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Catalysts, Volume 7, Issue 8 (August 2017)

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Cover Story Lipase-catalyzed esterification reactions between short chain fatty acids and alcohols are widely [...] Read more.
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Editorial

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Open AccessEditorial Heterogeneous Catalysis for Environmental Remediation
Catalysts 2017, 7(8), 236; doi:10.3390/catal7080236
Received: 11 August 2017 / Revised: 11 August 2017 / Accepted: 15 August 2017 / Published: 16 August 2017
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Abstract
The intensive human activities in chemical industry and environmental purification urge the development of advanced protocols for green production and waste management. [...]
Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)

Research

Jump to: Editorial, Review

Open AccessFeature PaperArticle Mesoporous ZSM-5 Zeolites in Acid Catalysis: Top-Down vs. Bottom-Up Approach
Catalysts 2017, 7(8), 225; doi:10.3390/catal7080225
Received: 26 May 2017 / Revised: 14 July 2017 / Accepted: 19 July 2017 / Published: 26 July 2017
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Abstract
A top-down desilication of Al-rich ZSM-5 zeolites and a bottom-up mesopores creating method were evaluated in this study. Three liquid–solid and one gas–solid heterogeneously-catalysed reactions were chosen to establish relationships between zeolites textural properties and their catalytic behavior in acid-catalysed model reactions that
[...] Read more.
A top-down desilication of Al-rich ZSM-5 zeolites and a bottom-up mesopores creating method were evaluated in this study. Three liquid–solid and one gas–solid heterogeneously-catalysed reactions were chosen to establish relationships between zeolites textural properties and their catalytic behavior in acid-catalysed model reactions that are influenced by shape selectivity: Diels-Alder cyclization between isoprene and methylacrylate, Methanol-to-Olefins (MTO) reaction, chlorination of iodobenzene with trichloroisocyanuric acid (TCCA), and Friedel-Crafts acylation of anisole by carboxylic acids with differing sizes. It is found amongst others that no optimal mesoporosity for all the different reactions can be easily obtained, but depending on the chosen application, a specific treatment has to be set to achieve high activity/selectivity and stability. Full article
(This article belongs to the Special Issue Zeolites and Catalysis)
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Open AccessArticle Renewable Hydrogen from Ethanol Reforming over CeO2-SiO2 Based Catalysts
Catalysts 2017, 7(8), 226; doi:10.3390/catal7080226
Received: 14 June 2017 / Revised: 19 July 2017 / Accepted: 26 July 2017 / Published: 27 July 2017
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Abstract
In this research, a bimetallic Pt-Ni/CeO2-SiO2 catalyst, synthetized via wet impregnation, was successfully employed for the oxidative steam reforming of ethanol between 300 and 600 °C. The reaction performance of the Pt-Ni catalyst was investigated and compared with the Ni/CeO
[...] Read more.
In this research, a bimetallic Pt-Ni/CeO2-SiO2 catalyst, synthetized via wet impregnation, was successfully employed for the oxidative steam reforming of ethanol between 300 and 600 °C. The reaction performance of the Pt-Ni catalyst was investigated and compared with the Ni/CeO2-SiO2, Pt/CeO2-SiO2 as well as CeO2-SiO2 sample. The bimetallic catalyst displayed the best results in terms of hydrogen yield and by-products selectivity, thus highlighting the crucial role of active species (Pt and Ni) in promoting ethanol conversion and reaching the products distribution predicted by thermodynamics. The most promising sample, tested at 500 °C for more than 120 h, assured total conversion and no apparent deactivation, demonstrating the stability of the selected formulation. By changing contact time, the dependence of carbon formation rate on space velocity was also investigated. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors)
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Open AccessArticle Effect of Water Clustering on the Activity of Candida antarctica Lipase B in Organic Medium
Catalysts 2017, 7(8), 227; doi:10.3390/catal7080227
Received: 10 July 2017 / Revised: 21 July 2017 / Accepted: 25 July 2017 / Published: 29 July 2017
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Abstract
The effect of initial water activity of MTBE (methyl tert-butyl ether) medium on CALB (Candida antarctica lipase B) catalyzed esterification reaction is investigated using experimental methods and classical molecular dynamics (MD) simulations. The experimental kinetic studies show that the initial reaction
[...] Read more.
