Open AccessArticle
l-Amino Acid Production by a Immobilized Double-Racemase Hydantoinase Process: Improvement and Comparison with a Free Protein System
Catalysts 2017, 7(6), 192; doi:10.3390/catal7060192 -
Abstract
Protein immobilization is proving to be an environmentally friendly strategy for manufacturing biochemicals at high yields and low production costs. This work describes the optimization of the so-called “double-racemase hydantoinase process,” a system of four enzymes used to produce optically pure l-amino
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Protein immobilization is proving to be an environmentally friendly strategy for manufacturing biochemicals at high yields and low production costs. This work describes the optimization of the so-called “double-racemase hydantoinase process,” a system of four enzymes used to produce optically pure l-amino acids from a racemic mixture of hydantoins. The four proteins were immobilized separately, and, based on their specific activity, the optimal whole relation was determined. The first enzyme, d,l-hydantoinase, preferably hydrolyzes d-hydantoins from d,l-hydantoins to N-carbamoyl-d-amino acids. The remaining l-hydantoins are racemized by the second enzyme, hydantoin racemase, and continue supplying substrate d-hydantoins to the first enzyme. N-carbamoyl-d-amino acid is racemized in turn to N-carbamoyl-l-amino acid by the third enzyme, carbamoyl racemase. Finally, the N-carbamoyl-l-amino acid is transformed to l-amino acid by the fourth enzyme, l-carbamoylase. Therefore, the product of one enzyme is the substrate of another. Perfect coordination of the four activities is necessary to avoid the accumulation of reaction intermediates and to achieve an adequate rate for commercial purposes. The system has shown a broad pH optimum of 7–9, with a maximum activity at 8 and an optimal temperature of 60 °C. Comparison of the immobilized system with the free protein system showed that the reaction velocity increased for the production of norvaline, norleucine, ABA, and homophenylalanine, while it decreased for l-valine and remained unchanged for l-methionine. Full article
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Open AccessReview
Zirconium Phosphate Catalysts in the XXI Century: State of the Art from 2010 to Date
Catalysts 2017, 7(6), 190; doi:10.3390/catal7060190 -
Abstract
An overview on the developments of zirconium phosphate (ZrP) and its organic derivatives in heterogeneous catalysis in recent years is reported in the present review. Two basic aspects have been emphasized: first, the catalytic properties of zirconium phosphates were discussed, with particular attention
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An overview on the developments of zirconium phosphate (ZrP) and its organic derivatives in heterogeneous catalysis in recent years is reported in the present review. Two basic aspects have been emphasized: first, the catalytic properties of zirconium phosphates were discussed, with particular attention to the effect of surface acidity and hydrophobic/hydrophilic character, textural properties, and particle morphology on the catalytic performances. Then, the use of zirconium phosphates as support for catalytic active species was reported, including organometallic complexes, metal ions, noble metal, and metal oxide nanoparticles. Zirconium phosphate plays, in those cases, a dual role, since it promotes the dispersion and stabilization of the catalysts, thanks to their interaction with the active sites on the surface of ZrP, and facilitates the recovery and reuse of the catalytic species due to their immobilization on the solid support. Full article
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Open AccessArticle
A Theoretical Insight into Enhanced Catalytic Activity of Au by Multiple Twin Nanoparticles
Catalysts 2017, 7(6), 191; doi:10.3390/catal7060191 -
Abstract
Recently, it has been reported that the morphology of Au nanoparticles (NPs) affects the catalytic activity of CO oxidation; twin crystal NPs show higher activity for CO oxidation than single-crystal NPs. In this study, density functional calculations have been carried out to investigate
