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Catalysts, Volume 10, Issue 4 (April 2020) – 108 articles

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Cover Story (view full-size image) Solution combustion synthesis was used to produce a catalyst with a junction between β-Bi2O3, TiO2 [...] Read more.
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Open AccessReview
Two-Dimensional Materials and Composites as Potential Water Splitting Photocatalysts: A Review
Catalysts 2020, 10(4), 464; https://doi.org/10.3390/catal10040464 - 24 Apr 2020
Viewed by 547
Abstract
Hydrogen production via water dissociation under exposure to sunlight has emanated as an environmentally friendly, highly productive and expedient process to overcome the energy production and consumption gap, while evading the challenges of fossil fuel depletion and ecological contamination. Various classes of materials [...] Read more.
Hydrogen production via water dissociation under exposure to sunlight has emanated as an environmentally friendly, highly productive and expedient process to overcome the energy production and consumption gap, while evading the challenges of fossil fuel depletion and ecological contamination. Various classes of materials are being explored as viable photocatalysts to achieve this purpose, among which, the two-dimensional materials have emerged as prominent candidates, having the intrinsic advantages of visible light sensitivity; structural and chemical tuneability; extensively exposed surface area; and flexibility to form composites and heterostructures. In an abridged manner, the common types of 2D photocatalysts, their position as potential contenders in photocatalytic processes, their derivatives and their modifications are described herein, as it all applies to achieving the coveted chemical and physical properties by fine-tuning the synthesis techniques, precursor ingredients and nano-structural alterations. Full article
(This article belongs to the Special Issue Towards Green, Enhanced Photocatalysts for Hydrogen Evolution)
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Open AccessFeature PaperArticle
Free Radical Photopolymerization and 3D Printing Using Newly Developed Dyes: Indane-1,3-Dione and 1H-Cyclopentanaphthalene-1,3-Dione Derivatives as Photoinitiators in Three-Component Systems
Catalysts 2020, 10(4), 463; https://doi.org/10.3390/catal10040463 - 24 Apr 2020
Cited by 2 | Viewed by 349
Abstract
The design of photoinitiating systems with excellent photochemical reactivities at 405nm LED is one of the obstacles to efficiently promote free radical polymerization in mild conditions (e.g., low light intensity, under air). Here, our actual search for new multicomponent photoinitiating systems at 405nm [...] Read more.
The design of photoinitiating systems with excellent photochemical reactivities at 405nm LED is one of the obstacles to efficiently promote free radical polymerization in mild conditions (e.g., low light intensity, under air). Here, our actual search for new multicomponent photoinitiating systems at 405nm LED prompts us to develop new dyes based on push–pull structures. In the present paper, we chose two series of new dyes which possess indane-1,3-dione and 1H-cyclopenta naphthalene-1,3-dione groups as the electron-withdrawing groups, since they have the great potential to behave as sensitive and remarkable photoinitiators in vat photopolymerization/3D printing. When incorporated with a tertiary amine (ethyl dimethylaminobenzoate EDB, used as electron/hydrogen donor) and an iodonium salt (used as electron acceptor) as the three-component photoinitiating systems (PISs), and among a series of 21 dyes, 10 of them could efficiently promote the free radical photopolymerization of acrylates. Interestingly, steady state photolysis experiments revealed different behaviors of the dyes. Fluorescence experiments and free energy change calculations for redox processes were also carried out to investigate the relevant chemical mechanisms. Additionally, the formation of radicals from the investigated PISs was clearly observed by electron spin resonance (ESR) spin-trapping experiments. Finally, stereoscopic 3D patterns were successfully fabricated by the laser writing technique. In this work, the use of push–pull dyes based on the naphthalene scaffold as photoinitiators of polymerization is reported for the first time in a systematic study aiming at investigating the structure–performance relationship for irradiation carried out at 405 nm. By carefully selecting the electron donors used in the two series of push–pull dyes, novel and high-performance photoinitiating systems operating at 405 nm are thus proposed. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)
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Open AccessFeature PaperArticle
In Situ Raman Spectroscopy as a Tool for Discerning Subtle Structural Differences between Commercial (Ce,Zr)O2-Based OSC Materials of Identical Composition
Catalysts 2020, 10(4), 462; https://doi.org/10.3390/catal10040462 - 24 Apr 2020
Viewed by 292
Abstract
In situ Raman spectroscopy was used at temperatures in the 50–480 °C range under oxidizing (20% O2/He) and reducing (5% H2/He) flowing gas atmospheres to compare the spectra obtained for a series of industrial rare earth doped Cex [...] Read more.
In situ Raman spectroscopy was used at temperatures in the 50–480 °C range under oxidizing (20% O2/He) and reducing (5% H2/He) flowing gas atmospheres to compare the spectra obtained for a series of industrial rare earth doped CexZr1−xO2−δ oxygen storage capacity (OSC) mixed metal oxide materials of identical at % composition, which were prepared by the same chemical synthesis route, in which one synthesis parameter of the aqueous chemistry was slightly varied. The Raman fingerprint of the anionic sublattice is very sensitive to O atom relocations within the bulk of the material matrix and to the pertinent defect topology in each case. A protocol of sequential Raman measurements and analysis was proposed to discern subtle differences between the oxygen vacancy and defect topologies of the examined materials. It can be concluded that for two materials under comparison for their structures, identical Raman spectra are obtained only if the procedures followed for their preparation are identical; a slight variation of one single parameter (e.g., in the aqueous chemistry stage) results in discernible differences in the Raman spectra. The proposed procedure can serve as a tool for proving or disproving infringement of IPR (Intellectual Property Rights) protected preparation methods of ceria-based mixed metal oxide materials. Full article
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Open AccessArticle
Synergy Effects of Cobalt Oxides on Ni/Co-Embedded Al2O3 for Hydrogen-Rich Syngas Production by Steam Reforming of Propane
Catalysts 2020, 10(4), 461; https://doi.org/10.3390/catal10040461 - 24 Apr 2020
Viewed by 250
Abstract
The synergetic effects of Co oxides on the Ni/CoAl (NCA) catalysts were observed at an optimal molar ratio of Al/Co = 2 (NCA(2)) due to the partial formations of thermally stable spinel CoAl2O4 phases for the steam reforming of propane [...] Read more.