The effect of initial water activity of MTBE (methyl tert-butyl ether) medium on CALB (Candida antarctica lipase B) catalyzed esterification reaction is investigated using experimental methods and classical molecular dynamics (MD) simulations. The experimental kinetic studies show that the initial reaction rate of CALB-catalyzed esterification reaction between butyric acid and ethanol decreases with increasing initial water activity of the medium. The highest rate of esterification is observed at the lowest water activity studied. MD simulations were performed to gain a molecular insight on the effect of initial water activity on the rate of CALB-catalyzed reaction. Our results show that hydration has an insignificant effect on the structure and flexibility of CALB. Rather, it appears that water molecules bind to certain regions (“hot spots”) on the CALB surface and form clusters. The size of the water clusters at these hot spot regions gradually increase and expand with increasing water activity. Consequently, the surface area of CALB covered by the water molecules also increases. Specifically, our results indicate that a particular water cluster located close to the active site partially cover the binding pocket of substrate at high water activity. As a consequence, the effective concentration of substrate at the catalytic site decreases. Therefore, the reaction rate slows down with increasing water activity, which correlates well with the observed decrease in the experimentally determined initial reaction rate. Full article
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Open AccessCommunication Direct Conversion of Propylene Oxide to 3-Hydroxy Butyric Acid Using a Cobalt Carbonyl Ionic Liquid Catalyst
Catalysts 2017, 7(8), 228; doi:10.3390/catal7080228
Received: 15 June 2017 / Revised: 22 July 2017 / Accepted: 27 July 2017 / Published: 30 July 2017
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Abstract
The reported catalytic system demonstrates the possibility of efficient mass production of 3-hydroxybutyric acid (3-HBA) from inexpensive raw materials. The direct coupling of propylene oxide, water, and CO was catalyzed by 1-butyl-3-methylimidazolium cobalt tetracarbonyl ([Bmim][Co(CO)4]) ionic liquid to form 3-HBA with
[...] Read more.
The reported catalytic system demonstrates the possibility of efficient mass production of 3-hydroxybutyric acid (3-HBA) from inexpensive raw materials. The direct coupling of propylene oxide, water, and CO was catalyzed by 1-butyl-3-methylimidazolium cobalt tetracarbonyl ([Bmim][Co(CO)4]) ionic liquid to form 3-HBA with >99% conversion (49% selectivity) under mild conditions. Full article
(This article belongs to the Special Issue Organocatalysis in Ionic Liquids)
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Open AccessFeature PaperArticle Fast and Large-Scale Anodizing Synthesis of Pine-Cone TiO2 for Solar-Driven Photocatalysis
Catalysts 2017, 7(8), 229; doi:10.3390/catal7080229
Received: 6 July 2017 / Revised: 24 July 2017 / Accepted: 27 July 2017 / Published: 1 August 2017
Cited by 1 | PDF Full-text (5355 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Anodization has been widely used to synthesize nanostructured TiO2 films with promising photocatalytic performance for solar hydrogen production and pollution removal. However, it usually takes a few hours to obtain the right nanostructures even on a small scale (e.g., 10 mm ×
[...] Read more.
Anodization has been widely used to synthesize nanostructured TiO2 films with promising photocatalytic performance for solar hydrogen production and pollution removal. However, it usually takes a few hours to obtain the right nanostructures even on a small scale (e.g., 10 mm × 20 mm). In order to attract interest for industrial applications, fast and large-scale fabrication is highly desirable. Herein, we demonstrate a fast and large-scale (e.g., 300 mm × 360 mm) synthesis of pine-cone TiO2 nanostructures within two min. The formation mechanism of pine-cone TiO2 is proposed. The pine-cone TiO2 possesses a strong solar absorption, and exhibits high photocatalytic activities in photo-oxidizing organic pollutants in wastewater and producing hydrogen from water under natural sunlight. Thus, this study demonstrates a promising method for fabricating TiO2 films towards practical photocatalytic applications. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessFeature PaperArticle Catalytic Performance of Fe(II)-Scorpionate Complexes towards Cyclohexane Oxidation in Organic, Ionic Liquid and/or Supercritical CO2 Media: A Comparative Study
Catalysts 2017, 7(8), 230; doi:10.3390/catal7080230
Received: 27 June 2017 / Revised: 23 July 2017 / Accepted: 26 July 2017 / Published: 2 August 2017
Cited by 1 | PDF Full-text (1135 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The catalytic activity of the iron(II) C-scorpionate complexes [FeCl2{HC(pz)3}] 1 (pz = pyrazol-1-yl) and [FeCl2{HOCH2C(pz)3}] 2, and of their precursor FeCl2·2H2O 3, towards cyclohexane oxidation with tert
[...] Read more.