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Recently, it has been reported that the morphology of Au nanoparticles (NPs) affects the catalytic activity of CO oxidation; twin crystal NPs show higher activity for CO oxidation than single-crystal NPs. In this study, density functional calculations have been carried out to investigate the morphology effect of Au NPs using CO as a probe molecule. In the case of Au NPs with a size of more than 2 nm, CO adsorption energy on the Au NPs is mainly determined by a coordination number (CN) of adsorption sites. CO binding to a multiple twin NP with a size of about 1 nm is stronger than that on a single-crystal NP with the same size. A simple CN explanation cannot be applied to the enhancement of CO binding to the small multiple twin NP. This enhancement is related to a deformation of the NP structure before and after CO adsorption. It is suggested that the multiple twin NP with a size of less than 1 nm, which shows the deformation upon CO adsorption, contributes to the higher activity for CO oxidation. Full article
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Open AccessArticle
Co3O4 Nanoparticle-Decorated N-Doped Mesoporous Carbon Nanofibers as an Efficient Catalyst for Oxygen Reduction Reaction
Catalysts 2017, 7(6), 189; doi:10.3390/catal7060189 -
Abstract
A low cost, durable, and efficient electrocatalyst for oxygen reduction reactions (ORR) is essential for high-performance fuel cells. Here, we fabricated Co3O4 nanoparticles (NPs) anchored on N-doped mesoporous carbon nanofibers (Co3O4/NMCF) by electrospinning combined with the
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A low cost, durable, and efficient electrocatalyst for oxygen reduction reactions (ORR) is essential for high-performance fuel cells. Here, we fabricated Co3O4 nanoparticles (NPs) anchored on N-doped mesoporous carbon nanofibers (Co3O4/NMCF) by electrospinning combined with the simple heat treatment. Within this composite, carbon nanofibers possess a mesoporous structure, contributed to obtain a high surface area, which can facilitate the infiltration of electrolyte. Moreover, this one-dimensional (1D) carbon nanofiber also acts as a 1D conductive channel, effectively improving the transmission of electrons. In addition, the doping of the N element with high content combined with homogenously distributed Co3O4 NPs can significantly enhance the ORR electrocatalytic activity. Benefiting from the advantages of material and structure, the Co3O4/NMCF catalyst favors a four electron transfer process in alkaline media, exhibiting good ORR electrocatalytic activity, and its durability is much better than that of commercial Pt/C. Full article
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Open AccessArticle
Using Laccases in the Nanoflower to Synthesize Viniferin
Catalysts 2017, 7(6), 188; doi:10.3390/catal7060188 -
Abstract
The laccase-incorporated nanoflower was fabricated and characterized by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). SEM images indicate that the laccase-incorporated nanoflower has a high surface area, which may facilitate the mass transfer of the substrate and the product. FTIR
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The laccase-incorporated nanoflower was fabricated and characterized by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). SEM images indicate that the laccase-incorporated nanoflower has a high surface area, which may facilitate the mass transfer of the substrate and the product. FTIR spectrums identify the existence of laccase in the nanoflowers. The novel immobilized laccase was used for the synthesis of viniferin. The reaction conditions had been optimized and the laccase-incorporated nanoflower can show its maximum specific activity (16.3 µmol/g/h) under the optimal reaction conditions. The specific activity of the laccase in the nanoflowers is enhanced about 2.2-fold compared with free laccase in solution without copper (II) ions. Furthermore, the laccase in the nanoflowers shows an increase in specific activity of ~180% compared with free laccase in a solution containing high concentrations (similar to the concentration in the flower) of copper (II) ions. The results also indicate that the laccase in the nanoflowers retain 93.2% of its initial specific activity even after ten continuous batches. Full article
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Open AccessFeature PaperArticle
Immobilized Palladium Nanoparticles on Zirconium Carboxy-Aminophosphonates Nanosheets as an Efficient Recoverable Heterogeneous Catalyst for Suzuki–Miyaura and Heck Coupling
Catalysts 2017, 7(6), 186; doi:10.3390/catal7060186 -
Abstract
Zirconium phosphate glycine diphosphonate nanosheets (ZPGly) have been used as support for the preparation of solid palladium nanoparticles, namely Pd@ZPGly. Thanks to the presence of carboxy-aminophosponate groups on the layer surface, ZPGly-based materials were able to stabilize a high amount of palladium (up