The synergetic effects of Co oxides on the Ni/CoAl (NCA) catalysts were observed at an optimal molar ratio of Al/Co = 2 (NCA(2)) due to the partial formations of thermally stable spinel CoAl2O4 phases for the steam reforming of propane (SRP). The optimal content of the spinel CoAl2O4 phases on the NCA(2) was responsible for the formation of the relatively active oxophilic metallic Co nanoparticles with a smaller amount of less active NiAl2O4 on the surfaces by preserving the relative amount of metallic Co of 68% and 52% in the reduced and used catalysts, which enhanced the catalytic activity and stability with the largest specific rate of 1.37 C3H8/(Ni + Co)h−1 among the tested NCA catalysts. The larger or smaller amounts of Co metal on the less active NCA mainly caused the preferential formation of larger aggregated Ni nanoparticles ~16 nm in size due to their weaker interactions, or induced the smaller formations of active metal phases by selectively forming the spinel NiAl2O4 phases with ~60% in the NCA(4), resulting in a fast deactivation. Full article
(This article belongs to the Special Issue Catalytic Steam Reforming)
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Open AccessArticle
N-Halosuccinimides as Precatalysts for C-, N-, O-, and X-Nucleophilic Substitution Reactions of Alcohols under Mild Reaction Conditions
Catalysts 2020, 10(4), 460; https://doi.org/10.3390/catal10040460 - 24 Apr 2020
Viewed by 310
Abstract
N-halosuccinimides (chloro, bromo, and iodo, respectively) were introduced, tested, and applied as efficient and non-metal precatalysts for C-, N-, O-, and X-nucleophilic substitution reactions of alcohols under solvent-free reaction conditions (SFRC) or under high substrate concentration reaction conditions [...] Read more.
N-halosuccinimides (chloro, bromo, and iodo, respectively) were introduced, tested, and applied as efficient and non-metal precatalysts for C-, N-, O-, and X-nucleophilic substitution reactions of alcohols under solvent-free reaction conditions (SFRC) or under high substrate concentration reaction conditions (HCRC) efficiently and selectively, into the corresponding products. Full article
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Open AccessArticle
Laccase Immobilized Fe3O4-Graphene Oxide Nanobiocatalyst Improves Stability and Immobilization Efficiency in the Green Preparation of Sulfa Drugs
Catalysts 2020, 10(4), 459; https://doi.org/10.3390/catal10040459 - 23 Apr 2020
Viewed by 222
Abstract
This paper, reports on the novel and green synthesis procedure for sulfonamides that involved the immobilization of Trametes Versicolor laccase onto the Fe3O4–graphene nanocomposite via glutaraldehyde (GA) crosslinking (Lac/Fe3O4/GO). Various parameters, mainly, activation time, GA, [...] Read more.
This paper, reports on the novel and green synthesis procedure for sulfonamides that involved the immobilization of Trametes Versicolor laccase onto the Fe3O4–graphene nanocomposite via glutaraldehyde (GA) crosslinking (Lac/Fe3O4/GO). Various parameters, mainly, activation time, GA, and laccase concentration were investigated and optimized. The results showed that the optimal contact time was 4 h, GA concentration was 5% while laccase concentration was 5 mg·mL−1, at which a high enzyme activity recovery was achieved (86%). In terms of the stability of immobilized laccase to temperature and storage conditions, the performance of the nanobiocatalyst was found to significantly exceed that of free laccase. The results have indicated that nearly 70% of relative activity for immobilized laccase remained after the incubation period of 2 h at 55 °C, but only 48% of free laccase remained within the same time period. Moreover, the immobilized laccase retained 88% of its initial activity after storage for 20 days. In case of the free laccase, the activity retained within the same time period was 32%. In addition, the nanobiocatalyst possessed better recycling performance as evidenced from the observation that after eight cycles of repeated use, it retained 85% of its original activity. Full article
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Open AccessArticle
Simple Environmentally-Friendly Reduction of 4-Nitrophenol
Catalysts 2020, 10(4), 458; https://doi.org/10.3390/catal10040458 - 23 Apr 2020
Viewed by 281
Abstract
The low molecular-mass organic compound 4-nitrophenol is involved in many chemical processes and is commonly present in soils and in surface and ground waters, thereby causing severe environmental impact and health risk. Several methods have been proposed for its transformation (bio and chemical [...] Read more.
The low molecular-mass organic compound 4-nitrophenol is involved in many chemical processes and is commonly present in soils and in surface and ground waters, thereby causing severe environmental impact and health risk. Several methods have been proposed for its transformation (bio and chemical degradation). However, these strategies not only produce equally or more toxic aromatic species but also require harsh operating conditions and/or time-consuming treatments. In this context, we report a comprehensive and systematic study of the electrochemical reduction of 4-nitrophenol as a viable alternative. We have explored the electrochemical reduction of this pollutant over different metallic and carbonaceous substrata. Specifically, we have focused on the use of gold and silver working electrodes since they combine a high electrocatalytic activity for 4-nitrophenol reduction and a low electrocatalytic capacity for hydrogen evolution. The influence of the pH, temperature, and applied potential have also been considered as crucial parameters in the overall optimization of the process. While acidic media and high temperatures favor the clean reduction of 4-nitrophenol to 4-aminophenol, the simultaneous hydrogen evolution is pernicious for this purpose. Herein, a simple and effective electrochemical method for the transformation of 4-nitrophenol into 4-aminophenol is proposed with virtually no undesired by-products. Full article
(This article belongs to the Special Issue Electrocatalysis in Energy and Green Chemistry)
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Open AccessArticle
Sustainable Method for the Synthesis of Alternative Bis(2-Ethylhexyl) Terephthalate Plasticizer in the Presence of Protic Ionic Liquids
Catalysts 2020, 10(4), 457; https://doi.org/10.3390/catal10040457 - 23 Apr 2020
Viewed by 317
Abstract
Inexpensive Brønsted acidic ionic liquids based on trimethylamine and sulfuric acid are proposed as both solvents and catalysts in the synthesis of alternative plasticizer bis(2-ethylhexyl) terephthalate, which has a broad spectrum of applications in plasticization processes. The utilization of 50 mol % of [...] Read more.