The catalytic activity of the iron(II) C-scorpionate complexes [FeCl2{HC(pz)3}] 1 (pz = pyrazol-1-yl) and [FeCl2{HOCH2C(pz)3}] 2, and of their precursor FeCl2·2H2O 3, towards cyclohexane oxidation with tert-butyl hydroperoxide was evaluated and compared in different media: acetonitrile, ionic liquids (1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], and 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, [bmim][FAP]), supercritical carbon dioxide (scCO2), and scCO2/[bmim][X] (X = PF6 or FAP) mixtures. The use of such alternative solvents led to efficient and selective protocols for the oxidation of cyclohexane. Moreover, tuning the alcohol/ketone selectivity was possible by choosing the suitable solvent. Full article
(This article belongs to the Special Issue Catalysis in Innovative Solvents)
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Open AccessFeature PaperArticle Is Selective Heating of the Sulfonic Acid Catalyst AC-SO3H by Microwave Radiation Crucial in the Acid Hydrolysis of Cellulose to Glucose in Aqueous Media?
Catalysts 2017, 7(8), 231; doi:10.3390/catal7080231
Received: 1 July 2017 / Revised: 23 July 2017 / Accepted: 1 August 2017 / Published: 8 August 2017
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Abstract
Selective heating of microwave-absorbing solid catalysts in a heterogeneous medium may affect a chemical reaction; such selectivity cannot be achieved by conventional oil-bath or steam heating methods. Moreover, microwave methods are often misunderstood with respect to equipment and temperature measurements, so that additional
[...] Read more.
Selective heating of microwave-absorbing solid catalysts in a heterogeneous medium may affect a chemical reaction; such selectivity cannot be achieved by conventional oil-bath or steam heating methods. Moreover, microwave methods are often misunderstood with respect to equipment and temperature measurements, so that additional experimentation is necessary. In this regard, the present study intended to clarify the effect of microwave selective heating on acid hydrolytic processes using a sulfonated activated carbon catalyst (AC-SO3H). The model reaction chosen was the acid hydrolysis of cellulose carried out in a Pyrex glass microwave reactor, with the process being monitored by examining the quantity of total sugar, reducing sugar, and glucose produced. Heat transfer from the catalyst to the aqueous solution through absorption of microwaves by the catalyst occurred as predicted from a simulation of heat transfer processes. The resulting experimental consequences are compared with those from the more uniform microwave conduction heating method by also performing the reaction in a SiC microwave reactor wherein microwaves are absorbed by SiC. Some inferences of the influence of microwave selective heating of carbon-based catalyst particles are reported. Under selective heating conditions (Pyrex glass reactor), the yield of glucose from the acid hydrolysis of cellulose was 56% upon microwave heating at 200 °C, nearly identical with the yield (55%) when the hydrolytic process was performed under mainly conventional heating conditions in the SiC reactor. Although the beneficial effect of catalyst selective heating was not reflected in the reaction efficiency, there were substantial changes in the state of adsorption of cellulose on the catalyst surface. Full article
(This article belongs to the Special Issue Enabling Technologies toward Green Catalysis)
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Open AccessArticle Functionalization of SSZ-13 and Fe-Beta with Copper by NH3 and NO Facilitated Solid-State Ion-Exchange
Catalysts 2017, 7(8), 232; doi:10.3390/catal7080232
Received: 7 July 2017 / Revised: 24 July 2017 / Accepted: 4 August 2017 / Published: 8 August 2017
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Abstract
We show that functionalization of SSZ-13 (CHA) and Fe-beta (*BEA) with copper using a recently reported solid-state ion-exchange method, facilitated by NH3 and nitrogen oxides (NO), is a viable route to prepare Cu-SSZ-13 and (Cu + Fe)-beta catalysts, starting from H-SSZ-13 and
[...] Read more.
