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Catalysts, Volume 7, Issue 12 (December 2017)

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Editorial

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Open AccessEditorial Catalysis for Low-Temperature Fuel Cells
Catalysts 2017, 7(12), 370; doi:10.3390/catal7120370
Received: 23 November 2017 / Revised: 28 November 2017 / Accepted: 28 November 2017 / Published: 1 December 2017
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Abstract
Today, the development of active and stable catalysts still represents a challenge to be overcome in the research field of low-temperature fuel cells.[...] Full article
(This article belongs to the Special Issue Catalysis for Low Temperature Fuel Cells)

Research

Jump to: Editorial, Review

Open AccessCommunication A Novel Oxidation of Salicyl Alcohols Catalyzed by Lipase
Catalysts 2017, 7(12), 354; doi:10.3390/catal7120354
Received: 26 October 2017 / Revised: 18 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
A novel and efficient oxidation of salicyl alcohols to the corresponding salicylaldehydes catalyzed by lipase is reported for the first time. Under the optimal reaction conditions, the method exhibited high yields (81–95%) and selectivities for salicylaldehydes. Moreover, this study expands the application of
[...] Read more.
A novel and efficient oxidation of salicyl alcohols to the corresponding salicylaldehydes catalyzed by lipase is reported for the first time. Under the optimal reaction conditions, the method exhibited high yields (81–95%) and selectivities for salicylaldehydes. Moreover, this study expands the application of enzyme catalytic promiscuity in organic synthesis. Full article
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Open AccessArticle Catalytic Activities of Ribozymes and DNAzymes in Water and Mixed Aqueous Media
Catalysts 2017, 7(12), 355; doi:10.3390/catal7120355
Received: 1 November 2017 / Revised: 13 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
Catalytic nucleic acids are regarded as potential therapeutic agents and biosensors. The catalytic activities of nucleic acid enzymes are usually investigated in dilute aqueous solutions, although the physical properties of the reaction environment inside living cells and that in the area proximal to
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Catalytic nucleic acids are regarded as potential therapeutic agents and biosensors. The catalytic activities of nucleic acid enzymes are usually investigated in dilute aqueous solutions, although the physical properties of the reaction environment inside living cells and that in the area proximal to the surface of biosensors in which they operate are quite different from those of pure water. The effect of the molecular environment is also an important focus of research aimed at improving and expanding nucleic acid function by addition of organic solvents to aqueous solutions. In this study, the catalytic activities of RNA and DNA enzymes (hammerhead ribozyme, 17E DNAzyme, R3C ribozyme, and 9DB1 DNAzyme) were investigated using 21 different mixed aqueous solutions comprising organic compounds. Kinetic measurements indicated that these enzymes can display enhanced catalytic activity in mixed solutions with respect to the solution containing no organic additives. Correlation analyses revealed that the turnover rate of the reaction catalyzed by hammerhead ribozyme increased in a medium with a lower dielectric constant than water, and the turnover rate of the reaction catalyzed by 17E DNAzyme increased in conditions that increased the strength of DNA interactions. On the other hand, R3C ribozyme and 9DB1 DNAzyme displayed no significant turnover activity, but their single-turnover rates increased in many mixed solutions. Our data provide insight into the activity of catalytic nucleic acids under various conditions that are applicable to the medical and technology fields, such as in living cells and in biosensors. Full article
(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)
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Open AccessArticle Catalytic Pyrolysis of Chilean Oak: Influence of Brønsted Acid Sites of Chilean Natural Zeolite
Catalysts 2017, 7(12), 356; doi:10.3390/catal7120356
Received: 2 November 2017 / Revised: 20 November 2017 / Accepted: 21 November 2017 / Published: 24 November 2017
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Abstract
This paper proposes the Chilean natural zeolite as catalyst on bio-oil upgrade processes. The aim of this study was to analyze chemical composition of bio-oil samples obtained from catalytic pyrolysis of Chilean native oak in order to increase bio-oil stability during storage. In
[...] Read more.
This paper proposes the Chilean natural zeolite as catalyst on bio-oil upgrade processes. The aim of this study was to analyze chemical composition of bio-oil samples obtained from catalytic pyrolysis of Chilean native oak in order to increase bio-oil stability during storage. In order to identify chemical compounds before and after storage, biomass pyrolysis was carried out in a fixed bed reactor at 623 K and bio-oil samples were characterized by gas chromatography/mass spectrophotometry (GC/MS). A bio-oil fractionation method was successfully applied here. Results indicate that bio-oil viscosity decreases due to active sites on the zeolite framework. Active acids sites were associated with an increment of alcohols, aldehydes, and hydrocarbon content during storage. Higher composition on aldehydes and alcohols after storage could be attributed to the occurrence of carbonyl reduction reactions that promotes them. These reactions are influenced by zeolite surface characteristics and could be achieved via the direct contribution of Brønsted acid sites to Chilean natural zeolite. Full article
(This article belongs to the Special Issue Catalytic Processes for The Valorisation of Biomass Derived Molecules)
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Open AccessFeature PaperArticle Using Density Functional Theory to Model Realistic TiO2 Nanoparticles, Their Photoactivation and Interaction with Water
Catalysts 2017, 7(12), 357; doi:10.3390/catal7120357
Received: 16 October 2017 / Revised: 8 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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Abstract
Computational modeling of titanium dioxide nanoparticles of realistic size is extremely relevant for the direct comparison with experiments but it is also a rather demanding task. We have recently worked on a multistep/scale procedure to obtain global optimized minimum structures for chemically stable
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Computational modeling of titanium dioxide nanoparticles of realistic size is extremely relevant for the direct comparison with experiments but it is also a rather demanding task. We have recently worked on a multistep/scale procedure to obtain global optimized minimum structures for chemically stable spherical titania nanoparticles of increasing size, with diameter from 1.5 nm (~300 atoms) to 4.4 nm (~4000 atoms). We use first self-consistent-charge density functional tight-binding (SCC-DFTB) methodology to perform thermal annealing simulations to obtain globally optimized structures and then hybrid density functional theory (DFT) to refine them and to achieve high accuracy in the description of structural and electronic properties. This allows also to assess SCC-DFTB performance in comparison with DFT(B3LYP) results. As a further step, we investigate photoexcitation and photoemission processes involving electron/hole pair formation, separation, trapping and recombination in the nanosphere of medium size by hybrid DFT. Finally, we show how a recently defined new set of parameters for SCC-DFTB allows for a proper description of titania/water multilayers interface, which paves the way for modeling large realistic nanoparticles in aqueous environment. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessArticle Process Intensification of Alkynol Semihydrogenation in a Tube Reactor Coated with a Pd/ZnO Catalyst
Catalysts 2017, 7(12), 358; doi:10.3390/catal7120358
Received: 26 October 2017 / Revised: 16 November 2017 / Accepted: 20 November 2017 / Published: 25 November 2017
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Abstract
Semihydrogenation of 2-methyl-3-butyn-2-ol (MBY) was studied in a 5 m tube reactor wall-coated with a 5 wt% Pd/ZnO catalyst. The system allowed for the excellent selectivity towards the intermediate alkene of 97.8 ± 0.2% at an ambient H2 pressure and a MBY
[...] Read more.