Inexpensive Brønsted acidic ionic liquids based on trimethylamine and sulfuric acid are proposed as both solvents and catalysts in the synthesis of alternative plasticizer bis(2-ethylhexyl) terephthalate, which has a broad spectrum of applications in plasticization processes. The utilization of 50 mol % of Brønsted ionic liquid led to the full conversion of terephthalic acid after 8 h of reaction at 120 °C. Additionally, a 100% selectivity of bis(2-ethylhexyl) terephthalate was obtained. The advantage of the presented reaction system is based on the formation of a biphasic system during the reaction. The bottom phase consists of an ionic liquid and water, and the upper phase is created by the ester and unreacted alcohol. This phenomenon helps overcome the equilibrium of the reaction and drives it towards a high yield of product. The presented new approach is proposed as a safe, cost-effective, and alternative method to conventional processes with organometallic compounds that, in turn, leads to greener and a more economically viable technology. Full article
(This article belongs to the Special Issue Ionic Liquids in Catalysis)
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Open AccessFeature PaperArticle
UV-Catalyzed Persulfate Oxidation of an Anthraquinone Based Dye
Catalysts 2020, 10(4), 456; https://doi.org/10.3390/catal10040456 - 23 Apr 2020
Viewed by 297
Abstract
Wastewater from the textile industry has a substantial impact on water quality. Synthetic dyes used in the textile production process are often discharged into water bodies as residues. Highly colored wastewater causes various of problems for the aquatic environment such as: reducing light [...] Read more.
Wastewater from the textile industry has a substantial impact on water quality. Synthetic dyes used in the textile production process are often discharged into water bodies as residues. Highly colored wastewater causes various of problems for the aquatic environment such as: reducing light penetration, inhibiting photosynthesis and being toxic to certain organisms. Since most dyes are resistant to biodegradation and are not completely removed by conventional methods (adsorption, coagulation-flocculation, activated sludge, membrane filtration) they persist in the environment. Advanced oxidation processes (AOPs) based on hydrogen peroxide (H2O2) have been proven to decolorize only some of the dyes from wastewater by photocatalysis. In this article, we compared two very different photocatalytic systems (UV/peroxydisulfate and UV/H2O2). Photocatalyzed activation of peroxydisulfate (PDS) generated sulfate radicals (SO4•−), which reacted with the selected anthraquinone dye of concern, Acid Blue 129 (AB129). Various conditions, such as pH and concentration of PDS were applied, in order to obtain an effective decolorization effect, which was significantly better than in the case of hydroxyl radicals. The kinetics of the reaction followed a pseudo-first order model. The main reaction pathway was also proposed based on quantum chemical analysis. Moreover, the toxicity of the solution after treatment was evaluated using Daphnia magna and Lemna minor, and was found to be significantly lower compared to the toxicity of the initial dye. Full article
(This article belongs to the Special Issue Greener Catalysis for Environmental Applications)
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Open AccessArticle
Preparation and Performances of ZIF-67-Derived FeCo Bimetallic Catalysts for CO2 Hydrogenation to Light Olefins
Catalysts 2020, 10(4), 455; https://doi.org/10.3390/catal10040455 - 23 Apr 2020
Viewed by 333
Abstract
A novel sodium-promoted Fe-Co/NC catalyst prepared by incipient-wet-impregnation method using ZIF-67 as a support was employed to convert CO2 to light olefins through hydrogenation reaction. Properties of the synthesized catalysts calcinated at various temperatures (from 400 to 700 °C) were investigated by [...] Read more.
A novel sodium-promoted Fe-Co/NC catalyst prepared by incipient-wet-impregnation method using ZIF-67 as a support was employed to convert CO2 to light olefins through hydrogenation reaction. Properties of the synthesized catalysts calcinated at various temperatures (from 400 to 700 °C) were investigated by XRD, SEM, TEM and Mӧssbauer spectroscopy. Characterization results showed that the support could be fully converted into carbon support above 500 °C, which could anchor metal particles, thus resulting in a uniform dispersion of active components. Furthermore, the Fe-Co alloy was formed during N2 calcination, and was converted into active components, such as Fe3O4, Fe5C2, and Co2C during the reaction. The reaction result indicated that FeCo/NC-600 catalyst exhibited the highest selectivity of light olefins (C2= − C4=, 27%) and CO2 conversion could reach around 37% when this catalyst pyrolyzed at 600 °C in N2. The highest selectivity for light olefins may be related to the combination of suitable particle size and sufficient active sites of iron carbide. Full article
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Open AccessArticle
Research on Aftertreatment Inlet_Outlet Insulation for A Nonroad Middle Range Diesel Engine
Catalysts 2020, 10(4), 454; https://doi.org/10.3390/catal10040454 - 22 Apr 2020
Viewed by 300
Abstract
Diesel exhaust aftertreatment systems are required for meeting China StageIV emission regulations. This paper addresses an aftertreatment system designed to meet the China StageIV emission standards for nonroad vehicle markets. It presents a comprehensive experimental research work on aftertreatment skin temperature and the [...] Read more.