We show that functionalization of SSZ-13 (CHA) and Fe-beta (*BEA) with copper using a recently reported solid-state ion-exchange method, facilitated by NH 3 and nitrogen oxides (NO), is a viable route to prepare Cu-SSZ-13 and (Cu + Fe)-beta catalysts, starting from H-SSZ-13 and Fe-beta, respectively. The physicochemical properties of the prepared catalysts are characterized by XRD, UV-Vis-spectroscopy and STEM-EDS, confirming that copper originally present in the physical mixture of CuO and H-SSZ-13, and CuO and Fe-beta, is inserted into the micropores of SSZ-13 and Fe-beta, respectively. Activity measurements in gas-flow reactor show that the samples are active for NO reduction by NH 3 -SCR over a broad temperature range, i.e., 150–500 C. For the Cu-SSZ-13 catalysts, which have a copper loading range of 0.5–4 wt. %, the sample prepared from the physical mixture with a CuO/SSZ-13 ratio corresponding to 2 wt. % Cu is the most active catalyst for NH 3 -SCR under the present reaction conditions. Furthermore, the (Cu + Fe)-beta catalyst shows higher NH 3 -SCR activity over a broader temperature range and especially at low temperature as compared to the Fe-beta and Cu-beta counterparts. The results encourage further elaboration on sequential ion-exchange procedures for bimetallic functionalization of zeolites. Full article
(This article belongs to the Special Issue Zeolites and Catalysis)
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Open AccessFeature PaperArticle Selective Alkylation of Benzene by Propane over Bifunctional Pd-Acid Catalysts
Catalysts 2017, 7(8), 233; doi:10.3390/catal7080233
Received: 12 July 2017 / Revised: 4 August 2017 / Accepted: 8 August 2017 / Published: 11 August 2017
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Abstract
The alkylation of benzene by propane to yield isopropylbenzene (iPrPh) was studied using bifunctional Pd-acid catalysts, such as Pd-heteropoly acid and Pd-zeolite, in a fixed bed reactor at 300 °C and 1 bar pressure. Keggin-type tungstosilicic acid H4SiW12O40
[...] Read more.
The alkylation of benzene by propane to yield isopropylbenzene (iPrPh) was studied using bifunctional Pd-acid catalysts, such as Pd-heteropoly acid and Pd-zeolite, in a fixed bed reactor at 300 °C and 1 bar pressure. Keggin-type tungstosilicic acid H4SiW12O40 (HSiW) and zeolite HZSM-5 were used as the acid components in these catalysts. The reaction occurred most efficiently over 2%Pd/25%HSiW/SiO2, giving iPrPh with up to 88% selectivity. The Pd-HSiW catalyst was more selective than the Pd-HZSM-5; the latter gave only 11–18% iPrPh selectivity. The reaction proceeded via a bifunctional mechanism including the dehydrogenation of propane to form propene on Pd sites, followed by the alkylation of benzene with the propene on acid sites. The effect of Pd loading in Pd-HSiW and Pd-HZSM-5 catalysts indicated that the first step reached quasi-equilibrium at 1.5–2% Pd loading and the second step became rate limiting. The addition of gold to Pd-HSiW enhanced the activity of this catalyst, although the Au-HSiW without Pd was inert. Full article
(This article belongs to the Special Issue Recent Advances in Polyoxometalate-Catalyzed Reactions)
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Open AccessArticle Efficient Catalytic Upgrading of Levulinic Acid into Alkyl Levulinates by Resin-Supported Acids and Flow Reactors
Catalysts 2017, 7(8), 235; doi:10.3390/catal7080235
Received: 24 July 2017 / Revised: 7 August 2017 / Accepted: 9 August 2017 / Published: 15 August 2017
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Abstract
Biomass-derived levulinic acid (LA) is an excellent substrate to obtain high-value esters that can be used as second-generation biofuels and biofuel additives. The present study focuses on the identification and definition of the key parameters crucial for the development of chemically and environmentally
[...] Read more.
