocatalytic behavior of Nb2O5 was observed with the selected model compounds, indicating that its selection directly impacts the resulting conversion and selectivity rates as well as the reaction pathway, highlighting the relevance of model molecule selection. Photocatalytic conversion of phenol showed conversion rate (C%) up to 25 % after 2 h irradiation and high selectivity (S%) to pyrogallol (up to 50 %). Orthorhombic Nb2O5 spheres favored conversion through free hydroxyl radicals while monoclinic rods did not convert phenol. Guaiacol photocatalytic oxidation showed high conversion rate but lower selectivity. Orthorhombic and monoclinic Nb2O5 favored the formation of resorcinol with S % ~0.43 % (C % ~33 %) and ~13 % (C % ~27 %) respectively. The mixture of both phases enhanced the guaiacol conversion rate to ~55 % with ~17 % of selectivity to salicylaldehyde. The use of radical scavengers provided information to elucidate the reaction pathway for these model compounds, showing that different reaction pathways may be obtained for the same photocatalyst if the model compound is changed. [ABSTRACT FROM AUTHOR]

The increasing CO2 emissions and their direct impact on climate change due to the greenhouse effect are environmental issues that must be solved as soon as possible. Metal–organic frameworks (MOFs) are one class of crystalline adsorbent materials that are thought to have enormous potential in CO2 capture applications. In this research, the effect of changing the metal center between Zr(IV), Ce(IV), and Hf(IV), and the linker between BDC and PDC has been fully studied. Thus, the six UiO-66 isoreticular derivatives have been synthesized and characterized by FTIR, PXRD, TGA, and N2 adsorption. We also report the BET surface area, CO2 adsorption capacities, kinetics, and the adsorption isosteric heat (Qst) of the UiO-66 derivatives mentioned family. The CO2 adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, Avrami's kinetic models, and the rate-limiting step with Boyd's film diffusion, interparticle diffusion, and intraparticle diffusion models. The isosteric heats of CO2 adsorption using various MOFs are in the range 20–65 kJ mol−1 observing differences in adsorption capacities between 1.15 and 4.72 mmol g−1 at different temperatures due to the electrostatic interactions between CO2 and extra-framework metal ions. The isosteric heat of adsorption calculation in this report, which accounts for the unexpectedly high heat released from Zr-UiO-66-PDC, is finally represented as an increase in the interaction of CO2 with the PDC linker and an increase in Qst with defects. [ABSTRACT FROM AUTHOR]

Macroporous resins are employed for the purification of polyphenolic extracts. However, the relationship between the adsorption and desorption and the textural properties remains unexplored. Thus, we evaluated the textural properties of HP-20, XAD-16 and SP-825 resins and their impact on adsorption and desorption of specific polyphenols like gallic acid, epigallocatechin, and procyanidin B2. The HP-20 resin exhibited a type II isotherm with macroporous structure, while XAD-16 and SP-825 resins displayed type IV isotherms, typically associated with mesoporous materials. The HP-20 resin demonstrated superior adsorption capacity and rupture points for epigallocatechin (2.37 mg/g, 124 min) and procyanidin B2 (1.29 mg/g, 136 min) compared to SP-825 and XAD-16. Contrary, the SP-825 resin exhibited the highest adsorption capacity (5.34 mg/g) and rupture point (68 min) for gallic acid. However, the desorption was more efficient when HP-20 resin was used for all specific polyphenols. Therefore, for an efficient purification process is necessary to consider the chemical structure of the polyphenol and the textural properties. [ABSTRACT FROM AUTHOR]

Ibuprofen (IBP) and diclofenac (DFC) are two of the most commonly used non-steroidal anti-inflammatory drugs (NSAIDs) to treat inflammation and pain. However, they can impact the environment if not treated adequately before discharge into waterways. Biodegradation through the nitrification process is an alternative to reducing the concentration of these micropollutants (MPs) in wastewater. Thus, this work aimed to evaluate the effect of natural zeolite on IBP and DFC removal in a nitrifying batch reactor. Mini-reactors were set up with 90 mL of inoculum and 110 mL of synthetic wastewater with a concentration of 25 mg total ammonia nitrogen TAN/L, at 25 °C and 1 vvm (volume of air/volume liquid∙min) of aeration. Two conditions were tested: high concentrations (IBP = 700 μg/L, DFC = 100 μg/L) and low concentrations (IBP = 30 μg/L, DFC = 20 μg/L). The research used a concentration of 5 g/L of the natural zeolite. Results indicated that the zeolite negatively affected the nitrification rate. At high MPs concentration, the natural zeolite negatively affects the removal of IBP and DFC, where biodegradation and sorption are the mechanisms that eliminate both NSAIDs. Conversely, at low DFC and IBP concentrations, the natural zeolite improves the removal of IBP and DFC, wherein biodegradation is the primary removal mechanism. [ABSTRACT FROM AUTHOR]

