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Catalysts, Volume 7, Issue 11 (November 2017)

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Cover Story (view full-size image) Fine chemistry products such as agro-chemicals or pharmaceuticals require ketones and/or aldehydes [...] Read more.
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Open AccessArticle Polyelectrolyte Complex Beads by Novel Two-Step Process for Improved Performance of Viable Whole-Cell Baeyer-Villiger Monoxygenase by Immobilization
Catalysts 2017, 7(11), 353; https://doi.org/10.3390/catal7110353
Received: 18 October 2017 / Revised: 10 November 2017 / Accepted: 13 November 2017 / Published: 21 November 2017
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Abstract
A novel immobilization matrix for the entrapment of viable whole-cell Baeyer–Villiger monooxygenase was developed. Viable recombinant Escherichia coli cells overexpressing cyclohexanone monooxygenase were entrapped in polyelectrolyte complex beads prepared by a two-step reaction of oppositely-charged polymers including highly defined cellulose sulphate. Immobilized cells
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A novel immobilization matrix for the entrapment of viable whole-cell Baeyer–Villiger monooxygenase was developed. Viable recombinant Escherichia coli cells overexpressing cyclohexanone monooxygenase were entrapped in polyelectrolyte complex beads prepared by a two-step reaction of oppositely-charged polymers including highly defined cellulose sulphate. Immobilized cells exhibited higher operational stability than free cells during 10 repeated cycles of Baeyer–Villiger biooxidations of rac-bicyclo[3.2.0]hept-2-en-6-one to the corresponding lactones (1R,5S)-3-oxabicyclo-[3.3.0]oct-6-en-3-one and (1S,5R)-2-oxabicyclo-[3.3.0]oct-6-en-3-one. The morphology of polyelectrolyte complex beads was characterised by environmental scanning electron microscopy; the spatial distribution of polymers in the beads and cell viability were examined using confocal laser scanning microscopy, and the texture was characterised by the mechanical resistance measurements. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessFeature PaperReview Advances in Base-Free Oxidation of Bio-Based Compounds on Supported Gold Catalysts
Catalysts 2017, 7(11), 352; https://doi.org/10.3390/catal7110352
Received: 19 September 2017 / Revised: 10 November 2017 / Accepted: 15 November 2017 / Published: 21 November 2017
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Abstract
The oxidation of bio-based molecules in general, and of carbohydrates and furanics in particular, is a highly attractive process. The catalytic conversion of renewable compounds is of high importance. Acids and other chemical intermediates issued from oxidation processes have many applications related, especially,
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The oxidation of bio-based molecules in general, and of carbohydrates and furanics in particular, is a highly attractive process. The catalytic conversion of renewable compounds is of high importance. Acids and other chemical intermediates issued from oxidation processes have many applications related, especially, to food and detergents, as well as to pharmaceutics, cosmetics, and the chemical industry. Until now, the oxidation of sugars, furfural, or 5-hydroxymethylfurfural has been mainly conducted through biochemical processes or with strong inorganic oxidants. The use of these processes very often presents many disadvantages, especially regarding products separation and selectivity control. Generally, the oxidation is performed in batch conditions using an appropriate catalyst and a basic aqueous solution (pH 7–9), while bubbling oxygen or air through the slurry. However, there is a renewed interest in working in base-free conditions to avoid the production of salts. Actually, this gives direct access to different acids or diacids without laborious product purification steps. This review focuses on processes applying gold-based catalysts, and on the catalytic properties of these systems in the base-free oxidation of important compounds: C5–C6 sugars, furfural, and 5-hydroxymethylfurfural. A better understanding of the chemical and physical properties of the catalysts and of the operating conditions applied in the oxidation reactions is essential. For this reason, in this review we put emphasis on these most impacting factors. Full article
(This article belongs to the Special Issue Catalytic Sustainable Processes in Biorefineries)
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Open AccessArticle Facile One-Pot Synthesis of Amidoalkyl Naphthols and Benzopyrans Using Magnetic Nanoparticle-Supported Acidic Ionic Liquid as a Highly Efficient and Reusable Catalyst
Catalysts 2017, 7(11), 351; https://doi.org/10.3390/catal7110351
Received: 30 October 2017 / Revised: 10 November 2017 / Accepted: 17 November 2017 / Published: 21 November 2017
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Abstract
An efficient and eco-friendly procedure for the synthesis of 1-amidoalkyl-2-naphthol and tetrahydrobenzo[b]pyran derivatives has been developed through a one-pot three-component condensation of aldehydes with 2-naphthol and amides, or with malononitrile and dimedone in the presence of magnetic nanoparticle supported acidic ionic