Semihydrogenation of 2-methyl-3-butyn-2-ol (MBY) was studied in a 5 m tube reactor wall-coated with a 5 wt% Pd/ZnO catalyst. The system allowed for the excellent selectivity towards the intermediate alkene of 97.8 ± 0.2% at an ambient H2 pressure and a MBY conversion below 90%. The maximum alkene yield reached 94.6% under solvent-free conditions and 96.0% in a 30 vol % MBY aqueous solution. The reactor stability was studied for 80 h on stream with a deactivation rate of only 0.07% per hour. Such a low deactivation rate provides a continuous operation of one month with only a two-fold decrease in catalyst activity and a metal leaching below 1 parts per billion (ppb). The excellent turn-over numbers (TON) of above 105 illustrates a very efficient utilisation of the noble metal inside catalyst-coated tube reactors. When compared to batch operation at 70 °C, the reaction rate in flow reactor can be increased by eight times at a higher reaction temperature, keeping the same product decomposition of about 1% in both cases. Full article
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Open AccessArticle Approaching Immobilization of Enzymes onto Open Porous Basotect®
Catalysts 2017, 7(12), 359; doi:10.3390/catal7120359
Received: 17 October 2017 / Revised: 14 November 2017 / Accepted: 16 November 2017 / Published: 27 November 2017
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Abstract
For the first time, commercial macroporous melamine formaldehyde foam Basotect® (BT) was used as a basic carrier material for both adsorptive and covalent enzyme immobilization. In order to access inherent amino groups, the Basotect® surface was pretreated with hydrochloric acid. The
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For the first time, commercial macroporous melamine formaldehyde foam Basotect® (BT) was used as a basic carrier material for both adsorptive and covalent enzyme immobilization. In order to access inherent amino groups, the Basotect® surface was pretreated with hydrochloric acid. The resulting material revealed 6 nmol of superficial amino groups per milligram Basotect®. Different optimized strategies for tethering the laccase from Trametes versicolor and the lipase from Thermomyces lanuginosus onto the pre-treated Basotect® surface were studied. Particularly, for covalent immobilization, two different strategies were pursued: lipase was tethered via a cross-linking method using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and laccase was bound after functionalizing Basotect® with hydrophilic copolymer poly(ethylene-alt-maleic anhydride) (PEMA). Prior to laccase immobilization, the PEMA coating of Basotect® was verified by ATR-FTIR analysis. Subsequent quantification of available high-reactive PEMA anhydride moieties revealed an amount of 1028 ± 73 nmol per mg Basotect®. The surface-bound enzyme amounts were quantified as 4.1–5.8 μg per mg Basotect®. A theoretical surface-covered enzyme mass for the ideal case that an enzyme monolayer was immobilized onto the Basotect® surface was calculated and compared to the amount of adsorptive and covalently bound enzymes before and after treatment with SDS. Furthermore, the enzyme activities were determined for the different immobilization approaches, and the stability during storage over time and against sodium dodecyl sulfate treatment was monitored. Additionally, PEMA-BT-bound laccase was tested for the elimination of anthropogenic micropollutant bisphenol A from contaminated water in a cost-effective and environmentally-friendly way and resulted in a degradation rate higher than 80%. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessArticle Design and Application of Magnetic Photocatalysts for Water Treatment. The Effect of Particle Charge on Surface Functionality
Catalysts 2017, 7(12), 360; doi:10.3390/catal7120360
Received: 6 October 2017 / Revised: 30 October 2017 / Accepted: 21 November 2017 / Published: 27 November 2017
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Abstract
Core-interlayer-shell Fe3O4/SiO2/TiO2, CoFe2O4/SiO2/TiO2 and BaFe12O19/SiO2/TiO2 magnetic photocatalysts were obtained. A water-in-oil microemulsion system with suitable surfactants was used for functionalization of
[...] Read more.
Core-interlayer-shell Fe3O4/SiO2/TiO2, CoFe2O4/SiO2/TiO2 and BaFe12O19/SiO2/TiO2 magnetic photocatalysts were obtained. A water-in-oil microemulsion system with suitable surfactants was used for functionalization of the magnetic core with silica interlayer and TiO2-based photocatalyst. Uncoated and coated particles were characterized by electrophoretic measurements, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (BET) measurements, diffuse reflectance spectroscopy (DRS) and vibrating sample magnetometer (VSM) analysis. The pH of the solution and corresponding zeta potential was found to be essential for appropriate formation of ferrite core/silica interlayer/TiO2 shell nanocomposite, since the electrical charge controls interactions during functionalization of the magnetic core particles. Thus, the development of multilayer structure in the isoelectric point (IEP) region enhanced adhesion of ferrite, silica and titania particles. The obtained Fe3O4/SiO2/TiO2, CoFe2O4/SiO2/TiO2 and BaFe12O19/SiO2/TiO2 nanocomposites revealed superparamagnetic behavior. The decomposition rate of phenol and carbamazepine allowed to estimate their photocatalytic activity. Progress of photocatalytic mineralization of organic compounds was evaluated by total organic carbon (TOC) measurements. Photocatalytic activity measured in four subsequent cycles showed good reusability as no loss of efficiency of phenol degradation was observed. Full article
(This article belongs to the Special Issue Magnetic Nanocatalysts)
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Open AccessFeature PaperArticle Stereoselective Copolymerization of Styrene with Terpenes Catalyzed by an Ansa-Lanthanidocene Catalyst: Access to New Syndiotactic Polystyrene-Based Materials
Catalysts 2017, 7(12), 361; doi:10.3390/catal7120361
Received: 3 November 2017 / Revised: 24 November 2017 / Accepted: 25 November 2017 / Published: 27 November 2017
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Abstract
The copolymerization of bio-renewable β-myrcene or β-farnesene with styrene was examined using an ansa-neodymocene catalyst, affording two series of copolymers with high styrene content and unprecedented syndioregularity of the polystyrene sequences. The incorporation of terpene in the copolymers ranged from
[...] Read more.
The copolymerization of bio-renewable β-myrcene or β-farnesene with styrene was examined using an ansa-neodymocene catalyst, affording two series of copolymers with high styrene content and unprecedented syndioregularity of the polystyrene sequences. The incorporation of terpene in the copolymers ranged from 5.6 to 30.8 mol % (β-myrcene) and from 2.5 to 9.8 mol % (β-farnesene), respectively. NMR spectroscopy and DSC analyses suggested that the microstructure of the copolymers consists of 1,4- and 3,4-poly(terpene) units randomly distributed along syndiotactic polystyrene chains. The thermal properties of the copolymers are strongly dependent on the terpene content, which is easily controlled by the initial feed. The terpolymerization of styrene with β-myrcene in the presence of ethylene was also examined. Full article
(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)
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Open AccessArticle Saturated Resin Ectopic Regeneration by Non-Thermal Dielectric Barrier Discharge Plasma
Catalysts 2017, 7(12), 362; doi:10.3390/catal7120362
Received: 26 October 2017 / Revised: 21 November 2017 / Accepted: 22 November 2017 / Published: 27 November 2017
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Abstract
Textile dyes are some of the most refractory organic compounds in the environment due to their complex and various structure. An integrated resin adsorption/Dielectric Barrier Discharge (DBD) plasma regeneration was proposed to treat the indigo carmine solution. It is the first time to
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Textile dyes are some of the most refractory organic compounds in the environment due to their complex and various structure. An integrated resin adsorption/Dielectric Barrier Discharge (DBD) plasma regeneration was proposed to treat the indigo carmine solution. It is the first time to report ectopic regeneration of the saturated resins by non-thermal Dielectric Barrier Discharge. The adsorption/desorption efficiency, surface functional groups, structural properties, regeneration efficiency, and the intermediate products between gas and liquid phase before and after treatment were investigated. The results showed that DBD plasma could maintain the efficient adsorption performance of resins while degrading the indigo carmine adsorbed by resins. The degradation rate of indigo carmine reached 88% and the regeneration efficiency (RE) can be maintained above 85% after multi-successive regeneration cycles. The indigo carmine contaminants were decomposed by a variety of reactive radicals leading to fracture of exocyclic C=C bond, which could cause decoloration of dye solution. Based on above results, a possible degradation pathway for the indigo carmine by resin adsorption/DBD plasma treatment was proposed. Full article
(This article belongs to the Special Issue Photocatalysts for Organics Degradation)
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Open AccessArticle Racemization of Serine Residues Catalyzed by Dihydrogen Phosphate Ion: A Computational Study
Catalysts 2017, 7(12), 363; doi:10.3390/catal7120363
Received: 26 October 2017 / Revised: 16 November 2017 / Accepted: 22 November 2017 / Published: 27 November 2017
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Abstract
Spontaneous, nonenzymatic reactions in proteins are known to have relevance to aging and age-related diseases, such as cataract and Alzheimer’s disease. Among such reactions is the racemization of Ser residues, but its mechanism in vivo remains to be clarified. The most likely intermediate
[...] Read more.