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Zirconium phosphate glycine diphosphonate nanosheets (ZPGly) have been used as support for the preparation of solid palladium nanoparticles, namely Pd@ZPGly. Thanks to the presence of carboxy-aminophosponate groups on the layer surface, ZPGly-based materials were able to stabilize a high amount of palladium (up to 22 wt %) also minimizing the amount of metal leached in the final products of representative important cross-coupling processes selected for proving the catalysts’ efficiency. The catalytic systems have been fully characterized and used in low amounts (0.1 mol %) in the Suzuki–Miyaura and Heck cross-couplings. Moreover, the protocols were optimized for the use of recoverable azeotropic mixtures (aq. EtOH 96% or aq. CH3CN 84%, respectively) and in the flow procedure allowing one to isolate the final pure products, without any purification step, with very low residual palladium content and with a very low waste production. Full article
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Open AccessReview
Potential of Pervaporation and Vapor Separation with Water Selective Membranes for an Optimized Production of Biofuels—A Review
Catalysts 2017, 7(6), 187; doi:10.3390/catal7060187 -
Abstract
The development of processes based on the integration of new technologies is of growing interest to industrial catalysis. Recently, significant efforts have been focused on the design of catalytic membrane reactors to improve process performance. In particular, the use of membranes, that allow
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The development of processes based on the integration of new technologies is of growing interest to industrial catalysis. Recently, significant efforts have been focused on the design of catalytic membrane reactors to improve process performance. In particular, the use of membranes, that allow a selective permeation of water from the reaction mixture, positively affects the reaction evolution by improving conversion for all reactions thermodynamically or kinetically limited by the presence of water. In this paper, how pervaporation (PV) and vapor permeation (VP) technologies can improve the catalytic performance of reactions of industrial interest is considered. Specifically, technological approaches proposed in the literature are discussed with the aim of highlighting advantages and problems encountered in order to address research towards the optimization of membrane reactor configurations for liquid biofuel production in large scale. Full article
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Open AccessArticle
Preparation of ZnO-Loaded Lignin-Based Carbon Fiber for the Electrocatalytic Oxidation of Hydroquinone
Catalysts 2017, 7(6), 180; doi:10.3390/catal7060180 -
Abstract
To improve the hydroquinone (HQ) determination limit in wastewater and contribute to the comprehensive utilization of lignin, a zinc oxide-loaded lignin-based carbon fiber (ZCF) was prepared by a combination of electrospinning and thermal treatment processes, and was applied in electrocatalytic oxidation of HQ
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To improve the hydroquinone (HQ) determination limit in wastewater and contribute to the comprehensive utilization of lignin, a zinc oxide-loaded lignin-based carbon fiber (ZCF) was prepared by a combination of electrospinning and thermal treatment processes, and was applied in electrocatalytic oxidation of HQ using cyclic voltammetry (CV). The characterization of composites was conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The CV curves demonstrate that a ZCF-modified electrode can efficiently enhance the electrochemical signal and provide a fast response to HQ with a linear range from 1 × 10−6 to 5 × 10−3 mol/L and a determination limit of 2.5 × 10−7 M. Compared with modification materials reported in other literature, it performs excellent. In addition, the effect of the scan rate and the stability of modified materials were also investigated to illustrate the electrochemical behavior on HQ determination. Under optimum conditions, the ZCF-modified electrode was also used for the simultaneous determination of HQ, catechol (CC), and resorcinol (RS), which could well separate the oxidation peaks of the three isomers. Full article
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Open AccessArticle
Effect of Ce/Y Addition on Low-Temperature SCR Activity and SO2 and H2O Resistance of MnOx/ZrO2/MWCNTs Catalysts
Catalysts 2017, 7(6), 181; doi:10.3390/catal7060181 -
Abstract
The effects of SO2 and H2O on the low-temperature selective catalytic reduction (SCR) activity over MnOx/ZrO2/MWCNTs and MnOx/ZrO2/MWCNTs catalysts modified by Ce or Y was studied. MnCeZr and MnYZr catalysts reached nearly