Biomass-derived levulinic acid (LA) is an excellent substrate to obtain high-value esters that can be used as second-generation biofuels and biofuel additives. The present study focuses on the identification and definition of the key parameters crucial for the development of chemically and environmentally efficient protocols operating in continuous-flow for the preparation of structurally diverse alkyl levulinates via the esterification of LA. We have focused on the use of solid acid catalysts consisting of sulfonated cation exchange resins and considered different aliphatic alcohols to prepare levulinates 3 and 11–17 regioselectively, and in good to high yields (50–92%). Direct correlations between several reaction parameters and catalyst activity have been investigated and discussed to set proper flow reactors that allow minimal waste production during the workup procedure, enabling Environmental factor (E-factor) values as low as ca. 0.3, full recoverability and reusability of the catalysts, and the production of levulinates up to ca. 5 gxh−1 scale. Full article
(This article belongs to the Special Issue Enabling Technologies toward Green Catalysis)
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Open AccessArticle Facile, One-Pot, Two-Step, Strategy for the Production of Potential Bio-Diesel Candidates from Fructose
Catalysts 2017, 7(8), 237; doi:10.3390/catal7080237
Received: 23 June 2017 / Revised: 28 July 2017 / Accepted: 12 August 2017 / Published: 17 August 2017
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Abstract
The production of bio-diesel fuels from carbohydrates is a promising alternative to fossil fuels with regard to the growing severity of the environmental problem and energy crisis. Potential bio-diesel candidates or additives, such as 5-(hydroxymethyl)-2-(dimethoxymethyl) furan (HDMF), 2-(dimethoxymethyl)-5-(methoxymethyl) furan (DMMF), and 5-(methoxymethyl)-2-furaldehyde (MMF)
[...] Read more.
The production of bio-diesel fuels from carbohydrates is a promising alternative to fossil fuels with regard to the growing severity of the environmental problem and energy crisis. Potential bio-diesel candidates or additives, such as 5-(hydroxymethyl)-2-(dimethoxymethyl) furan (HDMF), 2-(dimethoxymethyl)-5-(methoxymethyl) furan (DMMF), and 5-(methoxymethyl)-2-furaldehyde (MMF) could be produced from the alcoholic solutions of both 5-HMF and fructose in the presence of solid acid catalysts. In the present study, a readily prepared, silica, gel-supported nitric acid (SiO2-HNO3) catalyst was found to be exceptionally reactive for the production of HDMF from fructose. A DMSO-methanol biphasic solvent system was developed and HDMF, DMMF, and MMF were observed at 150 °C, with maximum yields of 34%, 34%, and 25%, respectively. Meanwhile, a maximum HDMF yield of 77% was obtained from 5-HMF in methanol. Moreover, a sequential, one-pot, two-step dehydration/acetalization process, involving the dehydration of fructose to 5-HMF in dimethylsulfoxide (DMSO) at 150 °C, and followed by adding a certain amount of methanol to react with the formed 5-HMF to HDMF at 100 °C, was developed to promote the yield of HDMF. The optimum yield of HDMF reached 70% with the complete conversion of fructose. The reaction mechanisms of dehydration and acetalization have been proposed for the conversion of 5-HMF to HDMF. The two-step design allows for facile catalyst recycling while supplying as a promising method for the production of biodiesel from complex carbohydrates. Full article
(This article belongs to the Special Issue Catalysis of Biomass-Derived Molecules)
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Open AccessArticle Enzymatic Synthesis of S-Adenosylmethionine Using Immobilized Methionine Adenosyltransferase Variants on the 50-mM Scale
Catalysts 2017, 7(8), 238; doi:10.3390/catal7080238
Received: 17 July 2017 / Revised: 13 August 2017 / Accepted: 14 August 2017 / Published: 17 August 2017
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Abstract
S-adenosylmethionine (SAM), an important metabolite in all living organisms, has been widely used to treat various diseases. To develop a simple and efficient method to produce SAM, an engineered variant of the methionine adenosyltransferase (MAT) from Escherichia coli was investigated for its
[...] Read more.