Spontaneous, nonenzymatic reactions in proteins are known to have relevance to aging and age-related diseases, such as cataract and Alzheimer’s disease. Among such reactions is the racemization of Ser residues, but its mechanism in vivo remains to be clarified. The most likely intermediate is an enol. Although being nonenzymatic, the enolization would need to be catalyzed to occur at a biologically relevant rate. In the present study, we computationally found plausible reaction pathways for the enolization of a Ser residue where a dihydrogen phosphate ion, H2PO4, acts as a catalyst. The H2PO4 ion mediates the proton transfer required for the enolization by acting simultaneously as both a general base and a general acid. Using the B3LYP density functional theory method, reaction pathways were located in the gas phase and hydration effects were evaluated by single-point calculations using the SM8 continuum model. The activation barriers calculated for the reaction pathways found were around 100 kJ mol−1, which is consistent with spontaneous reactions occurring at physiological temperature. Our results are also consistent with experimental observations that Ser residue racemization occurs more readily in flexible regions in proteins. Full article
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Open AccessArticle A Novel Metal–Organic Framework Route to Embed Co Nanoparticles into Multi-Walled Carbon Nanotubes for Effective Oxygen Reduction in Alkaline Media
Catalysts 2017, 7(12), 364; doi:10.3390/catal7120364
Received: 1 November 2017 / Revised: 22 November 2017 / Accepted: 23 November 2017 / Published: 27 November 2017
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Abstract
Metal–organic framework (MOF) materials can be used as precursors to prepare non-precious metal catalysts (NPMCs) for oxygen reduction reaction (ORR). Herein, we prepared a novel MOF material (denoted as Co-bpdc) and then combined it with multi-walled carbon nanotubes (MWCNTs) to form Co-bpdc/MWCNTs composites.
[...] Read more.
Metal–organic framework (MOF) materials can be used as precursors to prepare non-precious metal catalysts (NPMCs) for oxygen reduction reaction (ORR). Herein, we prepared a novel MOF material (denoted as Co-bpdc) and then combined it with multi-walled carbon nanotubes (MWCNTs) to form Co-bpdc/MWCNTs composites. After calcination, the cobalt ions from Co-bpdc were converted into Co nanoparticles, which were distributed in the graphite carbon layers and MWCNTs to form Co-bpdc/MWCNTs. The prepared catalysts were characterized by TEM (Transmission electron microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), BET (Brunauer–Emmett–Teller), and Raman spectroscopy. The electrocatalytic activity was measured by using rotating disk electrode (RDE) voltammetry. The catalysts showed higher ORR catalytic activity than the commercial Pt/C catalyst in alkaline solution. Co-bpdc/MWCNTs-100 showed the highest ORR catalytic activity, with an initial reduction potential and half-wave potential reaching 0.99 V and 0.92 V, respectively. The prepared catalysts also showed superior stability and followed the 4-electron pathway ORR process in alkaline solution. Full article
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Open AccessFeature PaperArticle Ene-yne Cross-Metathesis for the Preparation of 2,3-Diaryl-1,3-dienes
Catalysts 2017, 7(12), 365; doi:10.3390/catal7120365
Received: 10 November 2017 / Revised: 20 November 2017 / Accepted: 21 November 2017 / Published: 27 November 2017
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Abstract
Ene-yne cross-metathesis from alkynes and ethylene is a useful method to produce substituted conjugated butadiene derivatives. If this method has been used with aliphatic alkynes, it has however never been used starting from diarylacetylenes as internal alkynes. We show that the ene-yne cross-metathesis
[...] Read more.
Ene-yne cross-metathesis from alkynes and ethylene is a useful method to produce substituted conjugated butadiene derivatives. If this method has been used with aliphatic alkynes, it has however never been used starting from diarylacetylenes as internal alkynes. We show that the ene-yne cross-metathesis catalyzed by the second generation Hoveyda ruthenium catalyst provides the 2,3-diarylbuta-1,3-dienes under 3 atm of ethylene at 100 °C. The scope and limitations of the reaction have been evaluated starting from unsymmetrical functionalized diarylacetylene derivatives hence leading to unsymmetrical 2,3-diarylbuta-1,3-dienes in a straightforward and environmentally acceptable manner. Full article
(This article belongs to the Special Issue Catalysis of Olefin Metathesis)
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Open AccessArticle Engineering Pyrite-Type Bimetallic Ni-Doped CoS2 Nanoneedle Arrays over a Wide Compositional Range for Enhanced Oxygen and Hydrogen Electrocatalysis with Flexible Property
Catalysts 2017, 7(12), 366; doi:10.3390/catal7120366
Received: 12 November 2017 / Revised: 23 November 2017 / Accepted: 23 November 2017 / Published: 27 November 2017
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Abstract
The development of cheap and efficient catalytic electrodes is of great importance, to promote the sluggish overall water-splitting systems associated with the large-scale application of clean and renewable energy technologies. In this work, we report the controlled synthesis of pyrite-type bimetallic Ni-doped CoS
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The development of cheap and efficient catalytic electrodes is of great importance, to promote the sluggish overall water-splitting systems associated with the large-scale application of clean and renewable energy technologies. In this work, we report the controlled synthesis of pyrite-type bimetallic Ni-doped CoS2 nanoneedle (NN) arrays supported on stainless steel (SS) (designated as NixCo1xS2 NN/SS, 0 ≤ x ≤ 1) and the related compositional influence on electrocatalytic efficiencies for the oxygen and hydrogen evolution reaction (OER/HER). Impressively, the Ni0.33Co0.67S2 NN/SS displays superior activity and faster kinetics for catalyzing OER (low overpotential of 286 mV at 50 mA cm−2; Tafel value of 55 mV dec−1) and HER (low overpotential of 350 mV at 30 mA cm−2; Tafel value of 76 mV dec−1) than those of counterparts with other Ni/Co ratios and also monometallic Ni- or Co-based sulfides, which is attributed to the optimized balance from the improved electron transfer capability, increased exposure of electrocatalytic active sites, and favorable dissipation of gaseous products over the nanoneedle surface. Furthermore, the conductive, flexible SS support and firmly attached in-situ integrated feature, result in the flexibility and remarkable long-term stability of as-prepared binder-free Ni0.33Co0.67S2 NN/SS electrode. These results demonstrate element-doping could be an efficient route at the atomic level to design new materials and further optimize the surface physicochemical properties for enhancing the overall electrochemical water splitting activity. Full article
(This article belongs to the Special Issue Nanostructured Materials for Applications in Heterogeneous Catalysis)
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Open AccessCommunication Development of Highly Nano-Dispersed NiO/GDC Catalysts from Ion Exchange Resin Templates
Catalysts 2017, 7(12), 368; doi:10.3390/catal7120368
Received: 7 November 2017 / Revised: 20 November 2017 / Accepted: 20 November 2017 / Published: 28 November 2017
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Abstract
Novel NiO/GDC (Gadolinium-doped Ceria) cermet catalysts were developed by the Weak Acid Resin (WAR) method using an ion exchange resin template. In addition, the specific surface area of these tunable materials was enhanced by NiO partial dissolution in aqueous acid solution. The whole
[...] Read more.
