Topics in Catalysis最新文献

The objective was to evaluate the non-modified (CN) and calcined (CC) clinoptilolite as catalysts of the in-situ co-pyrolysis of Sargassum biomass and high-density polyethylene (HDPE). Both CN and CC were utilized to enhance the pyrolysis reactions, aiming to upgrade the quality of the resulting byproducts. The potential applications of these byproducts for soil remediation, biofuel and pharmaceutical purposes were also discussed. The feedstock materials and byproducts were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), temperature-programmed desorption of ammonia (TPD-NH₃), and gas chromatography coupled to mass spectrometry (GC–MS). Calcination of CN at 550 °C for 5 h resulted in a 74% reduction in the number of acid sites, a 40% decrease in crystallinity, and a 1.2-fold reduction in surface area, while the Si/Al ratio and pore size distribution remained largely unchanged. The incorporation of HDPE and catalysts increased the conversion rate of Sargassum from 59% to 73%, facilitated by decarboxylation, dehydration, and secondary cracking reactions. Concerning the oil byproduct, the CN catalyst improved its composition by increasing the yield of aliphatic hydrocarbons to 41.8% and reducing sulfur and oxygenated compounds. Conversely, the CC catalyst enhanced the gas byproduct by promoting the production of light hydrocarbons compounds (1.7 mol/kg) and methane (1.5 mol/kg). The resulting solid residual byproduct (biochar) from all tests exhibited sulfur and nitrogen content, and adsorption properties suitable for agricultural soil remediation. Utilizing cost-effective natural catalysts in the co-pyrolysis of Sargassum and HDPE optimizes the recovery of two marine wastes that pose ecological risks in the Caribbean.

A six-step synthesis to (+)-nebivolol ((S,R,R,R)-nebivolol or d-nebivolol) in a cumulative yield of 32% has been developed. Conventional use of diazo compounds has been replaced with a novel approach of sulphur ylide for a safer one-carbon chain extension of methyl 6-fluorochromane-2-carboxylate, which entailed the formation of racemic 2-[dimethyl(oxido)-λ6-sulfanylidene]-1-(6-fluoro-3,4-dihydro-2H-chromen-2-yl)ethenone from methyl 6-fluorochromane-2-carboxylate in high yield. Subsequently the β-keto sulfoxonium ylide was converted into 2-chloro-1-(6-fluorochroman-2-yl)ethanone. Reduction of 2-chloro-1-(6-fluorochroman-2-yl)ethanone to 2-chloro-1-(6-fluorochroman-2-yl)ethanol was catalyzed by Ketoreductase 228 from Syncozymes and resulted in halohydrins (R)-2-chloro-1-((S)-6-fluorochroman-2-yl)ethanol and (S)-2-chloro-1-((S)-6-fluorochroman-2-yl)ethanol in 92% yield. The halohydrins were separated by preparative HPLC. (S)-2-Chloro-1-((S)-6-fluorochroman-2-yl)ethanol underwent amination to produce (R)-2-amino-1-((S)-6-fluorochroman-2-yl)ethanol. The final synthesis step involved reaction of (R)-2-amino-1-((S)-6-fluorochroman-2-yl)ethanol and (R)-2-chloro-1-((S)-6-fluorochroman-2-yl)ethanol forming (+)-nebivolol with > 99% enantiomeric excess (ee).

Arylhydrazone ligands Hsal-bzh (I), Hcsal-bzh (II), Hbsal-bzh (III), and Hnsal-bzh (IV) were synthesized using ethyl benzoate, hydrazine hydrate, salicylaldehyde and its 5-substituted –Cl, –Br, and –NO₂ derivative from refluxing methanol. Carefully characterized ligands I-IV, were reacted with appropriate vanadium precursor to isolate the oxidomethxidovanadium(V) complexes [VO(sal-bzh)(CH₃OH)(OCH₃)] (1), [VO(csal-bzh)(CH₃OH)(OCH₃)] (2), [VO(bsal-bzh)(CH₃OH)(OCH₃)] (3) and [VO(nsal-bzh)(CH₃OH)(OCH₃)] (4) as well as dioxidovanadium(V) complexes K[V^VO₂(sal-bzh)] (5), K[V^VO₂(csal-bzh)] (6), K[V^VO₂(bsal-bzh)] (7) and K[V^VO₂(nsal-bzh)] (8). A number of techniques like ⁵¹V NMR, ¹H NMR, ¹³C NMR, single crystal X-ray analysis, HR-MS analysis were performed to confirm the molecular structure of the vanadium(V) complexes in solid state as well as in solution. Dioxidovanadium(V) complexes 5–8 show good catalytic performance towards the homogeneous epoxidation of a series of olefins with high TOF values. Electron-rich and sterically accessible olefins indene exhibit the highest substrate conversion (94%) with very high TOF values of 3.032 × 10³ h⁻¹, and the least reactivity is observed in electronically poor allylbenzene. Generally, catalysts with the electron-withdrawing group at the 5-position of salicylaldehyde in 6–8 exhibit marginally better performance than catalysts with unsubstituted salicylaldehyde. During the catalytic reaction, the formation of oxidoperoxymonocarbonatevanadium(V) {[V^VO₂(OCO₃H)(nsal-bzh)] + H} intermediate, which is supposed to be the key component for epoxidation, was identified by ⁵¹V NMR and confirm by HR-MS analysis.