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An efficient and eco-friendly procedure for the synthesis of 1-amidoalkyl-2-naphthol and tetrahydrobenzo[b]pyran derivatives has been developed through a one-pot three-component condensation of aldehydes with 2-naphthol and amides, or with malononitrile and dimedone in the presence of magnetic nanoparticle supported acidic ionic liquid (AIL@MNP) as a novel heterogeneous catalyst under solvent-free conditions. This new procedure offers several advantages such as short reaction time, excellent yields, operational simplicity and without any tedious work-up for catalyst recovery or product purification. Moreover, the catalyst could be simply separated by an external magnet and reused six times without significant loss of catalytic activity. Full article
(This article belongs to the Special Issue Organocatalysis in Ionic Liquids)
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Open AccessArticle Characteristics of NixFe1−xOy Electrocatalyst on Hematite as Photoanode for Solar Hydrogen Production
Catalysts 2017, 7(11), 350; https://doi.org/10.3390/catal7110350
Received: 20 September 2017 / Revised: 15 November 2017 / Accepted: 17 November 2017 / Published: 20 November 2017
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Abstract
The use of hematite as the photoanode for photoelectrochemical hydrogen production by solar energy has been actively studied due to its abundance, stability, and adequate optical properties. Deposition of an electrocatalyst overlayer on the hematite may increase kinetics and lower the onset potential
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The use of hematite as the photoanode for photoelectrochemical hydrogen production by solar energy has been actively studied due to its abundance, stability, and adequate optical properties. Deposition of an electrocatalyst overlayer on the hematite may increase kinetics and lower the onset potential for water splitting. NixFe1−xOy is one of the most effective electrocatalysts reported for this purpose. However, the condition and results of the previous reports vary significantly, and a comprehensive model for NixFe1−xOy/hematite is lacking. Here, we report a simple and novel chemical bath deposition method for depositing low-onset-potential NixFe1−xOy electrocatalyst on hematite. With a Ni percentage of 80% and an immersion time of 2 min, the as-prepared NixFe1−xOy overlayer raised the photovoltage from 0.2 V to 0.7 V, leading to a cathodic shift of the onset potential by 400 mV, while maintaining the same level of current density. The dependence of the electrochemical and photoelectrochemical characteristics of the photoanode on the condition of the electrocatalyst was studied systematically and explained based on energy level diagrams and kinetics. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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Open AccessArticle Synergistic Enhancement in Catalytic Performance of Superparamagnetic Fe3O4@Bacilus subtilis as Recyclable Fenton-Like Catalyst
Catalysts 2017, 7(11), 349; https://doi.org/10.3390/catal7110349
Received: 27 August 2017 / Revised: 2 October 2017 / Accepted: 3 October 2017 / Published: 20 November 2017
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Abstract
Novel well-defined superparamagnetic Fe3O4@Bacilus subtilis composite (Fe3O4@B. subtilis SPMC) was synthesized through a facile electrostatic attraction method and used as a recyclable heterogeneous Fenton-like catalyst. With the presence of H2O2
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Novel well-defined superparamagnetic Fe3O4@Bacilus subtilis composite (Fe3O4@B. subtilis SPMC) was synthesized through a facile electrostatic attraction method and used as a recyclable heterogeneous Fenton-like catalyst. With the presence of H2O2, Fe3O4@B. subtilis SPMC can remove nearly 87% of the doxycycline at the initial concentration of 50 mg L−1, exhibiting enhanced Fenton-like catalytic performance than pristine Fe3O4. The mechanism study demonstrates the synergistic effect between Bacilus subtilis adsorption and Fenton-like ability of Fe3O4 dominates the enhancement for Fenton-like catalytic efficiency of Fe3O4@B. subtilis SPMC. The obtained composite shows excellent recycling ability, reusability, and stability, which pave a new way for future design on highly efficient Fenton-like catalyst for degradation of organic pollutants. Full article
(This article belongs to the Special Issue Magnetic Nanocatalysts)
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Open AccessFeature PaperArticle Dehydrogenation of Formic Acid over a Homogeneous Ru-TPPTS Catalyst: Unwanted CO Production and Its Successful Removal by PROX
Catalysts 2017, 7(11), 348; https://doi.org/10.3390/catal7110348
Received: 26 October 2017 / Revised: 13 November 2017 / Accepted: 13 November 2017 / Published: 20 November 2017
Cited by 2 | PDF Full-text (2286 KB) | HTML Full-text | XML Full-text
Abstract
Formic acid (FA) is considered as a potential durable energy carrier. It contains ~4.4 wt % of hydrogen (or 53 g/L) which can be catalytically released and converted to electricity using a proton exchange membrane (PEM) fuel cell. Although various catalysts have been
[...] Read more.