Novel NiO/GDC (Gadolinium-doped Ceria) cermet catalysts were developed by the Weak Acid Resin (WAR) method using an ion exchange resin template. In addition, the specific surface area of these tunable materials was enhanced by NiO partial dissolution in aqueous acid solution. The whole procedure highly improved the micro-structural properties of these materials compared to previous studies. Catalysts with high metal loadings (≥10%), small Ni nanoparticles (<10 nm), and high specific surface areas (>70 m2/g) were achieved. These properties are promising for catalytic applications such as methane steam reforming for H2 production. Full article
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Open AccessFeature PaperArticle Synthesis, Structure and 1,3-Butadiene Polymerization Behavior of Vanadium(III) Phosphine Complexes
Catalysts 2017, 7(12), 369; doi:10.3390/catal7120369
Received: 9 November 2017 / Revised: 24 November 2017 / Accepted: 25 November 2017 / Published: 28 November 2017
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Abstract
A series of vanadium(III) complexes bearing monodentate tertiary phosphine ligands of the type VCl3(PRnPh3-n)2 (n = 0 (1a); n = 1 and R = Me (1b), Et (1c),
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A series of vanadium(III) complexes bearing monodentate tertiary phosphine ligands of the type VCl3(PRnPh3-n)2 (n = 0 (1a); n = 1 and R = Me (1b), Et (1c), iPr (1d), Cy (1e); n = 2 and R = Me (1f), Et (1g), Cy (1h)), and VCl3(PR3)2 (R = Cyp (2a), Cy (2b), nPr (2c), tBu (2d)) were synthesized and characterized. In the case of 1c, 1g and 2a single crystals were also obtained and their molecular structures were determined. All the complexes were used, in combination with methylaluminoxane (sMAO) or AlMe3–free MAO (dMAO), for the polymerization of 1,3-butadiene, exhibiting rather good activity and giving polymers with different microstructure depending on the nature of the phosphine ligand and the type of co-catalyst employed. Full article
(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)
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Open AccessArticle Enhanced Photodegradation Activity of Hydrogen-Terminated Si Nanowires Arrays with Different-Oriented Crystal Phases
Catalysts 2017, 7(12), 371; doi:10.3390/catal7120371
Received: 14 October 2017 / Revised: 22 November 2017 / Accepted: 25 November 2017 / Published: 1 December 2017
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Abstract
Although Si nanowires (NWs) arrays are superior candidates for visible light photocatalysis, reports about the photodegradation activity of various crystal-orientated Si NWs are still insufficient. Here, light-doped hydrogen-terminated Si NWs arrays with different crystal orientations were prepared via a metal-assisted chemical etching method
[...] Read more.
Although Si nanowires (NWs) arrays are superior candidates for visible light photocatalysis, reports about the photodegradation activity of various crystal-orientated Si NWs are still insufficient. Here, light-doped hydrogen-terminated Si NWs arrays with different crystal orientations were prepared via a metal-assisted chemical etching method (MACE), which simply modulated the concentration of the oxidizer, H2O2. Their dye photodegradation activities were systematically and comprehensively investigated. When compared with Si NWs arrays with crystal orientations of (110) and (111), Si NWs arrays with (100) crystal orientation exhibit a superior photodegradation activity and stability due to the anisotropy of optical and physical properties. The n-type Si NWs arrays exhibit better photodegradation activity than the p-type Si NWs arrays of the same crystal orientation and similar length. The results provide a further understanding of the synthesis of Si NWs arrays with various orientations, and the relationships between photodegradation activity/stability and crystal orientations. Full article
(This article belongs to the Special Issue Nanostructured Materials for Applications in Heterogeneous Catalysis)
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Open AccessArticle Influence of the Nanostructure of Gallium Oxide Catalysts on Conversion in the Green Synthesis of Carbamates
Catalysts 2017, 7(12), 372; doi:10.3390/catal7120372
Received: 17 October 2017 / Revised: 22 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
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Abstract
The nanostructure of β-gallium oxide crystals influences the conversion to carbamates; specifically, for the synthesis of alkyl carbamates (like propyl N-octylcarbamate) from CO2 and n-propanol in the absence of phosgene. The nanostructures with variable aspect ratios (length (L)/width (D); from 2 to
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The nanostructure of β-gallium oxide crystals influences the conversion to carbamates; specifically, for the synthesis of alkyl carbamates (like propyl N-octylcarbamate) from CO2 and n-propanol in the absence of phosgene. The nanostructures with variable aspect ratios (length (L)/width (D); from 2 to 18) were prepared by the controlled addition of neutral and cationic surfactants during gallium oxide synthesis. These catalysts displayed selectivities to the corresponding carbamates as high as ~70%, superior to non-nanostructured Ga2O3 catalysts. The conversion was found to be inversely proportional to the square of the relative crystallinity. The catalysts retained their structure and catalytic performance upon recycling. Full article
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Open AccessArticle Immobilization of Cellulase on a Functional Inorganic–Organic Hybrid Support: Stability and Kinetic Study
Catalysts 2017, 7(12), 374; doi:10.3390/catal7120374
Received: 7 November 2017 / Revised: 28 November 2017 / Accepted: 29 November 2017 / Published: 1 December 2017
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Abstract
Cellulase from Aspergillus niger was immobilized on a synthesized TiO2–lignin hybrid support. The enzyme was effectively deposited on the inorganic–organic hybrid matrix, mainly via physical interactions. The optimal initial immobilization parameters, selected for the highest relative activity, were pH 5.0, 6
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Cellulase from Aspergillus niger was immobilized on a synthesized TiO2–lignin hybrid support. The enzyme was effectively deposited on the inorganic–organic hybrid matrix, mainly via physical interactions. The optimal initial immobilization parameters, selected for the highest relative activity, were pH 5.0, 6 h process duration, and an enzyme solution concentration of 5 mg/mL. Moreover, the effects of pH, temperature, and number of consecutive catalytic cycles and the storage stability of free and immobilized cellulase were evaluated and compared. Thermal and chemical stability were significantly improved, while after 3 h at a temperature of 50 °C and pH 6.0, the immobilized cellulase retained over 80% of its initial activity. In addition, the half-life of the immobilized cellulase (307 min) was five times that of the free enzyme (63 min). After ten repeated catalytic cycles, the immobilized biocatalyst retained over 90% of its initial catalytic properties. This study presents a protocol for the production of highly stable and reusable biocatalytic systems for practical application in the hydrolysis of cellulose. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessArticle Cross-Linked CoMoO4/rGO Nanosheets as Oxygen Reduction Catalyst
Catalysts 2017, 7(12), 375; doi:10.3390/catal7120375
Received: 23 November 2017 / Accepted: 28 November 2017 / Published: 4 December 2017
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Abstract
Development of inexpensive and robust electrocatalysts towards oxygen reduction reaction (ORR) is crucial for the cost-affordable manufacturing of metal-air batteries and fuel cells. Here we show that cross-linked CoMoO4 nanosheets and reduced graphene oxide (CoMoO4/rGO) can be integrated in a