The catalytic performance of Ru impregnated perovskites‐based catalysts (Ru/SrZrO3 and Ru/BaZrO3) in the conversion of levulinic acid (LA) into higher valuable chemicals was carried out at different reaction temperatures. The Ru/SrZrO3 and Ru/BaZrO3 catalysts, with a loading of 2.0 Ru atoms nm−2, were prepared by incipient impregnation, and characterized by different techniques. The characterization results indicate presence of dispersed Ru catalysts, with a crystalline structure, with absence of carbonate species for Ru/SrZrO3 and larger carbonates as segregated phase and with stronger basic sites for Ru/BaZrO3. At higher reaction temperatures (200 °C – 250 °C), the higher strength of the basic sites of Ru/BaZrO3 had a direct influence on the levulinic acid (LA) conversion reaction. Differences in the apparent activation energy (Eap) values follow the same trend. The catalysts produce a 100 % of selectivity towards GVL. The formation of GVL was proposed to proceed via the intermediacy of 4‐hydroxypentanoic acid due to the presence of basic surface sites. [ABSTRACT FROM AUTHOR]

The effect of partial substitution of La by Ca and Sr in the catalytic activity of lanthanum cobaltite (LaCoO3) was studied. Two series of La1−xCaxCoO3 and La1−xSrxCoO3 (x = 0, 0.2, and 0.4) reduced perovskites were prepared, characterized and evaluated in the succinic acid conversion at 200 °C and 6 MPa. The characterization results showed a larger Ca substitution in the La1−xCaxCoO3 series, whereas carbonates as segregated phases up to x = 0.2 of Sr were obtained in the La1−xSrxCoO3 series. In the Sr substituted perovskites, the oxidation of Co3+ to Co4+ neutralizes the electronic instability, whereas in the Ca substituted perovskites the presence of Ca2+ generates oxygen vacancies. The succinic acid conversion forms mainly succinic anhydride and 2-hydroxy-tetrahydrofuran by dehydration and hydrogenation processes. The highest initial rate of the reduced LaCoO3 was attributed to the smallest Co crystal size with no segregated phases, compared to substituted catalysts. [ABSTRACT FROM AUTHOR]

The effect of support on the formation of rhenium carbide in the hydrodeoxygenation (HDO) of guaiacol as a lignin-derived compound was evaluated. Catalysts were prepared by incipient wetness impregnation, carburized at 650 °C under a mixture 25/75 of ethylene/hydrogen, and characterized by XRD, N2-physisorption, TPR, TPD of NH3 or isopropylamine (IPA), and XPS. The results have demonstrated that the support choice affects the carburization of rhenium. Indeed, over non-acidic support (e.g., SiO2), limited carburization of the metal was observed, while over ZrO2 and Al2O3, carburization of rhenium occurred, and different carbidic species were obtained depending on the surface and chemical identity of the support. The rhenium carbide species obtained over ZrO2 was the most active and selective toward benzene (22% at 98% of conversion). [ABSTRACT FROM AUTHOR]

Molybdenum supported over activated carbon has been carburized under carbothermal hydrogen reduction conditions at different temperatures in order to modify the carburization degree. The resulting catalysts were characterized by N2 physisorption, CO chemisorption, XPS, TPR, and TPD-NH3 and compared in the hydrodeoxygenation of guaiacol in a batch reactor as a lignin-derived model compound. The results have shown that the CO produced during the TPR could be related to the CO chemisorbed and the carburization degree of the material. The carburization degree was shown to increase with the final temperature, and under such conditions, two different Mo species, Mo4+ and Mo3+, were identified in the oxycarbide phase. Catalytic results showed that the Mo2C is less active than the oxycarbide MoOxCy phase. Mo2C showed to improvement in the transalkylation reactions while in the case of MoOxCy, Mo4+ promotes the hydrogenolysis of catechol to benzene while the Mo3+ species was shown to activate hydrogenation reactions. [ABSTRACT FROM AUTHOR]