S-adenosylmethionine (SAM), an important metabolite in all living organisms, has been widely used to treat various diseases. To develop a simple and efficient method to produce SAM, an engineered variant of the methionine adenosyltransferase (MAT) from Escherichia coli was investigated for its potential use in the enzymatic synthesis of SAM due to its significantly decreased product inhibition. The recombinant I303V MAT variant was successfully produced at a high level (~800 mg/L) with approximately four-fold higher specific activity than the wild-type MAT. The recombinant I303V MAT was covalently immobilized onto the amino resin and epoxy resin in order to obtain a robust biocatalyst to be used in industrial bioreactors. The immobilized preparation using amino resin exhibited the highest activity coupling yield (~84%), compared with approximately 3% for epoxy resin. The immobilized enzyme was more stable than the soluble enzyme under the reactive conditions, with a half-life of 229.5 h at 37 °C. The KmATP value (0.18 mM) of the immobilized enzyme was ca. two-fold lower than that of the soluble enzyme. Furthermore, the immobilized enzyme showed high operational stability during 10 consecutive 8 h batches, with the substrate adenosine triphosphate (ATP) conversion rate above 95% on the 50-mM scale. Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
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Open AccessArticle The Differentiating Polarization Curve Technique for the Tafel Parameter Estimation
Catalysts 2017, 7(8), 239; doi:10.3390/catal7080239
Received: 21 July 2017 / Revised: 11 August 2017 / Accepted: 14 August 2017 / Published: 17 August 2017
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Abstract
An experimentally obtained polarization curve for the hydrogen evolution reaction on silver in a 0.5 mol dm−3 solution was investigated using an electrochemical curve technique named the differential polarization method (DPM). The exchange current density estimated by the Tafel extrapolation method (TEM)
[...] Read more.
An experimentally obtained polarization curve for the hydrogen evolution reaction on silver in a 0.5 mol dm−3 solution was investigated using an electrochemical curve technique named the differential polarization method (DPM). The exchange current density estimated by the Tafel extrapolation method (TEM) and the DPM were compared and assessed from points of simple and more accurate handling. It is shown that the DPM has two advantages: (1) proper reading of the Tafel slope region and (2) elimination of the undesirable physical factors such as oxide film and solution resistance. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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Open AccessCommunication Enzymatic Oxyfunctionalization Driven by Photosynthetic Water-Splitting in the Cyanobacterium Synechocystis sp. PCC 6803
Catalysts 2017, 7(8), 240; doi:10.3390/catal7080240
Received: 8 July 2017 / Revised: 10 August 2017 / Accepted: 10 August 2017 / Published: 17 August 2017
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Abstract
Photosynthetic water-splitting is a powerful force to drive selective redox reactions. The need of highly expensive redox partners such as NADPH and their regeneration is one of the main bottlenecks for the application of biocatalysis at an industrial scale. Recently, the possibility of
[...] Read more.
Photosynthetic water-splitting is a powerful force to drive selective redox reactions. The need of highly expensive redox partners such as NADPH and their regeneration is one of the main bottlenecks for the application of biocatalysis at an industrial scale. Recently, the possibility of using the photosystem of cyanobacteria to supply high amounts of reduced nicotinamide to a recombinant enoate reductase opened a new strategy for overcoming this hurdle. This paper presents the expansion of the photosynthetic regeneration system to a Baeyer–Villiger monooxygenase. Despite the potential of this strategy, this work also presents some of the encountered challenges as well as possible solutions, which will require further investigation. The successful enzymatic oxygenation shows that cyanobacterial whole-cell biocatalysis is an applicable approach that allows fuelling selective oxyfunctionalisation reactions at the expense of light and water. Yet, several hurdles such as side-reactions and the cell-density limitation, probably due to self-shading of the cells, will have to be overcome on the way to synthetic applications. Full article
(This article belongs to the Special Issue Water Oxidation Catalysis)
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Open AccessArticle Improved H2 Production by Ethanol Steam Reforming over Sc2O3-Doped Co-ZnO Catalysts
Catalysts 2017, 7(8), 241; doi:10.3390/catal7080241
Received: 2 July 2017 / Revised: 15 August 2017 / Accepted: 16 August 2017 / Published: 18 August 2017
Cited by 1 | PDF Full-text (2518 KB) | HTML Full-text | XML Full-text
Abstract
H2 production by catalytically ethanol steam reforming (ESR) is an effective and prospective method for the application of fuel cells. However, the catalysts’ desirable activity and stability remains an unprecedented challenge. Herein, a type of Sc2O3-doped Co-ZnO catalyst
[...] Read more.