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Development of inexpensive and robust electrocatalysts towards oxygen reduction reaction (ORR) is crucial for the cost-affordable manufacturing of metal-air batteries and fuel cells. Here we show that cross-linked CoMoO4 nanosheets and reduced graphene oxide (CoMoO4/rGO) can be integrated in a hybrid material under one-pot hydrothermal conditions, yielding a composite material with promising catalytic activity for oxygen reduction reaction (ORR). Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to investigate the efficiency of the fabricated CoMoO4/rGO catalyst towards ORR in alkaline conditions. The CoMoO4/rGO composite revealed the main reduction peak and onset potential centered at 0.78 and 0.89 V (vs. RHE), respectively. This study shows that the CoMoO4/rGO composite is a highly promising catalyst for the ORR under alkaline conditions, and potential noble metal replacement cathode in fuel cells and metal-air batteries. Full article
(This article belongs to the Special Issue Recent Advances in Polyoxometalate-Catalyzed Reactions)
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Open AccessArticle Low-Temperature Sol-Gel Synthesis of Nitrogen-Doped Anatase/Brookite Biphasic Nanoparticles with High Surface Area and Visible-Light Performance
Catalysts 2017, 7(12), 376; doi:10.3390/catal7120376
Received: 21 October 2017 / Revised: 26 November 2017 / Accepted: 30 November 2017 / Published: 4 December 2017
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Abstract
Nitrogen doping in combination with the brookite phase or a mixture of TiO2 polymorphs nanomaterials can enhance photocatalytic activity under visible light. Generally, nitrogen-dopedanatase/brookite mixed phases TiO2 nanoparticles obtained by hydrothermal or solvothermal method need to be at high temperature and
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Nitrogen doping in combination with the brookite phase or a mixture of TiO2 polymorphs nanomaterials can enhance photocatalytic activity under visible light. Generally, nitrogen-dopedanatase/brookite mixed phases TiO2 nanoparticles obtained by hydrothermal or solvothermal method need to be at high temperature and with long time heating treatment. Furthermore, the surface areas of them are low (<125 m2/g). There is hardly a report on the simple and direct preparation of N-doped anatase/brookite mixed phase TiO2 nanostructures using sol-gel method at low heating temperature. In this paper, the nitrogen-doped anatase/brookite biphasic nanoparticles with large surface area (240 m2/g) were successfully prepared using sol-gel method at low temperature (165 °C), and with short heating time (4 h) under autogenous pressure. The obtained sample without subsequent annealing at elevated temperatures showed enhanced photocatalytic efficiency for the degradation of methyl orange (MO) with 4.2-, 9.6-, and 7.5-fold visible light activities compared to P25 and the amorphous samples heated in muffle furnace with air or in tube furnace with a flow of nitrogen at 165 °C, respectively. This result was attributed to the synergistic effects of nitrogen doping, mixed crystalline phases, and high surface area. Full article
(This article belongs to the Special Issue Photocatalysts for Organics Degradation)
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Open AccessCommunication Low-Dimensional ReS2/C Composite as Effective Hydrodesulfurization Catalyst
Catalysts 2017, 7(12), 377; doi:10.3390/catal7120377
Received: 30 October 2017 / Revised: 29 November 2017 / Accepted: 29 November 2017 / Published: 5 December 2017
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Abstract
Single-layer, ultrasmall ReS2 nanoplates embedded in amorphous carbon were synthesized from a hydrothermal treatment involving ammonium perrhenate, thiourea, tetraoctylammonium bromide, and further annealing. The rhenium disulfide, obtained as a low dimensional carbon composite (ReS2/C), was tested in the hydrodesulfurization of
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Single-layer, ultrasmall ReS2 nanoplates embedded in amorphous carbon were synthesized from a hydrothermal treatment involving ammonium perrhenate, thiourea, tetraoctylammonium bromide, and further annealing. The rhenium disulfide, obtained as a low dimensional carbon composite (ReS2/C), was tested in the hydrodesulfurization of light hydrocarbons, using 3-methylthiophene as the model molecule, and showed enhanced catalytic activity in comparison with a sulfide CoMo/γ-Al2O3 catalyst. The ReS2/C composite was characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption–desorption isotherms, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The improved catalytic performance of this ReS2/C composite may be ascribed to the presence of a non-stoichiometric sulfur species (ReS2−x), the absence of stacking along the c-axis, and the ultra-small basal planes, which offer a higher proportion of structural sulfur defects at the edge of the layers, known as a critical parameter for hydrodesulfurization catalytic processes. Full article
(This article belongs to the Special Issue Nanostructured Materials for Applications in Heterogeneous Catalysis)
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Open AccessArticle Preparation of Ag4Bi2O5/MnO2 Corn/Cob Like Nano Material as a Superior Catalyst for Oxygen Reduction Reaction in Alkaline Solution
Catalysts 2017, 7(12), 379; doi:10.3390/catal7120379
Received: 21 October 2017 / Revised: 30 November 2017 / Accepted: 30 November 2017 / Published: 6 December 2017
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Abstract
Ag4Bi2O5/MnO2 nano-sized material was synthesized by a co-precipitation method in concentrated KOH solution. The morphology characterization indicates that MnO2 nanoparticles with a size of 20 nm are precipitated on the surface of nano Ag4
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Ag4Bi2O5/MnO2 nano-sized material was synthesized by a co-precipitation method in concentrated KOH solution. The morphology characterization indicates that MnO2 nanoparticles with a size of 20 nm are precipitated on the surface of nano Ag4Bi2O5, forming a structure like corn on the cob. The obtained material with 60% Mn offers slightly higher initial potential (0.098 V vs. Hg/HgO) and limiting current density (−5.67 mA cm−2) at a rotating speed of 1600 rpm compared to commercial Pt/C (−0.047 V and −5.35 mA cm−2, respectively). Furthermore, the obtained material exhibits superior long-term durability and stronger methanol tolerance than commercial Pt/C. The remarkable features suggest that the Ag4Bi2O5/MnO2 nano-material is a very promising oxygen reduction reaction catalyst. Full article
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Open AccessArticle Novel Allyl Cobalt Phosphine Complexes: Synthesis, Characterization and Behavior in the Polymerization of Allene and 1,3-Dienes
Catalysts 2017, 7(12), 381; doi:10.3390/catal7120381
Received: 16 November 2017 / Revised: 1 December 2017 / Accepted: 1 December 2017 / Published: 7 December 2017
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Abstract
Novel allyl cobalt complexes, i.e., (η3-C4H7)(η4-C4H6)Co(PCyPh2) (1), (η3-C4H7)(η4-C4H6)Co(PMePh2) (2) and (η
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Novel allyl cobalt complexes, i.e., (η3-C4H7)(η4-C4H6)Co(PCyPh2) (1), (η3-C4H7)(η4-C4H6)Co(PMePh2) (2) and (η3-C5H9)(η4-C5H8)Co(PMePh2) (3), were synthesized by reacting CoCl2(PRPh2)2 (R = methyl, cyclohexyl) with 1,3-butadiene or isoprene in presence of metallic zinc. The complexes were fully characterized by Nuclear Magnetic Resonance (NMR) spectroscopy (1H and 2D experiments); in case of 1, single crystals, suitable for X-ray analysis, were obtained and the molecular structure was determined. The allyl cobalt phosphine complexes alone gave highly crystalline 1,2 polymers from 1,2-propadiene, but they did not polymerize 1,3-dienes. Nevertheless, in the presence of a stoichiometric amount of methylaluminoxane (MAO), they were able to polymerize 1,3-butadiene and substituted 1,3-butadienes such as isoprene, (E)-1,3-pentadiene, (E)-1,3-hexadiene, and (E)-3-methyl-1,3-pentadiene. Specifically, 1/MAO gave predominantly syndiotactic 1,2 polymers from 1,3-butadiene and terminally substituted 1,3-butadienes (e.g., 1,3-pentadiene and 1,3-hexadiene), but it was practically not active in the polymerization of internally substituted 1,3-butadienes (e.g., isoprene and 3-methyl-1,3-pentadiene); 2/MAO and 3/MAO exhibited instead an opposite behavior, giving predominantly isotactic 1,2 polymers from 3-methyl-1,3-pentadiene, and showing very low activity in the polymerization of 1,3-butadiene, 1,3-pentadiene and 1,3-hexadiene. The results obtained are interesting from the mechanistic point of view, and some hypotheses to explain this particular behavior were formulated. Full article