Diesel exhaust aftertreatment systems are required for meeting China StageIV emission regulations. This paper addresses an aftertreatment system designed to meet the China StageIV emission standards for nonroad vehicle markets. It presents a comprehensive experimental research work on aftertreatment skin temperature and the radiated impact on its neighboring parts in a nonroad vehicle powered by a middle range diesel engine under aftertreatment inlet/outlet with insulation and without insulation with multiple experimental conditions, as well as validating the emission results with these two different aftertreatment configurations. According to the experimental results, it can be observed that the aftertreatment inlet/outlet with insulation and without insulation using a Diesel Oxidant Catalyst (DOC) + Diesel Particle Filter (DPF) + Selective Catalytic Reduction (SCR) scheme could both meet China StageIV emission regulations and the whole vehicle arrangement. The connection pipe is generally short between the aftertreatment and the engine turbo charger on nonroad application vehicles, which results in the exhaust gas temperature of the internal aftertreatment at each point being similar, with variation within ±2% for the aftertreatment inlet/outlet with insulation compared to the aftertreatment inlet/outlet without insulation. The aftertreatment skin temperature differences under these two configurations occur on the inlet module and outlet module, and the skin temperatures of other aftertreatment modules are little impacted. These experimental results also validate the radiation model. All aftertreatment skin temperatures are measured with different experimental conditions. In future, if considering integrating other parts like sensors on the surface of the aftertreatment, the configuration with insulation is recommended. As per the experimental results, the maximum inlet skin temperature can lower nearly 50% with insulation and the maximum outlet temperature could lower about 28% compared to the configuration without inlet/outlet insulation. If taking cost into consideration, the configuration without insulation is suggested. This research also introduces alternative solutions for different concerns for real applications. The methodology provides effective guidance and reference for future aftertreatment insulation considerations for inlet modules and outlet modules on real applications. Full article
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Open AccessArticle
MIL-101(Cr) for CO2 Conversion into Cyclic Carbonates, Under Solvent and Co-Catalyst Free Mild Reaction Conditions
Catalysts 2020, 10(4), 453; https://doi.org/10.3390/catal10040453 - 22 Apr 2020
Viewed by 341
Abstract
Mild reaction conditions (nearly room temperature and atmospheric CO2 pressure) for the cycloaddition of CO2 with epoxides to produce cyclic carbonates were investigated applying MIL-101(Cr) as a catalyst. The MIL-101 catalyst contains strong acid sites, which promote the ring-opening of the [...] Read more.
Mild reaction conditions (nearly room temperature and atmospheric CO2 pressure) for the cycloaddition of CO2 with epoxides to produce cyclic carbonates were investigated applying MIL-101(Cr) as a catalyst. The MIL-101 catalyst contains strong acid sites, which promote the ring-opening of the epoxide substrate. Moreover, the high surface area, enabling the adsorption of more CO2 (substrate), combined with a large pore size of the catalyst is essential for the catalytic performance. Additionally, epoxide substrates bearing electron-withdrawing substituents or having a low boiling point demonstrated an excellent conversion towards the cyclic carbonates. MIL-101(Cr) for the cycloaddition of carbon dioxide with epoxides is demonstrated to be a robust and stable catalyst able to be re-used at least five times without loss in activity. Full article
(This article belongs to the Special Issue State-of-the-Art Catalytical Technology in South Korea)
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Open AccessArticle
Preparation and Characterization of Photoactive Anatase TiO2 from Algae Bloomed Surface Water
Catalysts 2020, 10(4), 452; https://doi.org/10.3390/catal10040452 - 22 Apr 2020
Viewed by 387
Abstract
The purpose of the study was to effectively treat algae bloomed water while using a Ti-based coagulant (TiCl4) and recover photoactive novel anatase TiO2 from the flocculated sludge. Conventional jar tests were conducted in order to evaluate the coagulation efficiency, [...] Read more.
The purpose of the study was to effectively treat algae bloomed water while using a Ti-based coagulant (TiCl4) and recover photoactive novel anatase TiO2 from the flocculated sludge. Conventional jar tests were conducted in order to evaluate the coagulation efficiency, and TiCl4 was found superior compared to commercially available poly aluminum chloride (PAC). At a dose of 0.3 g Ti/L, the removal rate of turbidity, chemical oxygen demand (COD), and total phosphorus (TP) were measured as 99.8%, 66.7%, and 96.9%, respectively. Besides, TiO2 nanoparticles (NPs) were recovered from the flocculated sludge and scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX), and X-ray diffraction (XRD) analysis confirmed the presence of only anatase phase. The recovered TiO2 was found to be effective in removing gaseous CH3CHO and NOx under UV-A lamp at a light intensity of 10 W/m2. Additionally, the TiO2 mixed mortar blocks that were prepared in this study successfully removed atmospheric nitrogen oxide (NOx) under UV irradiance. This study is one of the first to prepare anatase TiO2 from flocculated algal sludge and it showed promising results. Further research on this novel TiO2 concerning internal chemical bonds and shift in the absorbance spectrum could explore several practical implications. Full article
(This article belongs to the Special Issue TiO2 for Photocatalytic Applications)
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Open AccessArticle
The Catalyst Loading Effects on the Feed Rate of NaBH4 Solution for the Hydrogen Production Rate and Conversion Efficiency
Catalysts 2020, 10(4), 451; https://doi.org/10.3390/catal10040451 - 22 Apr 2020
Viewed by 269
Abstract
The research in this study focused on the operating parameters for a high efficiency hydrogen production rate system, with the aim to design a hydrolysis of the NaBH4 hydrogen production module for lightweight and efficient hydrogen production and conversion. The experiment used [...] Read more.
The research in this study focused on the operating parameters for a high efficiency hydrogen production rate system, with the aim to design a hydrolysis of the NaBH4 hydrogen production module for lightweight and efficient hydrogen production and conversion. The experiment used a reactor, where the reaction volume was about 12 mL. The parameters on the feed rate of the NaBH4 solution and the catalyst loading for the hydrogen production rate and conversion efficiency were investigated. The catalyst is sufficient to allow the release of hydrogen in the 1 g/min solution, but the efficiency of hydrogen production at high flow rates has been shown to be low in previous studies. Therefore, the aim is to increase the catalyst to improve the reaction efficiency in this study. The results show that at the high temperature reaction condition, solid NaBO2 will not generate on the catalyst surface to influence the hydrogen production rate when using the five pcs catalyst. When the reaction temperature was 108 °C, the average hydrogen production rate was 1.72 L/min, and the conversion efficiency was 91.2%. Full article
(This article belongs to the Special Issue Thin Film Catalysts for Energy and Environment Utilization)
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Open AccessArticle
Multitarget Evaluation of the Photocatalytic Activity of P25-SiO2 Prepared by Atomic Layer Deposition
Catalysts 2020, 10(4), 450; https://doi.org/10.3390/catal10040450 - 22 Apr 2020
Viewed by 366
Abstract
This work presents the evaluation of the photocatalytic activity of P25 TiO2 particles, coated with SiO2, using atomic layer deposition (ALD) for the photocatalytic removal of methylene blue, oxidation of methanol and inactivation of Escherichia coli bacteria in water and [...] Read more.