This study focuses on the fabrication and characterization of ZrO₂‒TiO₂ mixed oxides modified with gallium and surfactants and their potential application as supports for NiW hydrodesulfurization (HDS) catalysts. The mixed oxides were synthesized via the soft template sol‒gel method with the incorporation of triblock copolymers as surfactants (P123 and L64). We focus on the incorporation of gallium into the supports to modify their surface properties and acidity. The NiW catalysts were evaluated in the HDS of dibenzothiophene (DBT) under high pressure conditions. The results demonstrated that the incorporation of surfactants induced an increase in surface area and an improvement in pore structure within the oxides, which in turn led to enhanced dispersion of the active phases. Additionally, gallium facilitated the sulfidation of the W species and the formation of the NiWS active phase. The catalytic test demonstrated that the catalyst prepared with surfactants, particularly the NiW/ZT-P-Ga catalyst, exhibited the highest initial reaction rates and selectivity toward the hydrogenation pathway. The study demonstrated that the combination of surfactants and gallium ions in the preparation of ZrO₂–TiO₂ supports can significantly enhance the performance of NiW catalysts for deep desulfurization. These findings contribute to the development of more efficient catalysts for industrial HDS processes, addressing the challenges posed by refractory sulfur compounds in fuels.

In this work, it is reported the physicochemical characterization and photocatalytic activity evaluation of TiO₂ thin films modified with Eu, Pd, Fe and Bi. Several characterization techniques were used to investigate thin film properties. The chemical composition as well as the chemical environment of the elements present were determined by X-ray photoelectron spectroscopy (XPS). The crystalline structure was characterized by X-ray diffraction (XRD) and micro-Raman spectroscopy (RS) whereas the optical band gap was determined using UV-Vis spectroscopy. The photocatalytic activity was evaluated in the degradation of the Malachite Green (MG) dye using simulated sunlight. It was found that films modified with Fe and Pd reached MG degradations close to 64.7 and 58.1% after 180 min of reaction. Additionally, thin films were photocatalytically evaluated under UV light (λ=254 nm) using wastewater containing diclofenac (DCF). The best catalytic performance (44% was reached by the film modified with Fe followed by the films modified with Pd (39%) and Bi (38%). To identify the role of reactive species for degradation of MG and DCF, triethanolamine (TEOA), isopropyl alcohol (IPA), ascorbic acid (AA) and benzoquinone (BZQ) were employed as scavenger’s molecules. The results obtained revealed that the O₂^• radical is the reactive specie that mainly contributes to the MG and DCF degradation.

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We report the defluorination of the per- and polyfluoroalkyl substances (PFAS) chemical perfluorooctane sulfonate (PFOS) by deep ultraviolet light assisted electrocatalysis, using the industrial thermoelement materials Constantan and Nichrome as anodes. Surface analysis of wire anodes after anodic conditioning in aqueous base, which enabled uptake of incidental iron from the electrolyte, showed the in situ formation of surface nickel–iron (oxy)hydroxides, which are active electrocatalysts for PFOS defluorination. The defluorination activity of Constantan wire was higher than that of Nichrome wire, which was unstable under PFOS defluorination conditions. Constantan wire mesh completely defluorinated PFOS over a 48-hour period, maintaining 85.5% defluorination after 120 h. The decrease in PFOS defluorination efficiency was attributed to an increase in charge transfer resistance due to the buildup of transition metal hydroxides, oxyhydroxides, or oxides on the wire surface, rather than anode dissolution. Our results provide necessary mechanistic insights into the stability of commercially widely available nickel alloys for the development of economically viable aqueous PFAS remediation systems.