Formic acid (FA) is considered as a potential durable energy carrier. It contains ~4.4 wt % of hydrogen (or 53 g/L) which can be catalytically released and converted to electricity using a proton exchange membrane (PEM) fuel cell. Although various catalysts have been reported to be very selective towards FA dehydrogenation (resulting in H2 and CO2), a side-production of CO and H2O (FA dehydration) should also be considered, because most PEM hydrogen fuel cells are poisoned by CO. In this research, a highly active aqueous catalytic system containing Ru(III) chloride and meta-trisulfonated triphenylphosphine (mTPPTS) as a ligand was applied for FA dehydrogenation in a continuous mode. CO concentration (8–70 ppm) in the resulting H2 + CO2 gas stream was measured using a wide range of reactor operating conditions. The CO concentration was found to be independent on the reactor temperature but increased with increasing FA feed. It was concluded that unwanted CO concentration in the H2 + CO2 gas stream was dependent on the current FA concentration in the reactor which was in turn dependent on the reaction design. Next, preferential oxidation (PROX) on a Pt/Al2O3 catalyst was applied to remove CO traces from the H2 + CO2 stream. It was demonstrated that CO concentration in the stream could be reduced to a level tolerable for PEM fuel cells (~3 ppm). Full article
(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)
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Open AccessFeature PaperReview On the Structure of Chiral Dirhodium(II) Carboxylate Catalysts: Stereoselectivity Relevance and Insights
Catalysts 2017, 7(11), 347; https://doi.org/10.3390/catal7110347
Received: 2 November 2017 / Revised: 14 November 2017 / Accepted: 17 November 2017 / Published: 20 November 2017
Cited by 1 | PDF Full-text (4126 KB) | HTML Full-text | XML Full-text
Abstract
Modern experiments have offered alternative interpretations on the symmetry of chiral dirhodium(II) carboxylate complexes and its relationship to their level of enantioselectivity. So, this contribution is to provide an insight on how the knowledge around the structure of these catalysts has evolved with
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Modern experiments have offered alternative interpretations on the symmetry of chiral dirhodium(II) carboxylate complexes and its relationship to their level of enantioselectivity. So, this contribution is to provide an insight on how the knowledge around the structure of these catalysts has evolved with a particular emphasis on the impact of this knowledge on enantioselectivity prediction and catalyst design. Full article
(This article belongs to the Special Issue Asymmetric Catalysis in Organic Synthesis)
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Open AccessArticle Efficient Degradation of Refractory Organics Using Sulfate Radicals Generated Directly from WO3 Photoelectrode and the Catalytic Reaction of Sulfate
Catalysts 2017, 7(11), 346; https://doi.org/10.3390/catal7110346
Received: 12 October 2017 / Revised: 10 November 2017 / Accepted: 12 November 2017 / Published: 17 November 2017
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Abstract
An environment-friendly method of efficiently degrading refractory organics using SO4• generated directly from a WO3 photoelectrode and a catalytic reaction of sulfate was proposed, in which the cycling process of SO42− → SO4• →
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An environment-friendly method of efficiently degrading refractory organics using SO4• generated directly from a WO3 photoelectrode and a catalytic reaction of sulfate was proposed, in which the cycling process of SO42− → SO4• → SO42− was achieved in the treatment of organic pollutants without any other activator and without the continuous addition of sulfate. The results show that the removal efficiency for a typical refractory organics of methyl orange (MO) with 5 mg/L was up to 95% within 80 min, and merely 3% by photolysis and 19% by photocatalysis, respectively, under similar conditions. The rate constant for the disposal of MO at pH 2, in which SO4• instead of HO• is the main oxidizer confirmed by radical scavenger experiment, is up to 5.21 × 10−4 s−1, which was ~6.6 times that (7.89 × 10−5 s−1) under neutral condition, in which HO• is the main oxidizer. The concentration of active persulfate (S2O82−, SO52−, and SO4•) species at pH 2 was up to 0.38 mM, which was ~16-fold as much as that (0.023 mM) in neutral conditions. The method provides a new approach for the treatment and resource utilization of sulfate wastewater. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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Open AccessReview Base Catalysis by Mono- and Polyoxometalates