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The effects of SO2 and H2O on the low-temperature selective catalytic reduction (SCR) activity over MnOx/ZrO2/MWCNTs and MnOx/ZrO2/MWCNTs catalysts modified by Ce or Y was studied. MnCeZr and MnYZr catalysts reached nearly 100% and 93.9% NOx conversions at 200 °C and 240 °C, respectively. They displayed a better SO2 tolerance, and the effect of H2O was negligible. The structural properties of the catalysts were characterized by XRD, H2-TPR, XPS, and FTIR before and after the reaction. The results showed that Ce could increase the mobility of the oxygen and improve the valence and the oxidizability of manganese, while the effect of Y was the opposite. This might be the main reason why the catalytic activity of MnCeZr was better than MnYZr in the presence or absence of SO2 and H2O. Doping Ce or Y broadened the active temperature window. Ce or Y, which existed in the catalysts with a high dispersion or at the amorphous state, preferred to react with SO2 to form sulfate species, and protected the manganese active sites from combing with SO2 to some extent, which coincided with the theory of ionic polarization. Full article
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Open AccessArticle
Insights into the Metal Salt Catalyzed 5-Ethoxymethylfurfural Synthesis from Carbohydrates
Catalysts 2017, 7(6), 182; doi:10.3390/catal7060182 -
Abstract
The use of common metal salts as catalysts for 5-ethoxymethylfurfural (EMF) synthesis from carbohydrate transformation was performed. Initial screening suggested AlCl3 as an efficient catalyst for EMF synthesis (45.0%) from fructose at 140 °C. Interestingly, CuSO4 and Fe2(SO4)3 were found to yield comparable
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The use of common metal salts as catalysts for 5-ethoxymethylfurfural (EMF) synthesis from carbohydrate transformation was performed. Initial screening suggested AlCl3 as an efficient catalyst for EMF synthesis (45.0%) from fructose at 140 °C. Interestingly, CuSO4 and Fe2(SO4)3 were found to yield comparable EMF at lower temperature of 110 to 120 °C, and high yields of ethyl levulinate (65.4–71.8%) were obtained at 150 °C. However, these sulfate salts were inactive in EMF synthesis from glucose and the major product was ethyl glucoside with around 80% yield, whereas EMF of 15.2% yield could be produced from glucose using CrCl3. The conversion of sucrose followed the accumulation of the reaction pathways of fructose and glucose, and a moderate yield of EMF could be achieved. Full article
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Open AccessReview
Review on Copper and Palladium Based Catalysts for Methanol Steam Reforming to Produce Hydrogen
Catalysts 2017, 7(6), 183; doi:10.3390/catal7060183 -
Abstract
Methanol steam reforming is a promising technology for producing hydrogen for onboard fuel cell applications. The methanol conversion rate and the contents of hydrogen, carbon monoxide and carbon dioxide in the reformate, significantly depend on the reforming catalyst. Copper-based catalysts and palladium-based catalysts
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Methanol steam reforming is a promising technology for producing hydrogen for onboard fuel cell applications. The methanol conversion rate and the contents of hydrogen, carbon monoxide and carbon dioxide in the reformate, significantly depend on the reforming catalyst. Copper-based catalysts and palladium-based catalysts can effectively convert methanol into hydrogen and carbon dioxide. Copper and palladium-based catalysts with different formulations and compositions have been thoroughly investigated in the literature. This work summarized the development of the two groups of catalysts for methanol steam reforming. Interactions between the activity components and the supports as well as the effects of different promoters were discussed. Compositional and morphological characteristics, along with the methanol steam reforming performances of different Cu/ZnO and Pd/ZnO catalysts promoted by Al2O3, CeO2, ZrO2 or other metal oxides, were reviewed and compared. Moreover, the reaction mechanism of methanol steam reforming over the copper based and palladium based catalysts were discussed. Full article
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Open AccessArticle
Catalytic Acetalization: An Efficient Strategy for High-Value Utilization of Biodiesel-Derived Glycerol
Catalysts 2017, 7(6), 184; doi:10.3390/catal7060184 -
Abstract
In this study, an efficient process for high value utilization of biodiesel-derived glycerolwas proposed via a simple reaction of acetalization catalyzed by novel catalysts of ester sulfate-functionalized ionic liquids (ILs). The relationship between the IL structure and its catalytic activity was investigated.