H2 production by catalytically ethanol steam reforming (ESR) is an effective and prospective method for the application of fuel cells. However, the catalysts’ desirable activity and stability remains an unprecedented challenge. Herein, a type of Sc2O3-doped Co-ZnO catalyst was developed by a co-precipitation method. The so-constructed Co2Zn1Sc0.3 catalyst exhibited a superb catalytic performance compared with Co-ZnO, giving a STY(H2) as high as 1.099 mol·h−1·g-cat−1 (data taken 100 h after the reaction started). In comparison, the pristine Co-ZnO catalyst only afforded a STY(H2) of 0.684 mol·h−1·g-cat−1 under identical reaction conditions. Characterization results revealed that the Sc2O3 dopant strengthened the electronic interaction between Co species and ZnO, which was in favour of elevating the reduction temperature of Co oxides and boosting the dispersion of the Con+ (n = 1 or 2). The introduction of Sc2O3 induced the formation of O2− and OH. All of these effects effectively inhibited the sintering of active Co species and markedly improved the activity and operating stability of the catalyst. Full article
(This article belongs to the Special Issue Reforming Catalysts)
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Open AccessArticle Galactooligosaccharide Production from Pantoea anthophila Strains Isolated from “Tejuino”, a Mexican Traditional Fermented Beverage
Catalysts 2017, 7(8), 242; doi:10.3390/catal7080242
Received: 2 August 2017 / Revised: 15 August 2017 / Accepted: 16 August 2017 / Published: 22 August 2017
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Abstract
Two Pantoea anthophila bacterial strains were isolated from “tejuino”, a traditional Mexican beverage, and studied as β-galactosidase producers for galactooligosaccharides synthesis. Using 400 g/L of lactose, 50 °C, and 15 U/mL of β-galactosidase activity with ethanol-permeabilized cells, the maximum galactooligosaccharides (GOS) yield determined
[...] Read more.
Two Pantoea anthophila bacterial strains were isolated from “tejuino”, a traditional Mexican beverage, and studied as β-galactosidase producers for galactooligosaccharides synthesis. Using 400 g/L of lactose, 50 °C, and 15 U/mL of β-galactosidase activity with ethanol-permeabilized cells, the maximum galactooligosaccharides (GOS) yield determined by High performance anion exchange chromatography with pulse amperometric detection (HPAEC-PAD) was 136 g/L (34% w/w of total sugars) at 96% of lactose conversion for Bac 55.2 and 145 g/L (36% w/w of total sugars) at 94% of lactose conversion for Bac 69.1. The main synthesized products were the disaccharides allolactose [Gal-β(1 → 6)-Glc] and 6-galactobiose [Gal-β(1 → 6)-Gal], as well as the trisaccharides 3′-galactosyl-lactose [Gal-β(1 → 3)-Gal-β(1 → 4)-Glc], 6-galactotriose [Gal-β(1 → 6)-Gal-β(1 → 6)-Gal], 3′-galactosyl-allolactose [Gal-β(1 → 3)-Gal-β(1 → 6)-Glc], and 6′-galactosyl-lactose [Gal-β(1 → 6)-Gal-β(1 → 4)-Glc]. The β-galactosidases present in both strains showed a high transgalactosylation activity and formed principally β(1 → 3) and β(1 → 6) linkages. Considering the stability and bifidogenic properties of GOS containing such types of bonds, P. anthophila strains Bac 55.2 and Bac 69.1 possess a high potential as novel biocatalysts for prebiotic industrial production. Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
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Open AccessArticle Synthesis of NaOH-Modified TiOF2 and Its Enhanced Visible Light Photocatalytic Performance on RhB
Catalysts 2017, 7(8), 243; doi:10.3390/catal7080243
Received: 16 July 2017 / Revised: 7 August 2017 / Accepted: 16 August 2017 / Published: 22 August 2017
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Abstract
NaOH-modified TiOF2 was successfully prepared using a modified low-temperature hydrothermal method. Scanning electron microscopy shows that NaOH-modified TiOF2 displayed a complex network shape with network units of about 100 nm. The structures of NaOH-modified TiOF2 have not been reported elsewhere.