(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)
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Open AccessArticle Effects of Preparation Method on the Structure and Catalytic Activity of Ag–Fe2O3 Catalysts Derived from MOFs
Catalysts 2017, 7(12), 382; doi:10.3390/catal7120382
Received: 30 October 2017 / Revised: 4 December 2017 / Accepted: 5 December 2017 / Published: 9 December 2017
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Abstract
In this work, Ag–Fe2O3 catalysts were successfully prepared using several different methods. Our main intention was to investigate the effect of the preparation methods on the catalysts’ structure and their catalytic performance for CO oxidation. The catalysts were characterized by
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In this work, Ag–Fe2O3 catalysts were successfully prepared using several different methods. Our main intention was to investigate the effect of the preparation methods on the catalysts’ structure and their catalytic performance for CO oxidation. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), H2-temperature program reduction (H2-TPR) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Ag–Fe catalysts prepared by impregnating Ag into MIL-100 (Fe) presented the best catalytic activity, over which CO could be completely oxidized at 160 °C. Based on the characterization, it was found that more metallic Ag species and porosity existed on Ag–Fe catalysts, which could efficiently absorb atmospheric oxygen and, thus, enhance the CO oxidation. Full article
(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)
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Open AccessArticle Hydrodeoxygenation of Methyl Laurate over Ni Catalysts Supported on Hierarchical HZSM-5 Zeolite
Catalysts 2017, 7(12), 383; doi:10.3390/catal7120383
Received: 30 September 2017 / Revised: 25 November 2017 / Accepted: 30 November 2017 / Published: 11 December 2017
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Abstract
The hierarchical HZSM-5 zeolite was prepared successfully by a simple NaOH treatment method. The concentration of NaOH solution was carefully tuned to optimal the zeolite acidity and pore structure. Under NaOH treatment conditions, a large number of mesopores, which interconnected with the retained
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The hierarchical HZSM-5 zeolite was prepared successfully by a simple NaOH treatment method. The concentration of NaOH solution was carefully tuned to optimal the zeolite acidity and pore structure. Under NaOH treatment conditions, a large number of mesopores, which interconnected with the retained micropores, were created to facilitate mass transfer performance. There are very good correlations between the decline of the relative zeolite crystallinity and the loss of micropores volume. The Ni nanoclusters were uniformly confined in the mesopores of hierarchical HZSM-5 by the excessive impregnation method. The direct deoxygenation in N2 and hydrodeoxygenation in H2 of the methyl laurate were compared respectively over the Ni/HZSM-5 catalysts. In the N2 atmosphere, the deoxygenation rate of the methyl laurate on the Ni/HZSM-5 catalyst is relatively slow. In the presence of H2, the synergistic effect between the hydrogenation function of the metal and the acid function of the zeolite supports can make the deoxygenation level more obvious. The yield of hydrocarbon products gradually reached the maximum with the appropriate treatment concentration of 1M NaOH, which could be attributed to the improved mass transfer in the hierarchical HZSM-5 supports. Full article
(This article belongs to the Special Issue Zeolites and Catalysis)
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Open AccessArticle Catalytic Performance of Co3O4 on Different Activated Carbon Supports in the Benzyl Alcohol Oxidation
Catalysts 2017, 7(12), 384; doi:10.3390/catal7120384
Received: 22 September 2017 / Revised: 7 October 2017 / Accepted: 7 October 2017 / Published: 12 December 2017
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Abstract
Co3O4 particles were supported on a series of activated carbons (G60, CNR, RX3, and RB3). Incipient wetness method was used to prepare these catalysts. The effect of the structural and surface properties of the carbonaceous supports during oxidation of benzyl
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Co3O4 particles were supported on a series of activated carbons (G60, CNR, RX3, and RB3). Incipient wetness method was used to prepare these catalysts. The effect of the structural and surface properties of the carbonaceous supports during oxidation of benzyl alcohol was evaluated. The synthetized catalysts were characterized via IR, TEM, TGA/MS, XRD, TPR, AAS, XPS, and N2 adsorption/desorption isotherm techniques. Co3O4/G60 and Co3O4/RX3 catalysts have high activity and selectivity on the oxidation reaction reaching conversions above 90% after 6 h, without the presence of promoters. Catalytic performances show that differences in chemistry of support surface play an important role in activity and suggest that the presence of different ratios of species of cobalt and oxygenated groups on surface in Co3O4/G60 and Co3O4/RX3 catalysts, offered a larger effect synergic between both active phase and support increasing their catalytic activity when compared to the other tested catalysts. Full article
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Open AccessArticle Cu Nanoparticles/Fluorine-Doped Tin Oxide (FTO) Nanocomposites for Photocatalytic H2 Evolution under Visible Light Irradiation
Catalysts 2017, 7(12), 385; doi:10.3390/catal7120385
Received: 12 August 2017 / Revised: 29 September 2017 / Accepted: 29 September 2017 / Published: 12 December 2017
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Abstract
Copper nanoparticles/fluorine-doped tin oxide (FTO) nanocomposites were successfully prepared by a simple hydrothermal method. The synthesized nanocomposites were characterized by X-ray diffraction (XRD), UV-visible diffuse-reflectance spectrum (UV-VIS DRS), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Raman spectra, and X-ray photoelectron spectroscopy (XPS).
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Copper nanoparticles/fluorine-doped tin oxide (FTO) nanocomposites were successfully prepared by a simple hydrothermal method. The synthesized nanocomposites were characterized by X-ray diffraction (XRD), UV-visible diffuse-reflectance spectrum (UV-VIS DRS), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Raman spectra, and X-ray photoelectron spectroscopy (XPS). The obtained Cu/FTO nanocomposites exhibit high photocatalytic activity for H2 evolution under visible light (λ > 420 nm) irradiation. When the content of Cu is 19.2 wt % for FTO, the Cu/FTO photocatalyst shows the highest photocatalytic activity and the photocatalytic H2 evolution rate is up to 11.22 μmol·h−1. Meanwhile, the photocatalyst exhibits excellent stability and repeatability. It is revealed that the transfer efficiency of the photogenerated electrons is improved greatly because of the intense interaction between Cu NPs and FTO. Furthermore, a possible mechanism is proposed for enhanced photocatalytic H2 evolution of Cu/FTO photocatalysts under visible light irradiation. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessArticle Removal of NOX Using Hydrogen Peroxide Vapor over Fe/TiO2 Catalysts and an Absorption Technique
Catalysts 2017, 7(12), 386; doi:10.3390/catal7120386
Received: 17 October 2017 / Revised: 25 November 2017 / Accepted: 5 December 2017 / Published: 13 December 2017
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Abstract
In this study, we proposed an innovative oxidation–absorption method for low-temperature denitrification (160–240 °C), in which NO is initially catalytically oxidized by hydrogen peroxide (H2O2) vapor over titania-based catalysts, and the oxidation products are then absorbed by NaOH solution.