Catalysts 2017, 7(11), 345; https://doi.org/10.3390/catal7110345
Received: 17 October 2017 / Revised: 9 November 2017 / Accepted: 13 November 2017 / Published: 16 November 2017
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Abstract
In sharp contrast with acid-, photo-, and oxidation-catalysis by polyoxometalates, base catalysis by polyoxometalates has scarcely been investigated. The use of polyoxometalates as base catalysts have very recently received much attention and has been extensively investigated. Numerous mono- and polyoxometalate base catalyst systems
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In sharp contrast with acid-, photo-, and oxidation-catalysis by polyoxometalates, base catalysis by polyoxometalates has scarcely been investigated. The use of polyoxometalates as base catalysts have very recently received much attention and has been extensively investigated. Numerous mono- and polyoxometalate base catalyst systems effective for the chemical fixation of CO2, cyanosilylation of carbonyl compounds, and C–C bond forming reactions have been developed. Mono- and polyoxometalate base catalysts are classified into four main groups with respect to their structures: (a) monomeric metalates; (b) isopolyoxometalates; (c) heteropolyoxometalates; and (d) transition-metal-substituted polyoxometalates. This review article focuses on the relationship among the molecular structures, the basic properties, and the unique base catalysis of polyoxometalates on the basis of groups (a)–(d). In addition, reaction mechanisms including the specific activation of substrates and/or reagents such as the abstraction of protons, nucleophilic action toward substrates, and bifunctional action in combination with metal catalysts are comprehensively summarized. Full article
(This article belongs to the Special Issue Recent Advances in Polyoxometalate-Catalyzed Reactions)
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Open AccessReview Ultrasonic Monitoring of Biocatalysis in Solutions and Complex Dispersions
Catalysts 2017, 7(11), 336; https://doi.org/10.3390/catal7110336
Received: 19 September 2017 / Revised: 26 October 2017 / Accepted: 26 October 2017 / Published: 15 November 2017
Cited by 1 | PDF Full-text (8212 KB) | HTML Full-text | XML Full-text
Abstract
The rapidly growing field of chemical catalysis is dependent on analytical methods for non-destructive real-time monitoring of chemical reactions in complex systems such as emulsions, suspensions and gels, where most analytical techniques are limited in their applicability, especially if the media is opaque,
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The rapidly growing field of chemical catalysis is dependent on analytical methods for non-destructive real-time monitoring of chemical reactions in complex systems such as emulsions, suspensions and gels, where most analytical techniques are limited in their applicability, especially if the media is opaque, or if the reactants/products do not possess optical activity. High-resolution ultrasonic spectroscopy is one of the novel technologies based on measurements of parameters of ultrasonic waves propagating through analyzed samples, which can be utilized for real-time non-invasive monitoring of chemical reactions. It does not require optical transparency, optical markers and is applicable for monitoring of reactions in continuous media and in micro/nano bioreactors (e.g., nanodroplets of microemulsions). The technology enables measurements of concentrations of substrates and products over the whole course of reaction, analysis of time profiles of the degree of polymerization and molar mass of polymers and oligomers, evolutions of reaction rates, evaluation of kinetic mechanisms, measurements of kinetic and equilibrium constants and reaction Gibbs energy. It also provides tools for assessments of various aspects of performance of catalysts/enzymes including inhibition effects, reversible and irreversible thermal deactivation. In addition, ultrasonic scattering effects in dispersions allow real-time monitoring of structural changes in the medium accompanying chemical reactions. Full article
(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)
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Open AccessArticle Fe-Doped TiO2 Supported on HY Zeolite for Solar Photocatalytic Treatment of Dye Pollutants
Catalysts 2017, 7(11), 344; https://doi.org/10.3390/catal7110344
Received: 24 October 2017 / Revised: 9 November 2017 / Accepted: 10 November 2017 / Published: 14 November 2017