With the purpose of obtaining inexpensive electrodes for the degradation of organic pesticides by the electro-Fenton reaction, the required H2O2 being obtained by the 2-electron reduction of dissolved O2, we have prepared glassy carbon electrodes coated with a mixture of graphite with Mo- and/or Co-modified zeolites. Three zeolites were used, Linde type A (ZA), Faujasite (ZY), and MFI (ZSM5), whose maximum possible cation exchange, directly given by the Al/Si ratio, and their hydrophilicity increases in the order ZSM5 < ZY < ZA. The zeolites were modified with Mo and/or Co by the wet impregnation method and characterized by different techniques. The outer surfaces of the three Mo-modified zeolites showed Mo-containing grains (in ZA) or needles (in ZY and ZSM5), which could be largely washed away with hot water. Electrodes were made by depositing on a disc of glassy carbon (GC) a mixture of graphite, zeolite, and a binder. Quite unexpectedly, the cyclic voltammograms (CVs) of the three Mo-modified zeolites showed at least five pairs of anodic-cathodic peaks, which we assume are due to the presence of the Mo7O246− isopolyoxomolybdate anion, proceeding from the impregnating solution, and anchored on the zeolites' surface. With a rotating ring-disc electrode, the highest efficiency for H2O2 production at − 0.2 VRHE, namely, 12.7%, was obtained with the GC/graphite-(CoMo-exchanged ZA) electrode, but this efficiency decreased with time. On the contrary, the three zeolites modified only with Mo were stable in 4-h electrolyses at − 0.2 VRHE and yielded the highest H2O2 concentrations, which we attribute to the Mo7O246− isopolyoxomolybdate anchored on the zeolites. The H2O2 yield was the same for the three Mo-modified zeolites, irrespective of their exchange capacity and hydrophobic/hydrophilic character.Glassy carbon electrodes coated with a mixture of graphite with Mo- and/or Co-modified zeolites have been prepared in order to obtain H2O2 by the 2-electron reduction of dissolved O2. The voltammograms of the Mo-modified zeolites showed five pairs of anodic-cathodic peaks, which we attribute to the presence of the Mo7O246− anion. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ni-reduced nanoparticles were prepared from La1−x Ce x NiO3 perovskite-type oxides. [•] Catalysts displayed a high conversion of guaiacol. [•] Cyclohexanol compound was the main product. [•] Selectivity was unaffected by variation in Ce content of the perovskite catalysts. [ABSTRACT FROM AUTHOR]

Abstract: The Fischer–Tropsch synthesis reaction using a simulated gas mixture, comparable to that obtained from biomass transformation (biosyngas), was studied over LaFe1−x Co x O3 perovskites. The perovskites were prepared using the amorphous citrate precursor method and the FTS reaction was carried out in a stainless steel fixed bed reactor at 300°C and 1MPa. Nitrogen adsorption was at −196°C. Thermal-programmed reduction (TPR), X-ray diffraction (XRD), Fourier-transform IR spectroscopy (FTIR), oxygen-temperature-programmed desorption (O2-TPD) and scanning electron microscopy (SEM) were used as characterization methods. The perovskites were found to display two crystal systems determined by XRD patterns, orthorhombic for x Co <0.5 and rhombohedral for x Co ≥0.5. The LaFe1−x Co x O3 perovskites, with a substitution degree x Co =0.1, 0.2 and 1.0, displayed significant intrinsic CO conversion. This activity was probably due to the formation of Co–metal segregates on the surface, as suggested by XRD patterns. The highest CO intrinsic conversion was obtained for perovskites with a substitution degree of x Co =0.2. The LaFe1−x Co x O3 perovskites presented a wide distribution of liquid hydrocarbons (C6–C18+) and high CH4 formation. The liquid product distribution was related to the average size of iron particles. The increase of cobalt particle size favours the formation of hydrocarbons centred in C8–9 chain length. [Copyright &y& Elsevier]

The unstable proteins in white wine cause haze in bottles of white wine, degrading its quality. Thaumatins and chitinases are grape pathogenesis-related (PR) proteins that remain stable during vinification but can precipitate at high temperatures after bottling. The white wine protein stabilization process can prevent haze by removing these unstable proteins. Traditionally, bentonite is used to remove these proteins; however, it is labor-intensive, generates wine losses, affects wine quality, and harms the environment. More efficient protein stabilization technologies should be based on a better understanding of the main factors and mechanisms underlying protein precipitation. This review focuses on recent developments regarding the instability and removal of white wine proteins, which could be helpful to design more economical and environmentally friendly protein stabilization methods that better preserve the products´ quality. [ABSTRACT FROM AUTHOR]

Nickel-cobalt bimetallic catalysts supported on high surface area graphite with different Ni:Co ratios (3:1, 2:1 and 1:1) and the monometallic Ni and Co were prepared by wetness impregnation method. The catalysts were tested in hydrodeoxygenation (HDO) of guaiacol in the liquid phase at 50 bar of H2 and 300 °C. The materials were characterized by N2 adsorption–desorption, XRD, TEM/STEM, H2-TPR, and CO-chemisorption to assess their properties and correlate them with the catalytic results. The activity was higher on the bimetallic catalysts and followed the trend NiCo2:1/G ∼ NiCo3:1/G > NiCo1:1/G > Co/G > Ni/G. Also, selectivity results showed that Ni was more active in the hydrogenation favoring cyclohexanol production from phenol, while this was inhibited on the Co-containing catalysts. Hence, the results showed that synergy was created between Ni and Co and that their interaction, properties, and catalytic performance depend on the metals' ratio. [ABSTRACT FROM AUTHOR]