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In this study, an efficient process for high value utilization of biodiesel-derived glycerolwas proposed via a simple reaction of acetalization catalyzed by novel catalysts of ester sulfate-functionalized ionic liquids (ILs). The relationship between the IL structure and its catalytic activity was investigated. The effects of reaction conditions, and the substrate adaptability, were also carefully studied. The results demonstrate that ester sulfate-functionalized IL shows excellent catalytic activity on the acetalization of glycerol with aldehyde (ketone). Under the optimized condition, 87% glycerol conversion was obtained with 99% acetal selectivity when glycerol was condensed with cyclohexanone. In particular, 29% of product consists of six-membered compound, an important fine chemical and an excellent precursor in organic chemistry, because of the significant steric-hindrance effect of IL catalyst. Furthermore, the IL catalyst shows good recyclability where insignificant activity loss was exhibited even after six runs. Full article
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Open AccessCommunication
Lipase-Catalyzed Synthesis of Indolyl 4H-Chromenes via a Multicomponent Reaction in Ionic Liquid
Catalysts 2017, 7(6), 185; doi:10.3390/catal7060185 -
Abstract
Synthesis of indolyl 4H-chromenes via a three-component reaction catalyzed by lipase in ionic liquidsis reported here for the first time. High yields (77–98%) were obtained when Mucor miehei lipase was used as the catalyst in [EMIM][BF4]. Furthermore, [EMIM][BF4] exhibited
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Synthesis of indolyl 4H-chromenes via a three-component reaction catalyzed by lipase in ionic liquidsis reported here for the first time. High yields (77–98%) were obtained when Mucor miehei lipase was used as the catalyst in [EMIM][BF4]. Furthermore, [EMIM][BF4] exhibited good reusability in this enzymatic reaction. This study affords a new example of lipase catalytic promiscuity and broadens the application range of ionic liquid in biocatalysis. Full article
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Open AccessArticle
Conversion of Furans by Baeyer-Villiger Monooxygenases
Catalysts 2017, 7(6), 179; doi:10.3390/catal7060179 -
Abstract
Various furans are considered as valuable platform chemicals as they can be derived from plant biomass. Yet, for their exploitation, follow-up chemistry is required. Here we demonstrate that Baeyer-Villiger monooxygenases (BVMOs) can be used as biocatalysts for the selective oxidation of several furans,
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Various furans are considered as valuable platform chemicals as they can be derived from plant biomass. Yet, for their exploitation, follow-up chemistry is required. Here we demonstrate that Baeyer-Villiger monooxygenases (BVMOs) can be used as biocatalysts for the selective oxidation of several furans, including 5-(hydroxymethyl) furfural (HMF) and furfural. A total of 15 different BVMOs were tested for their activity on furfural, which revealed that most of the biocatalysts were active on this aromatic aldehyde. Phenylacetone monooxygenase (PAMO) and a mutant thereof (PAMOM446G) were selected for studying their biocatalytic potential in converting furfural and some other furans. While BVMOs are usually known to form an ester or lactone as a ‘normal’ product by inserting an oxygen atom adjacent to the carbonyl carbon of the substrate, our results reveal that both biocatalysts produce furanoid acids as the main product from the corresponding aldehydes. Altogether, our study shows that BVMOs can be employed for the selective oxidation of furans. Full article
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Open AccessArticle
Immobilization of Lipases on Magnetic Collagen Fibers and Its Applications for Short-Chain Ester Synthesis
Catalysts 2017, 7(6), 178; doi:10.3390/catal7060178 -
Abstract
Magnetic nanoparticles (MNp) Fe3O4 were prepared by chemical coprecipitation, and introduced onto collagen fibers to form magnetic collagen support (MNp-Col) for enzyme immobilization. Candida rugosa lipase has been successfully immobilized on MNp-Col supports by a covalent bond cross-linking agent, glutaraldehyde.