This work presents the evaluation of the photocatalytic activity of P25 TiO2 particles, coated with SiO2, using atomic layer deposition (ALD) for the photocatalytic removal of methylene blue, oxidation of methanol and inactivation of Escherichia coli bacteria in water and its comparative evaluation with bare P25 TiO2. Two different reactor configurations were used, a slurry reactor with the catalyst in suspension, and a structured reactor with the catalyst immobilized in macroporous foams, that enables the long-term operation of the process in continuous mode, without the necessity of separation of the particles. The results show that the incorporation of SiO2 decreases the efficiency of the photocatalytic oxidation of methanol, whereas a significant improvement in the removal of methylene blue is achieved, and no significant changes are observed in the photocatalytic inactivation of bacteria. Adsorption tests showed that the improvements, observed in the removal of methylene blue by the incorporation of SiO2, was mainly due to an increase in its adsorption. The improvement in the adsorption step as part of the global photocatalytic process led to a significant increase in its removal efficiency. Similar conclusions were reached for bacterial inactivation where the loss of photocatalytic efficiency, suggested by the methanol oxidation tests, was counteracted with a better adherence of bacteria to the catalyst that improved its elimination. With respect to the use of macroporous foams as support, a reduction in the photocatalytic efficiency is observed, as expected from the decrease in the available surface area. Nevertheless, this lower efficiency can be counteracted by the operational improvement derived from the easy catalyst reuse. Full article
(This article belongs to the Special Issue Novel Heterogeneous Catalysts for Advanced Oxidation Processes (AOPs))
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Open AccessFeature PaperArticle
Highly Active Hydrogenation Catalysts Based on Pd Nanoparticles Dispersed along Hierarchical Porous Silica Covered with Polydopamine as Interfacial Glue
Catalysts 2020, 10(4), 449; https://doi.org/10.3390/catal10040449 - 22 Apr 2020
Viewed by 308
Abstract
New catalysts based on Pd(0) nanoparticles (Pd NPs) on a bimodal porous silica of the UVM-7/polydopamine (PDA) support have been synthesized following two preparative strategies based on the sequential or joint incorporation of two components of the composite (Pd and PDA). We analyzed [...] Read more.
New catalysts based on Pd(0) nanoparticles (Pd NPs) on a bimodal porous silica of the UVM-7/polydopamine (PDA) support have been synthesized following two preparative strategies based on the sequential or joint incorporation of two components of the composite (Pd and PDA). We analyzed the role played by the PDA as ‘interfacial glue’ between the silica scaffold and the Pd NPs. The catalysts were tested for the hydrogenation of 4-nitrophenol using (NEt4)BH4 as the hydrogenating agent. In addition to the palladium content, the characterization of the catalysts at the micro and nanoscale has highlighted the importance of different parameters, such as the size and dispersion of the Pd NPs, as well as their accessibility to the substrate (greater or lesser depending on their entrapment level in the PDA) on the catalytic efficiency. Staged sequential synthesis has led to better catalytic results. The most active Pd(0) centers seem to be Pd NPs of less than 1 nm on the PDA surface. The efficiency of the catalysts obtained is superior to that of similar materials without PDA. A comprehensive comparison has been made with other catalysts based on Pd NPs in a wide variety of supports. The TOF values achieved are among the best described in the literature. Full article
(This article belongs to the Special Issue Bimodal Porous Catalysts)
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Open AccessArticle
C–H Bond Activation of Silyl-Substituted Pyridines with Bis(Phenolate)Yttrium Catalysts as a Facile Tool towards Hydroxyl-Terminated Michael-Type Polymers
Catalysts 2020, 10(4), 448; https://doi.org/10.3390/catal10040448 - 22 Apr 2020
Viewed by 332
Abstract
Herein, silicon-protected, ortho-methylated hydroxy-pyridines were reported as initiators in 2-aminoalkoxy-bis(phenolate)yttrium complexes for rare earth metal-mediated group-transfer polymerization (REM-GTP) of Michael-type monomers. To introduce these initiators, C−H bond activation was performed by reacting [(ONOO)tBuY(X)(thf)] (X = CH2TMS, thf [...] Read more.
Herein, silicon-protected, ortho-methylated hydroxy-pyridines were reported as initiators in 2-aminoalkoxy-bis(phenolate)yttrium complexes for rare earth metal-mediated group-transfer polymerization (REM-GTP) of Michael-type monomers. To introduce these initiators, C−H bond activation was performed by reacting [(ONOO)tBuY(X)(thf)] (X = CH2TMS, thf = tetrahydrofuran) with tert-butyl-dimethyl-silyl-functionalized α-methylpyridine to obtain the complex [(ONOOtBuY(X)(thf)] (X = 4-(4′-(((tert-butyldimethylsilyl)oxy)methyl)phenyl)-2,6-di-methylpyridine). These initiators served as functional end-groups in polymers produced via REM-GTP. In this contribution, homopolymers of 2-vinylpyridine (2VP) and diethyl vinyl phosphonate (DEVP) were produced. Activity studies and end-group analysis via mass spectrometry, size-exclusion chromatography (SEC) and NMR spectroscopy were performed to reveal the initiator efficiency, the catalyst activity towards both monomers as well as the initiation mechanism of this initiator in contrast to commonly used alkyl initiators. In addition, 2D NMR studies were used to further confirm the end-group integrity of the polymers. For all polymers, different deprotection routes were evaluated to obtain hydroxyl-terminated poly(2-vinylpyridine) (P2VP) and poly(diethyl vinyl phosphonate) (PDEVP). Such hydroxyl groups bear the potential to act as anchoring points for small bioactive molecules, for post-polymerization functionalization or as macroinitiators for further polymerizations. Full article
(This article belongs to the Special Issue Catalysts for C–H Activation and Functionalisation)
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Open AccessArticle
Positive Impact of Natural Deep Eutectic Solvents on the Biocatalytic Performance of 5-Hydroxymethyl-Furfural Oxidase
Catalysts 2020, 10(4), 447; https://doi.org/10.3390/catal10040447 - 22 Apr 2020
Viewed by 448
Abstract
Deep eutectic solvents (DESs) have been applied as cosolvents in various biocatalytic processes during recent years. However, their use in combination with redox enzymes has been limited. In this study, we have explored the beneficial effects of several DES as cosolvents on the [...] Read more.