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NaOH-modified TiOF2 was successfully prepared using a modified low-temperature hydrothermal method. Scanning electron microscopy shows that NaOH-modified TiOF2 displayed a complex network shape with network units of about 100 nm. The structures of NaOH-modified TiOF2 have not been reported elsewhere. The network shape permits the NaOH-modified TiOF2 a SBET of 36 m2∙g−1 and a pore diameter around 49 nm. X-ray diffraction characterization shows that TiOF2 and NaOH-modified TiOF2 are crystallized with a pure changed cubic phase which accords with the SEM results. Fourier transform infrared spectroscopy characterization shows that NaOH-modified TiOF2 has more O–H groups to supply more lone electron pairs to transfer from O of O–H to Ti and O of TiOF2. UV–vis diffuse reflectance spectroscopy (DRS) shows that the NaOH-modified TiOF2 sample has an adsorption plateau rising from 400 to 600 nm in comparison with TiOF2, and its band gap is 2.62 eV, lower than that of TiOF2. Due to the lower band gap, more O–H groups adsorption, network morphologies with larger surface area, and sensitization progress, the NaOH-modified TiOF2 exhibited much higher photocatalytic activity for Rhodamine B (RhB) degradation. In addition, considering the sensitization progress, O–H groups on TiOF2 not only accelerated the degradation rate of RhB, but also changed its degradation path. As a result, the NaOH-modified TiOF2 exhibited much higher photocatalytic activity for RhB degradation than the TiOF2 in references under visible light. This finding provides a new idea to enhance the photocatalytic performance by NaOH modification of the surface of TiOF2. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessReview Photocatalytic Membrane Reactors (PMRs) in Water Treatment: Configurations and Influencing Factors
Catalysts 2017, 7(8), 224; doi:10.3390/catal7080224
Received: 7 June 2017 / Revised: 14 July 2017 / Accepted: 17 July 2017 / Published: 25 July 2017
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Abstract
The lack of access to clean water remains a severe issue all over the world. Coupling photocatalysis with the membrane separation process, which is known as a photocatalytic membrane reactor (PMR), is promising for water treatment. PMR has developed rapidly during the last
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The lack of access to clean water remains a severe issue all over the world. Coupling photocatalysis with the membrane separation process, which is known as a photocatalytic membrane reactor (PMR), is promising for water treatment. PMR has developed rapidly during the last few years, and this paper presents an overview of the progress in the configuration and operational parameters of PMRs. Two main configurations of PMRs (PMRs with immobilized photocatalyst; PMRs with suspended photocatalyst) are comprehensively described and characterized. Various influencing factors on the performance of PMRs, including photocatalyst, light source, water quality, aeration and membrane, are detailed. Moreover, a discussion on the current problems and development prospects of PMRs for practical application are presented. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors)
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Open AccessFeature PaperReview Recent Progress on the Synthesis of Graphene-Based Nanostructures as Counter Electrodes in DSSCs Based on Iodine/Iodide Electrolytes
Catalysts 2017, 7(8), 234; doi:10.3390/catal7080234
Received: 27 July 2017 / Revised: 9 August 2017 / Accepted: 9 August 2017 / Published: 14 August 2017
PDF Full-text (2829 KB) | HTML Full-text | XML Full-text
Abstract
Graphene-based nanomaterials functionalized by different doping strategies have attracted great attention for energy conversion themes, due to their large specific surface area, high conductivity, and appreciable electrocatalytic properties. This mini-review presents an overview of the recent progress in the synthesis of graphene-based nanomaterials
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Graphene-based nanomaterials functionalized by different doping strategies have attracted great attention for energy conversion themes, due to their large specific surface area, high conductivity, and appreciable electrocatalytic properties. This mini-review presents an overview of the recent progress in the synthesis of graphene-based nanomaterials as counter electrodes for dye-sensitized solar cells based on iodine/iodide electrolytes, along with challenges and perspectives in this exciting field. Full article
(This article belongs to the Special Issue Graphene-Based Materials for Energy Conversion)
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