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In this study, we proposed an innovative oxidation–absorption method for low-temperature denitrification (160–240 °C), in which NO is initially catalytically oxidized by hydrogen peroxide (H2O2) vapor over titania-based catalysts, and the oxidation products are then absorbed by NaOH solution. The effects of flue gas temperature, molar H2O2/NO ratio, gas hourly space velocity (GHSV), and Fe substitution amounts of Fe/TiO2 catalysts on the denitrification efficiency were investigated by a well-designed experiment. The results indicated that the Fe/TiO2 catalyst exhibited a combination of remarkable activity and deep oxidation ability (NO converted into harmless NO3). In order to comprehend the functional mechanism of the Fe dopant’s local environment in TiO2 support, the promotional effect of the calcination temperature of Fe/TiO2 on the denitration performance was also studied. A tentative synergetic mechanism could be interpreted from two aspects: (1) Fe3+ as a substitute of Ti4+, leading to the formation of enriched oxygen vacancies at the surface, could significantly improve the adsorption efficiency of •OH; (2) the isolated surface Fe ion holds a strong adsorption affinity for NO, such that the adsorbed NO could be easily oxidized by the pre-formed •OH. This process offers a promising alternative for current denitrification technology. Full article
(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)
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Open AccessCommunication Catalytic Enantioselective Addition of Me2Zn to Isatins
Catalysts 2017, 7(12), 387; doi:10.3390/catal7120387
Received: 15 November 2017 / Revised: 7 December 2017 / Accepted: 8 December 2017 / Published: 13 December 2017
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Abstract
Chiral α-hydroxyamide L5 derived from (S)-(+)-mandelic acid catalyzes the enantioselective addition of dimethylzinc to isatins affording the corresponding chiral 3-hydroxy-3-methyl-2-oxindoles with good yields and er up to 90:10. Furthermore, several chemical transformations were performed with the 3-hydroxy-2-oxindoles obtained. Full article
(This article belongs to the Special Issue Catalyzed Synthesis of Natural Products)
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Open AccessFeature PaperArticle Understanding the Heteroatom Effect on the Ullmann Copper-Catalyzed Cross-Coupling of X-Arylation (X = NH, O, S) Mechanism
Catalysts 2017, 7(12), 388; doi:10.3390/catal7120388
Received: 14 November 2017 / Revised: 7 December 2017 / Accepted: 11 December 2017 / Published: 13 December 2017
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Abstract
Density Functional Theory (DFT) calculations have been carried out in order to unravel the governing reaction mechanism in copper-catalyzed cross-coupling Ullmann type reactions between iodobenzene (1, PhI) and aniline (2-NH, PhNH2), phenol (2-O, PhOH) and
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Density Functional Theory (DFT) calculations have been carried out in order to unravel the governing reaction mechanism in copper-catalyzed cross-coupling Ullmann type reactions between iodobenzene (1, PhI) and aniline (2-NH, PhNH2), phenol (2-O, PhOH) and thiophenol (2-S, PhSH) with phenanthroline (phen) as the ancillary ligand. Four different pathways for the mechanism were considered namely Oxidative Addition–Reductive Elimination (OA-RE), σ-bond Metathesis (MET), Single Electron Transfer (SET), and Halogen Atom Transfer (HAT). Our results suggest that the OA-RE route, involving CuIII intermediates, is the energetically most favorable pathway for all the systems considered. Interestingly, the rate-determining step is the oxidative addition of the phenyl iodide to the metal center regardless of the nature of the heteroatom. The computed energy barriers in OA increase in the order O < S < NH. Using the Activation Strain Model (ASM) of chemical reactivity, it was found that the strain energy associated with the bending of the copper(I) complex controls the observed reactivity. Full article
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Open AccessFeature PaperArticle In Silico Switch from Second- to First-Row Transition Metals in Olefin Metathesis: From Ru to Fe and from Rh to Co
Catalysts 2017, 7(12), 389; doi:10.3390/catal7120389
Received: 20 November 2017 / Revised: 9 December 2017 / Accepted: 11 December 2017 / Published: 14 December 2017
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Abstract
Density functional theory (DFT) calculations have been used to investigate the behavior of different transition metals from Groups 8 (Fe and Ru) and 9 (Co and Rh) in an already well-known catalytic mechanism, which is based on an Ru(SIMes)(PPh3)Cl2=CH(Ph)
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Density functional theory (DFT) calculations have been used to investigate the behavior of different transition metals from Groups 8 (Fe and Ru) and 9 (Co and Rh) in an already well-known catalytic mechanism, which is based on an Ru(SIMes)(PPh3)Cl2=CH(Ph) complex. As expected, Ru has proven to perform better than their Fe, Co, and Rh counterparts. Even though the topographic steric maps analysis shows no difference in sterical hindrance for any of the metal centers, geometrically, the Fe-based species show a high rigidity with shorter and stronger bonds confirmed by Mayer Bond Orders. The systems bearing Co as a metallic center might present a reactivity that is, surprisingly, too high according to conceptual DFT, which would consequently be a drawback for the formation of the fundamental species of the reaction pathway: the metallacycle intermediate. Full article
(This article belongs to the Special Issue Catalysis of Olefin Metathesis)
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Open AccessArticle A Green Route to Copper Loaded Silica Nanoparticles Using Hyperbranched Poly(Ethylene Imine) as a Biomimetic Template: Application in Heterogeneous Catalysis
Catalysts 2017, 7(12), 390; doi:10.3390/catal7120390
Received: 24 November 2017 / Revised: 8 December 2017 / Accepted: 11 December 2017 / Published: 14 December 2017
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Abstract
Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and
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Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and neutral pH, through a biomimetic silicification process. Furthermore, the derived hybrid organic/inorganic materials dispersed in water can be easily loaded with various copper amounts, due to the presence of PEI, which, despite having been integrated in the silica network, retains its strong copper chelating ability. Following calcination, the obtained copper loaded nanopowders are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), N2 adsorption, Temperature programmed reduction (TPR) and UV-Vis diffuse reflectance (UV-Vis-DR) techniques and evaluated for automotive exhaust purification under simulated conditions at the stoichiometric point. Effective control over final materials’ pore structural and morphological characteristics is provided by employing different buffer solutions, i.e., tris(hydroxymethyl)aminomethane (Tris) or phosphate buffer. It was found that the enhancement of the nanopowders textural features, obtained in the presence of Tris buffer, had a great impact on the material’s catalytic behavior, improving significantly its activity towards pollutants oxidation. Full article
(This article belongs to the Special Issue Nanostructured Materials for Applications in Heterogeneous Catalysis)
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Open AccessArticle Mixed Zinc/Manganese on Highly Reduced Graphene Oxide: A Highly Active Nanocomposite Catalyst for Aerial Oxidation of Benzylic Alcohols
Catalysts 2017, 7(12), 391; doi:10.3390/catal7120391 (registering DOI)
Received: 29 November 2017 / Revised: 11 December 2017 / Accepted: 12 December 2017 / Published: 15 December 2017
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Abstract
Nanocomposites of highly reduced graphene oxide (HRG) and ZnOx nanoparticles doped manganese carbonate containing different percentages of HRG were prepared via a facile co-precipitation method. The prepared sample calcined at 300 °C yielded i.e., ZnOx(1%)–MnCO3/)X%(HRG (where X =
[...] Read more.