Cited by 1 | PDF Full-text (2932 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Zeolite-supported TiO2 and Fe-doped TiO2/zeolite photocatalysts were synthesized, aiming at improving the adsorption properties of the microporous support towards polluting dyes and the photocatalytic performance of TiO2 in the treatment of the adsorbed organics. The TiO2/HY zeolite
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Zeolite-supported TiO2 and Fe-doped TiO2/zeolite photocatalysts were synthesized, aiming at improving the adsorption properties of the microporous support towards polluting dyes and the photocatalytic performance of TiO2 in the treatment of the adsorbed organics. The TiO2/HY zeolite catalyst exhibited the best performance in the photocatalytic degradation of methylene blue, MB, over 10 wt% TiO2/HY under UV light at 254 nm. The addition of Fe species in the synthesis mixture led to Fe-TiO2/HY catalyst. The combination of adequate zeolite, good titanium dioxide dispersion, and Fe doping led to a remarkable performance in the degradation of the model dye. Over a 10 wt% Fe-doped TiO2/HY catalyst a total removal of MB (>98%) was achieved after 60 min under very mild conditions and simple visible light irradiation. Full article
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Open AccessArticle Fine-Tuning Synthesis and Characterization of Mono-Sized H-Beta Zeolite-Supported Palladium-Iridium Nanoparticles and Application in the Selective Hydrogenation of Acetylene
Catalysts 2017, 7(11), 343; https://doi.org/10.3390/catal7110343
Received: 1 October 2017 / Revised: 28 October 2017 / Accepted: 29 October 2017 / Published: 13 November 2017
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Abstract
In this research, a mono-sized Beta zeolite support synthesized by the solvothermal method was used in the selective acetylene to ethylene hydrogenation reaction with minimum coke build up on the catalyst surface. Tetrapropylammonium hydroxide (TPAOH), tetrapropylammonium bromide (TPABr), n-butylamine, and morpholine were
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In this research, a mono-sized Beta zeolite support synthesized by the solvothermal method was used in the selective acetylene to ethylene hydrogenation reaction with minimum coke build up on the catalyst surface. Tetrapropylammonium hydroxide (TPAOH), tetrapropylammonium bromide (TPABr), n-butylamine, and morpholine were used as structure direct agents (SDA) in the support to obtain various shapes. The characterization results show that although the Si/(Al+SDA) ratio has no effect on the phase purity of support, it has a remarkable effect on porosity, crystal size, shape, and structure of micropores. After comparing characterization results, the developed support, based on TPAOH, was selected and modified by different metals (Ce, Ir, Ag, and Pd) using the incipient wetness co-impregnation method. Since there is an interaction between selectivity and conversion, the optimum metal content in the synthesized catalysts and reaction condition were determined to achieve the desired acetylene conversion and ethylene selectivity. The physicochemical transformation of the developed optimum catalysts was determined using different techniques. Based on the characterization and cata-test results, the catalyst which contains 0.29% Ir and 0.08% Pd presents a better performance and higher stability compared to the other catalysts due to the moderate size and mono layer dispersion of the metals on the support. The experimental results show that acetylene conversion and ethylene selectivity approach 97% and 92% at 55 °C, respectively. Full article
(This article belongs to the Special Issue Zeolites and Catalysis)
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Open AccessArticle Green Synthesis of Ultraviolet Absorber 2-Ethylhexyl Salicylate: Experimental Design and Artificial Neural Network Modeling
Catalysts 2017, 7(11), 342; https://doi.org/10.3390/catal7110342
Received: 21 October 2017 / Revised: 3 November 2017 / Accepted: 10 November 2017 / Published: 13 November 2017
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Abstract
2-Ethylhexyl salicylate, an ultraviolet filter, is widely used to protect skin against sunlight-induced harmful effects in the cosmetic industry. In this study, the green synthesis of 2-ethylhexyl salicylate using immobilized lipase through a solvent-free and reduced pressure evaporation system was investigated. A Box–Behnken