Deep eutectic solvents (DESs) have been applied as cosolvents in various biocatalytic processes during recent years. However, their use in combination with redox enzymes has been limited. In this study, we have explored the beneficial effects of several DES as cosolvents on the performance of 5-hydroxymethylfurfural oxidase (HMFO), a valuable oxidative enzyme for the preparation of furan-2,5-dicarboxylic acid (FDCA), and other compounds, such as carbonyl compounds and carboxylic acids. The use of natural DESs, based on glucose and fructose, was found to have a positive effect. Higher conversions are obtained for the synthesis of several oxidized compounds, including FDCA. Depending on the type of DES, the stability of HMFO could be significantly improved. As the use of DES increases the solubility of many substrates while they only mildly affect dioxygen solubility, this study demonstrates that biocatalysis based on HMFO and other redox biocatalysts can benefit from a carefully selected DES. Full article
(This article belongs to the Section Biocatalysis)
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Open AccessArticle
CeO2 for Water Remediation: Comparison of Various Advanced Oxidation Processes
Catalysts 2020, 10(4), 446; https://doi.org/10.3390/catal10040446 - 21 Apr 2020
Viewed by 361
Abstract
Three different Advanced Oxidation Processes (AOPs) have been investigated for the degradation of the imidacloprid pesticide in water: photocatalysis, Fenton and photo-Fenton reactions. For these tests, we have compared the performance of two types of CeO2, employed as a non-conventional photocatalyst/Fenton-like [...] Read more.
Three different Advanced Oxidation Processes (AOPs) have been investigated for the degradation of the imidacloprid pesticide in water: photocatalysis, Fenton and photo-Fenton reactions. For these tests, we have compared the performance of two types of CeO2, employed as a non-conventional photocatalyst/Fenton-like material. The first one has been prepared by chemical precipitation with KOH, while the second one has been obtained by exposing the as-synthetized CeO2 to solar irradiation in H2 stream. This latter treatment led to obtain a more defective CeO2 (coded as “grey CeO2”) with the formation of Ce3+ sites on the surface of CeO2, as determined by Raman and X-ray Photoelectron Spectroscopy (XPS) characterizations. This peculiar feature has been demonstrated as beneficial for the solar photo–Fenton reaction, with the best performance exhibited by the grey CeO2. On the contrary, the bare CeO2 showed a photocatalytic activity higher with respect to the grey CeO2, due to the higher exposed surface area and the lower band-gap. The easy synthetic procedures of CeO2 reported here, allows to tune and modify the physico-chemical properties of CeO2, allowing a choice of different CeO2 samples on the basis of the specific AOPs for water remediation. Furthermore, neither of the samples have shown any critical toxicity. Full article
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Open AccessCommunication
A Rapid Method for the Selection of Amidohydrolases from Metagenomic Libraries by Applying Synthetic Nucleosides and a Uridine Auxotrophic Host
Catalysts 2020, 10(4), 445; https://doi.org/10.3390/catal10040445 - 21 Apr 2020
Viewed by 348
Abstract
In this study, the development of a rapid, high-throughput method for the selection of amide-hydrolysing enzymes from the metagenome is described. This method is based on uridine auxotrophic Escherichia coli strain DH10B ∆pyrFEC and the use of N4-benzoyl-2’-deoxycytidine as a [...] Read more.
In this study, the development of a rapid, high-throughput method for the selection of amide-hydrolysing enzymes from the metagenome is described. This method is based on uridine auxotrophic Escherichia coli strain DH10B ∆pyrFEC and the use of N4-benzoyl-2’-deoxycytidine as a sole source of uridine in the minimal microbial M9 medium. The approach described here permits the selection of unique biocatalysts, e.g., a novel amidohydrolase from the activating signal cointegrator homology (ASCH) family and a polyethylene terephthalate hydrolase (PETase)-related enzyme. Full article
(This article belongs to the Section Biocatalysis)
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Open AccessArticle
Bimetallic Pd-Au/SiO2 Catalysts for Reduction of Furfural in Water
Catalysts 2020, 10(4), 444; https://doi.org/10.3390/catal10040444 - 20 Apr 2020
Viewed by 349
Abstract
Catalytic systems based on bimetallic Pd-Au particles deposited on SiO2 were prepared by ultrasonically assisted water impregnation and used in the hydrogenation of furfural obtained by the acidic hydrolysis of waste biomass (brewery’s spent grain) in aqueous phase. Pd-Au/SiO2 catalysts containing [...] Read more.
Catalytic systems based on bimetallic Pd-Au particles deposited on SiO2 were prepared by ultrasonically assisted water impregnation and used in the hydrogenation of furfural obtained by the acidic hydrolysis of waste biomass (brewery’s spent grain) in aqueous phase. Pd-Au/SiO2 catalysts containing 50 g of Pd and 2–100 g of Au per 1 kg of catalyst were characterized by high activity in the studied process and, depending on the Pd/Au ratio, selectivity to 2-methyloxolan-2-ol. The modification of 5%Pd/SiO2 by Au leads to the formation of dispersed Au-Pd solid solution phases, which was confirmed by XRD, XPS, ToF-SIMS, SEM-EDS, and H2-TPR techniques. The effect of dilution of surface palladium by gold atoms is probably crucial for modification of the reaction mechanism and formation of 2-methyloxolan-2-ol as the main product. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)
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Open AccessReview
Palladium and Copper Catalyzed Sonogashira cross Coupling an Excellent Methodology for C-C Bond Formation over 17 Years: A Review
Catalysts 2020, 10(4), 443; https://doi.org/10.3390/catal10040443 - 20 Apr 2020
Viewed by 399
Abstract
Sonogashira coupling involves coupling of vinyl/aryl halides with terminal acetylenes catalyzed by transition metals, especially palladium and copper. This is a well known reaction in organic synthesis and plays a role in sp2-sp C-C bond formations. This cross coupling was used [...] Read more.