Potassium hexatitanate K₂Ti₆O₁₃ material was successfully synthesized by the sol-gel method. Silver was incorporated in different concentrations from 0.1 to 0.7 wt% by photo-deposition method. The Ag-K₂Ti₆O₁₃ composites were characterized by XRD, SEM, EDX, N₂ physisorption, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, and Mott-Schottky electrochemical test. The X-ray diffraction analysis showed an almost pure monoclinic crystalline phase of the K₂Ti₆O₁₃ with a preferential orientation in the plane (3 1 −1). Morphological characterization showed non-well-defined rod particles. The band-gap value for all the materials was 3.35 eV, while PL spectra showed a lower recombination rate of the photogenerated charges in Ag-KTO materials. The point of zero charge was also determined, resulting in pH values of 7.2 and 8.4 for K₂Ti₆O₁₃ and Ag-K₂Ti₆O₁₃ respectively. Catalysts with a lower content of silver show a higher density of positive holes generated with the irradiation of the semiconductor, consequently, these materials exhibited better photocatalytic activity towards the ketoprofen degradation. The results indicate that ketoprofen was completely degraded on 30 min of reaction generating several intermediate organic products that reached a maximum at 15 min, and 82% of all the organic compounds were mineralized in 5 h of reaction.

With increasing CO₂ pollution, the environment around us changes, necessitating our adaptation to these new conditions. A significant milestone in solving the environmental crisis would be the so-called hydrogen economy. However, this concept still faces substantial challenges as the required catalytic reactions show sluggish efficiency behaviors. To develop new generations of active electrocatalysts for those reactions better understanding of the nature of active sites is required. In 2017, Pfisterer et al. [1] demonstrated the power of tunneling current-noise analysis in electrochemical scanning tunneling microscopy (n-EC-STM) to detect active centers under reaction conditions. In this work, a new analytical tool has been developed to further enhance the distinction of active domains on catalytic surfaces. Additionally, an “activity curve” is introduced to achieve enhanced data representation. Several illustrative examples related to the reactions important for energy provision are presented.

This work aimed to assess and model the kinetics of bisphenol-S (BPS) removal and mineralization achieved by photo-Fenton-like treatment catalyzed by Cu₂O/Al₂O₃. For this purpose, Cu₂O nanoparticles were prepared by Laser Ablation in Liquid (LAL) and supported on commercial Al₂O₃ powder to be used as catalyst in the degradation of bisphenol S (BPS) via a photo-Fenton-like oxidation process. The produced nanoparticles were characterized by Transmission Electronic Microscopy (TEM) and determined to have an average size of 11 nm. For reference, the BPS removal was also monitored and modelled under photolysis with UV-C and UV-C plus H₂O₂. It was found that the experimental data for both BPS concentration and total organic carbon (TOC), are well fitted by a first-order kinetic model. Regarding temporal BPS concentration profiles, the pseudo-first order kinetic constant values were 0.961, 0.402 and 0.035 min⁻¹ for photo-Fenton, UV-C + H₂O₂ and photolysis, respectively; while for the temporal TOC concentration profiles the estimated pseudo-first order kinetic constant values were 0.086, 0.026 and 0.021 min⁻¹ for photo-Fenton, UV-C + H₂O₂ and photolysis, respectively. The effect of Cu content was also studied in the range of 0 to 2%. The kinetic constant was found to be approximately twice with the 2% Cu₂O/Al₂O₃ system than with the 0.5% Cu content, for both cases, temporal BPS concentration and TOC profiles. Thus, it was concluded that the prepared 2%Cu₂O/Al₂O₃ system is an excellent alternative to catalyze H₂O₂ dissociation and conduct BPS mineralization by a photo-Fenton like process which leads to a near complete mineralization, ca. 94% in 30 min.

We discuss activation and reaction of CO₂ on oxide-supported Au nanoparticles in connection with the preparation and characterization of model systems for heterogeneous catalysts, referring mostly to our own studies in the field. These systems are based on crystalline oxide thin films grown on metal substrates, which allows us to characterize them at the atomic scale. Depending on preparation conditions, the oxide-supported Au nanoparticles assume a particular morphology that is largely controlled by electron transfer from the metal substrate through the oxide film or from dopants in the oxide film. If such an electron transfer to the Au nanoparticles is possible, they assume a two-dimensional morphology and electrons can flow from the particle rim to attached CO₂ molecules. This electron transfer leads to the formation of oxalate species that may spill over to the oxide substrate and are available for further reactions. The required structural parameters and the possibilities to monitor the spill-over process are discussed in detail in this paper.