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2-Ethylhexyl salicylate, an ultraviolet filter, is widely used to protect skin against sunlight-induced harmful effects in the cosmetic industry. In this study, the green synthesis of 2-ethylhexyl salicylate using immobilized lipase through a solvent-free and reduced pressure evaporation system was investigated. A Box–Behnken design was employed to develop an artificial neural network (ANN) model. The parameters for an optimal architecture of an ANN were set out: a quick propagation algorithm, a hyperbolic tangent transfer function, 10,000 iterations, and six nodes within the hidden layer. The best-fitting performance of the ANN was determined by the coefficient of determination and the root-mean-square error between the correlation of predicted and experimental data, indicating that the ANN displayed excellent data-fitting properties. Finally, the experimental conditions of synthesis were well established with the optimal parameters to obtain a high conversion of 2-ethylhexyl salicylate. In conclusion, this study efficiently replaces the traditional solvents with a green process for the synthesis of 2-ethylhexyl salicylate to avoid environmental contamination, and this process is well-modeled by a methodological ANN for optimization, which might be a benefit for industrial production. Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
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Open AccessReview Heterogeneous Catalysis on Metal Oxides
Catalysts 2017, 7(11), 341; https://doi.org/10.3390/catal7110341
Received: 8 October 2017 / Revised: 25 October 2017 / Accepted: 27 October 2017 / Published: 10 November 2017
Cited by 2 | PDF Full-text (4487 KB) | HTML Full-text | XML Full-text
Abstract
This review article contains a reminder of the fundamentals of heterogeneous catalysis and a description of the main domains of heterogeneous catalysis and main families of metal oxide catalysts, which cover acid-base reactions, selective partial oxidation reactions, total oxidation reactions, depollution, biomass conversion,
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This review article contains a reminder of the fundamentals of heterogeneous catalysis and a description of the main domains of heterogeneous catalysis and main families of metal oxide catalysts, which cover acid-base reactions, selective partial oxidation reactions, total oxidation reactions, depollution, biomass conversion, green chemistry and photocatalysis. Metal oxide catalysts are essential components in most refining and petrochemical processes. These catalysts are also critical to improving environmental quality. This paper attempts to review the major current industrial applications of supported and unsupported metal oxide catalysts. Viewpoints for understanding the catalysts’ action are given, while applications and several case studies from academia and industry are given. Emphases are on catalyst description from synthesis to reaction conditions, on main industrial applications in the different domains and on views for the future, mainly regulated by environmental issues. Following a review of the major types of metal oxide catalysts and the processes that use these catalysts, this paper considers current and prospective major applications, where recent advances in the science of metal oxide catalysts have major economic and environmental impacts. Full article
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Open AccessArticle YCl3-Catalyzed Highly Selective Ring Opening of Epoxides by Amines at Room Temperature and under Solvent-Free Conditions
Catalysts 2017, 7(11), 340; https://doi.org/10.3390/catal7110340
Received: 16 October 2017 / Revised: 29 October 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
Cited by 1 | PDF Full-text (6277 KB) | HTML Full-text | XML Full-text
Abstract
A simple, efficient, and environmentally benign approach for the synthesis of β-amino alcohols is herein described. YCl3 efficiently carried out the ring opening of epoxides by amines to produce β-amino alcohols under solvent-free conditions at room temperature. This catalytic approach is very
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A simple, efficient, and environmentally benign approach for the synthesis of β-amino alcohols is herein described. YCl3 efficiently carried out the ring opening of epoxides by amines to produce β-amino alcohols under solvent-free conditions at room temperature. This catalytic approach is very effective, with several aromatic and aliphatic oxiranes and amines. A mere 1 mol % concentration of YCl3 is enough to deliver β-amino alcohols in good to excellent yields with high regioselectivity. Full article
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