Sonogashira coupling involves coupling of vinyl/aryl halides with terminal acetylenes catalyzed by transition metals, especially palladium and copper. This is a well known reaction in organic synthesis and plays a role in sp2-sp C-C bond formations. This cross coupling was used in synthesis of natural products, biologically active molecules, heterocycles, dendrimers, conjugated polymers and organic complexes. This review paper focuses on developments in the palladium and copper catalyzed Sonogashira cross coupling achieved in recent years concerning substrates, different catalyst systems and reaction conditions. Full article
(This article belongs to the Special Issue Transition Metal Complexes as Catalysts in Organic Chemistry)
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Open AccessFeature PaperReview
Advances in Designing Au Nanoparticles for Catalytic Epoxidation of Propylene with H2 and O2
Catalysts 2020, 10(4), 442; https://doi.org/10.3390/catal10040442 - 19 Apr 2020
Viewed by 601
Abstract
Au nanoparticles, which can be used in various industrial and environmental applications, have drawn substantial research interest. In this review, a comprehensive background and some insights are provided regarding recent studies concerning the use of Au nanoparticles for catalytic propylene epoxidation with H [...] Read more.
Au nanoparticles, which can be used in various industrial and environmental applications, have drawn substantial research interest. In this review, a comprehensive background and some insights are provided regarding recent studies concerning the use of Au nanoparticles for catalytic propylene epoxidation with H2 and O2. Over the last two decades, substantial progress has been made toward the efficient production of propylene oxide (PO); this includes the design of highly dispersed Au catalysts on Ti-modified mesoporous silica supports, the optimization of catalytic epoxidation, and the determination of the mechanisms and reaction pathways of epoxidation. Particularly, the critical roles of catalyst synthesis, the types of material support, Au nanoparticle sizes, and the dispersion amounts of Au nanoparticles are emphasized in this review. In future studies, novel, practical, robust, and highly PO-selective Au nanoparticle catalyst systems are expected to be continually designed for the enhanced catalytic epoxidation of propylene. Full article
(This article belongs to the Special Issue Sustainable Nanocatalysts for Organic Transformations)
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Open AccessArticle
Preparation of CdS Nanoparticles-TiO2 Nanorod Hererojunction and Their High-Performance Photocatalytic Activity
Catalysts 2020, 10(4), 441; https://doi.org/10.3390/catal10040441 - 19 Apr 2020
Viewed by 268
Abstract
As a new and emerging technology, photocatalytic oxidation is widely used in the fields of sewage treatment and organic pollution control. In this study, CdS nanoparticles were prepared at room temperature by an innovative preparation method, then TiO2 nanorod–CdS nanoparticle heterojunction photocatalysts [...] Read more.
As a new and emerging technology, photocatalytic oxidation is widely used in the fields of sewage treatment and organic pollution control. In this study, CdS nanoparticles were prepared at room temperature by an innovative preparation method, then TiO2 nanorod–CdS nanoparticle heterojunction photocatalysts were prepared using the solvothermal method, with TiCl3 used as the precursor for TiO2 nanorods. This study mainly took advantage of the small size of the CdS nanoparticles in combination with TiO2 nanorods, and the resultant heterojunctions had large specific surface areas, thereby increasing the contact area between the catalysts and the contaminants. In addition, due to the lower band gap energy (2.4 eV) of CdS, the photo response range of the heterojunction photocatalysts was also increased. In an experimental study, through photocatalytic performance tests of the catalysts with different weight ratios, it was found that the TiO2(40%)@CdS composite had the best photocatalytic performance and the highest catalytic rate. BET, SEM, and other tests showed that the specific surface area of the TiO2(40%)@CdS composite was the largest. TiO2 nanorods and CdS particles were uniformly distributed in the composite, and the optical response range was extended to the visible light region. Full article
(This article belongs to the Special Issue Photocatalysis in the Wastewater Treatment)
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Open AccessArticle
Electrocatalytic Glucose Oxidation at Coral-Like Pd/C3N4-C Nanocomposites in Alkaline Media
Catalysts 2020, 10(4), 440; https://doi.org/10.3390/catal10040440 - 19 Apr 2020
Viewed by 343
Abstract
Porous coral-like Pd/C3N4-C nanocomposites are fabricated by a simple one-pot chemical reduction method. Their electrocatalytic performance is ~50% higher than a carbon-loaded palladium electrocatalyst (Pd/C) in alkaline media. This confirms that the glucose electrooxidation and sensing performance of a [...] Read more.
Porous coral-like Pd/C3N4-C nanocomposites are fabricated by a simple one-pot chemical reduction method. Their electrocatalytic performance is ~50% higher than a carbon-loaded palladium electrocatalyst (Pd/C) in alkaline media. This confirms that the glucose electrooxidation and sensing performance of a Pd/C can be improved by the synergy of graphitic carbon nitride (C3N4), though C3N4 exhibits poor electrical conductivity. Compared to Pd/C, the size of Pd nanoparticles in Pd/C3N4-C decreases. As a result, the activity of Pd/C3N4-C is enhanced due to the higher dispersion and the synergistic effect. Pd/C3N4-C presents a rapid response and high sensitivity to glucose. The sensitivity for glucose sensing at Pd/C3N4-C is 3.3 times that of at Pd/C in the range of 0.001–10 mM. In the lower range of 0.001–1 mM, the sensitivity at Pd/C3N4-C is ~10 times greater than Pd/C. Full article
(This article belongs to the Special Issue Catalytic Properties of Nanostructured Electrodic Materials)
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Open AccessReview
Semiconductor Electrode Materials Applied in Photoelectrocatalytic Wastewater Treatment—an Overview
Catalysts 2020, 10(4), 439; https://doi.org/10.3390/catal10040439 - 18 Apr 2020
Viewed by 342
Abstract
Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable [...] Read more.
Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable raw materials. Conventional sewage treatment systems are often not efficient enough for the complete degradation of pollutants and they are characterized by high energy consumption. Moreover, the chemical energy that is stored in the wastewater is wasted. A solution to these problems is an application of photoelectrocatalytic treatment methods, especially when they are coupled with energy generation. The paper presents a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants. The fundamentals of photoelectrocatalytic reactions and the mechanism of pollutants treatment as well as parameters affecting the treatment process are presented. Examples of different semiconductor photoelectrodes that are applied in treatment processes are described in order to present the strengths and weaknesses of the photoelectrocatalytic treatment of industrial wastewater. This overview is an addition to the existing knowledge with a particular focus on the main experimental conditions employed in the photoelectrocatalytic degradation of various pollutants with the application of semiconductor photoelectrodes. Full article
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Open AccessArticle
Preparation of Ruthenium Olefin Metathesis Catalysts Immobilized on MOF, SBA-15, and 13X for Probing Heterogeneous Boomerang Effect
Catalysts 2020, 10(4), 438; https://doi.org/10.3390/catal10040438 - 17 Apr 2020
Viewed by 460
Abstract
Promoted by homogeneous Ru-benzylidene complexes, the olefin metathesis reaction is a powerful methodology for C-C double bonds formation that can find a number of applications in green chemical production. A set of heterogeneous olefin metathesis pre-catalysts composed of ammonium-tagged Ru-benzylidene complexes 4 (commercial [...] Read more.