Nanocomposites of highly reduced graphene oxide (HRG) and ZnOx nanoparticles doped manganese carbonate containing different percentages of HRG were prepared via a facile co-precipitation method. The prepared sample calcined at 300 °C yielded i.e., ZnOx(1%)–MnCO3/)X%(HRG (where X = 0–7), calcination at 400 °C and 500 °C, yielded different manganese oxides i.e., ZnOx(1%)–MnO2/)X%(HRG and ZnOx(1%)–Mn2O3/)X%(HRG respectively. The prepared catalyst were subjected to catalytic evaluation and a comparative catalytic study between carbonates and oxides for the liquid-phase aerobic oxidation of benzylic alcohols to corresponding aldehydes using molecular oxygen as an eco-friendly oxidant without adding additives or bases. The influence of various parameters such as percentage of HRG, reaction time, catalyst amount, calcination and reaction temperature was systematically examined to optimize reaction conditions using oxidation of benzyl alcohol as a substrate model. It was found that the catalytic performance is remarkably enhanced after using HRG as catalyst co-dopant for the aerobic oxidation of alcohols, possibly owing to the presence of carbon defects and oxygenated functional groups on HRG surface. The as-synthesized catalysts were characterized by SEM, EDX, XRD, Raman, TGA, BET, and FT-IR. Under optimal conditions, the catalyst with composition ZnOx(1%)–MnCO3/)1%(HRG calcined at 300 °C exhibited remarkable specific activity (57.1 mmol·g−1·h−1) with 100% conversion of benzyl alcohol and more than 99% product selectivity within extremely short time (7 min). The as-prepared catalyst was re-used up to five consecutive times without significant decrease in its activity and selectivity. To the best of our knowledge, the achieved specific activity is the highest so far compared to the earlier reported catalysts used for the benzyl alcohol oxidation. A wide range of substituted benzylic and aliphatic alcohols were selectively oxidized into their corresponding aldehydes with complete convertibility and selectivity in short reaction times without over-oxidation to the acids. Due to their significant low cost, superior reproducibility, excellent catalytic efficiency, the ZnOx(1%)–MnCO3/)X%(HRG nanocomposites possess several application prospect in other organic chemistry reactions. Full article
(This article belongs to the Special Issue Nanostructured Materials for Applications in Heterogeneous Catalysis)
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Open AccessArticle Preparation of Manganese Lignosulfonate and Its Application as the Precursor of Nanostructured MnOx for Oxidative Electrocatalysis
Catalysts 2017, 7(12), 392; doi:10.3390/catal7120392 (registering DOI)
Received: 6 November 2017 / Revised: 11 December 2017 / Accepted: 13 December 2017 / Published: 15 December 2017
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Abstract
The synthesis of manganese lignosulfonates by a two-step method has been reported. It was based on the conversion of technical sodium derivative of lignosulfonate to its hydrogen form i.e., lignosulfonic acid and its further reaction with manganese hydroxide. The obtained product was electroactive,
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The synthesis of manganese lignosulfonates by a two-step method has been reported. It was based on the conversion of technical sodium derivative of lignosulfonate to its hydrogen form i.e., lignosulfonic acid and its further reaction with manganese hydroxide. The obtained product was electroactive, and could be applied as the precursor of electroactive manganese oxide. The product showed a reversible redox activity in the potential range of 0 to 1 V vs. an Ag/AgCl reference electrode. The electroactivity of the obtained product can be tentatively assigned to the redox activity of both the electrodeposited MnOx and the presence of lignosulfonate-derived quinones since the energy dispersive spectroscopy (EDS) confirmed the presence of organic matter in the deposit. It also showed substantial electrocatalytic activity towards the anodic oxidation of hydrogen peroxide. This suggests that manganese lignosulfonates could be a valuable compound for the electrochemical preparation of electroactive layers that are suitable in the development of electrochemical sensors. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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Open AccessReview Strategies to Enhance the Catalytic Performance of ZSM-5 Zeolite in Hydrocarbon Cracking: A Review
Catalysts 2017, 7(12), 367; doi:10.3390/catal7120367
Received: 30 October 2017 / Revised: 20 November 2017 / Accepted: 21 November 2017 / Published: 29 November 2017
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Abstract
ZSM-5 zeolite is widely used in catalytic cracking of hydrocarbon, but the conventional ZSM-5 zeolite deactivates quickly due to its simple microporous and long diffusion pathway. Many studies have been done to overcome these disadvantages recently. In this review, four main approaches for
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ZSM-5 zeolite is widely used in catalytic cracking of hydrocarbon, but the conventional ZSM-5 zeolite deactivates quickly due to its simple microporous and long diffusion pathway. Many studies have been done to overcome these disadvantages recently. In this review, four main approaches for enhancing the catalytic performance, namely synthesis of ZSM-5 zeolite with special morphology, hierarchical ZSM-5 zeolite, nano-sized ZSM-5 zeolite and optimization of acid properties, are discussed. ZSM-5 with special morphology such as hollow, composite and nanosheet structure can effectively increase the diffusion efficiency and accessibility of acid sites, giving high catalytic activity. The accessibility of acid sites and diffusion efficiency can also be enhanced by introducing additional mesopores or macropores. By decreasing the crystal size to nanoscale, the diffusion length can be shortened. The catalytic activity increases and the amount of carbon deposition decreases with the decrease of crystal size. By regulating the acid properties of ZSM-5 with element or compound modification, the overreaction of reactants and formation of carbon deposition could be suppressed, thus enhancing the catalytic activity and light alkene selectivity. Besides, some future needs and perspectives of ZSM-5 with excellent cracking activity are addressed for researchers’ consideration. Full article
(This article belongs to the Special Issue Zeolites and Catalysis)
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Open AccessReview Recent Advances in Transition-Metal-Mediated Electrocatalytic CO2 Reduction: From Homogeneous to Heterogeneous Systems
Catalysts 2017, 7(12), 373; doi:10.3390/catal7120373
Received: 10 October 2017 / Revised: 13 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
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Abstract
Global climate change and increasing demands for clean energy have brought intensive interest in the search for proper electrocatalysts in order to reduce carbon dioxide (CO2) to higher value carbon products such as hydrocarbons. Recently, transition-metal-centered molecules or organic frameworks have
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Global climate change and increasing demands for clean energy have brought intensive interest in the search for proper electrocatalysts in order to reduce carbon dioxide (CO2) to higher value carbon products such as hydrocarbons. Recently, transition-metal-centered molecules or organic frameworks have been reported to show outstanding electrocatalytic activity in the liquid phase. Their d-orbital electrons are believed to be one of the key factors to capture and convert CO2 molecules to value-added low-carbon fuels. In this review, recent advances in electrocatalytic CO2 reduction have been summarized based on the targeted products, ranging from homogeneous reactions to heterogeneous ones. Their advantages and fallbacks have been pointed out and the existing challenges, especially with respect to the practical and industrial application are addressed. Full article
(This article belongs to the Special Issue Nanostructured Materials for Applications in Heterogeneous Catalysis)
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Open AccessFeature PaperReview Recent Advances in Rare Earth Complexes Bearing Allyl Ligands and Their Reactivity towards Conjugated Dienes and Styrene Polymerization
Catalysts 2017, 7(12), 378; doi:10.3390/catal7120378
Received: 15 November 2017 / Revised: 29 November 2017 / Accepted: 30 November 2017 / Published: 5 December 2017
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Abstract
This mini-review focuses on recent advances on the synthesis, structure, and characterization of allyl-based rare earth organometallic complexes, with emphasis on their ability to catalyze the polymerization of non-polar monomers such as conjugated dienes, styrene, and their related copolymerization. Full article
(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)
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Open AccessReview Direct Carboxylation of C(sp3)-H and C(sp2)-H Bonds with CO2 by Transition-Metal-Catalyzed and Base-Mediated Reactions
Catalysts 2017, 7(12), 380; doi:10.3390/catal7120380
Received: 20 October 2017 / Revised: 21 November 2017 / Accepted: 24 November 2017 / Published: 7 December 2017
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Abstract
This review focuses on recent advances in the field of direct carboxylation reactions of C(sp3)-H and C(sp2)-H bonds using CO2 encompassing both transition-metal-catalysis and base-mediated approach. The review is not intended to be comprehensive, but aims to analyze
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This review focuses on recent advances in the field of direct carboxylation reactions of C(sp3)-H and C(sp2)-H bonds using CO2 encompassing both transition-metal-catalysis and base-mediated approach. The review is not intended to be comprehensive, but aims to analyze representative examples from the literature, including transition-metal catalyzed carboxylation of benzylic and allylic C(sp3)-H functionalities using CO2 which is at a “nascent stage”. Examples of light-driven carboxylation reactions of unactivated C(sp3)-H bonds are also considered. Concerning C(sp3)-H and C(sp2)-H deprotonation reactions mediated by bases with subsequent carboxylation of the carbon nucleophile, few examples of catalytic processes are reported in the literature. In spite of this, several examples of base-promoted reactions integrating “base recycling” or “base regeneration (through electrosynthesis)” steps have been reported. Representative examples of synthetically efficient, base-promoted processes are included in the review. Full article
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