Promoted by homogeneous Ru-benzylidene complexes, the olefin metathesis reaction is a powerful methodology for C-C double bonds formation that can find a number of applications in green chemical production. A set of heterogeneous olefin metathesis pre-catalysts composed of ammonium-tagged Ru-benzylidene complexes 4 (commercial FixCat™ catalyst) and 6 (in-house made) immobilized on solid supports such as 13X zeolite, metal-organic framework (MOF), and SBA-15 silica were obtained and tested in catalysis. These hybrid materials were doped with various amounts of ammonium-tagged styrene derivative 5—a precursor of a spare benzylidene ligand—in order to enhance pre-catalyst regeneration via the so-called release-return “boomerang effect”. Although this effect was for the first time observed inside the solid support, we discovered that non-doped systems gave better results in terms of the resulting turnover number (TON) values, and the most productive were hybrid catalysts composed of 4@MOF, 4@SBA-15, and 6@SBA-15. Full article
(This article belongs to the Special Issue SBA-15 and Catalysis)
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Open AccessFeature PaperArticle
Acid Hydrolysis of Lignocellulosic Biomass: Sugars and Furfurals Formation
Catalysts 2020, 10(4), 437; https://doi.org/10.3390/catal10040437 - 17 Apr 2020
Viewed by 340
Abstract
Hydrolysis of lignocellulosic biomass is a crucial step for the production of sugars and biobased platform chemicals. Pretreatment experiments in a semi-continuous plant with diluted sulphuric acid as catalyst were carried out to measure the time-dependent formation of sugars (glucose, xylose, mannose), furfurals, [...] Read more.
Hydrolysis of lignocellulosic biomass is a crucial step for the production of sugars and biobased platform chemicals. Pretreatment experiments in a semi-continuous plant with diluted sulphuric acid as catalyst were carried out to measure the time-dependent formation of sugars (glucose, xylose, mannose), furfurals, and organic acids (acetic, formic, and levulinic acid) at different hydrolysis temperatures (180, 200, 220 °C) of one representative of each basic type of lignocellulose: hardwood, softwood, and grass. The addition of the acid catalyst is followed by a sharp increase in the sugar concentration. Xylose and mannose were mainly formed in the initial stages of the process, while glucose was released slowly. Increasing the reaction temperature had a positive effect on the formation of furfurals and organic acids, especially on hydroxymehtylfurfural (HMF) and levulinic acid, regardless of biomass type. In addition, large amounts of formic acid were released during the hydrolysis of miscanthus grass. Structural changes in the solid residue show a complete hydrolysis of hemicellulose at 180 °C and of cellulose at 200 °C after around 120 min reaction time. The results obtained in this study can be used for the optimisation of the hydrolysis conditions and reactor design to maximise the yields of desired products, which might be sugars or furfurals. Full article
(This article belongs to the Special Issue Catalysis in Lignocellulosic Biomass Conversion)
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Open AccessArticle
Activated Carbon Supported Hafnium(IV) Chloride as an Efficient, Recyclable, and Facile Removable Catalyst for Expeditious Parallel Synthesis of Benzimidazoles
Catalysts 2020, 10(4), 436; https://doi.org/10.3390/catal10040436 - 17 Apr 2020
Viewed by 258
Abstract
A highly efficient method for parallel synthesis of a diversity of 1,2-disubstituted benzimidazoles from N-substituted phenylenediamines and aldehydes has been developed by using 10 mol% HfCl4 on activated carbon (HfCl4/C) as the catalyst. The newly reported HfCl4/C [...] Read more.
A highly efficient method for parallel synthesis of a diversity of 1,2-disubstituted benzimidazoles from N-substituted phenylenediamines and aldehydes has been developed by using 10 mol% HfCl4 on activated carbon (HfCl4/C) as the catalyst. The newly reported HfCl4/C catalyst not only mediated fast and clean formation of benzimidazoles but also could be easily removed from the reaction solution and reused up to eight times. Scanning electron microscope (SEM) and thermal desorption studies showed that activated carbon could reversibly adsorb and release Hf(IV) in ethanol upon cooling and heating, thereby serving as a thermal-controlled solid support. Full article
(This article belongs to the Special Issue Supported Metal Catalysts and Their Applications in Fine Chemicals)
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Open AccessArticle
Self-Metathesis of Methyl Oleate Using Ru-NHC Complexes: A Kinetic Study
Catalysts 2020, 10(4), 435; https://doi.org/10.3390/catal10040435 - 17 Apr 2020
Viewed by 338
Abstract
A kinetic study concerning the self-metathesis of methyl oleate and methyl elaidate was performed, using a variety of NHC-ruthenium pre-catalysts, bearing either mesityl groups or di-isopropyl-phenyl groups on the NHC ligand and various trans ligands with respect to the NHC unit. We showed [...] Read more.
A kinetic study concerning the self-metathesis of methyl oleate and methyl elaidate was performed, using a variety of NHC-ruthenium pre-catalysts, bearing either mesityl groups or di-isopropyl-phenyl groups on the NHC ligand and various trans ligands with respect to the NHC unit. We showed that the system can be satisfactorily described using one initiation constant per pre-catalyst and four propagation constants that, conversely, do not depend on the pre-catalyst. The difference of reactivity with oleate (Z) and elaidate (E) can be fully explained by the propagation parameters; the studied pre-catalysts initiate with the same rate starting from the Z or the E olefin. The ranking of the propagation parameters is driven by the thermodynamic equilibrium. The transformation rates of Z and E isomers is only driven by these propagation constants and nothing differentiates the initiation step. Full article
(This article belongs to the Special Issue N‐Heterocyclic Carbenes and Their Complexes in Catalysis)
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