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Magnetic nanoparticles (MNp) Fe3O4 were prepared by chemical coprecipitation, and introduced onto collagen fibers to form magnetic collagen support (MNp-Col) for enzyme immobilization. Candida rugosa lipase has been successfully immobilized on MNp-Col supports by a covalent bond cross-linking agent, glutaraldehyde. The characteristics of MNp-Col and the immobilized lipase were investigated. The immobilized lipase displayed sound magnetic separation abilities in both aqueous and organic media. The activity of the immobilized lipase reached 2390 U/g under optimal conditions. The MNp-Col immobilized lipase shows broadened temperature and pH ranges for hydrolysis of olive oil emulsion. For synthesis of butyrate esters in an n-hexane medium, the yield changes through use of different alcohols, among which, butyric butyrate showed the highest yield. The prepared magnetic collagen fiber provides separation support for enzyme immobilization and has the potential to be used in other biotechnology fields. Full article
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Open AccessFeature PaperArticle
Zirconium Phosphate Heterostructures as Catalyst Support in Hydrodeoxygenation Reactions
Catalysts 2017, 7(6), 176; doi:10.3390/catal7060176 -
Abstract
A porous phosphate heterostructure (PPHs) formed by a layered zirconium(IV) phosphate expanded with silica galleries was prepared presenting a P/Zr molar ratio equal to 2 and a (Si + Zr)/P ratio equal to 3. This pillared zirconium phosphate heterostructure was used as a
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A porous phosphate heterostructure (PPHs) formed by a layered zirconium(IV) phosphate expanded with silica galleries was prepared presenting a P/Zr molar ratio equal to 2 and a (Si + Zr)/P ratio equal to 3. This pillared zirconium phosphate heterostructure was used as a catalyst support for bi-functional catalysts based on noble metals (Pt or Pd) and molybdenum oxide containing a total metallic loading of 2 wt % and Pt(Pd)/Mo molar ratio equal to 1. The catalysts prepared were characterized by different experimental techniques and evaluated in the hydrodeoxygenation (HDO) reaction of dibenzofuran (DBF) as a model compound present in biomass derived bio-oil, at different reaction pressures. The catalyst characterization evidenced that a high dispersion of the active phase can be achieved by using these materials, as observed from transmission electron microscopy (TEM) characterization, where the presence of small particles in the nanometric scale is noticeable. Moreover, the textural and acidic properties of the phosphate heterostructure are barely affected by the incorporation of metals into its structure. Characterization results evidenced that the presented material is a good candidate to be used as a material support. In both cases, high conversions and high selectivities to deoxygenated compounds were achieved and the active phase played an important role. Thus, Pt/Mo presented a better hydrogenolysis capability, being more selective to O-free products; whereas, Pd/Mo showed a greater hydrogenation ability being more affected by changes in pressure conditions. Full article
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Open AccessReview
Unconventional Approaches Involving Cyclodextrin-Based, Self-Assembly-Driven Processes for the Conversion of Organic Substrates in Aqueous Biphasic Catalysis
Catalysts 2017, 7(6), 173; doi:10.3390/catal7060173 -
Abstract
Aqueous biphasic catalysis is a convenient approach to convert organic, partially soluble molecules in water. However, converting more hydrophobic substrates is much more challenging as their solubility in water is extremely low. During the past ten years, substantial progress has been made towards
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Aqueous biphasic catalysis is a convenient approach to convert organic, partially soluble molecules in water. However, converting more hydrophobic substrates is much more challenging as their solubility in water is extremely low. During the past ten years, substantial progress has been made towards improving the contact between hydrophobic substrates and a hydrophilic transition-metal catalyst. The main cutting-edge approaches developed in the field by using cyclodextrins as a supramolecular tool will be discussed and compared in this short review. Full article
Open AccessArticle
Carbon-Modified Mesoporous Anatase/TiO2(B) Whisker for Enhanced Activity in Direct Synthesis of Hydrogen Peroxide by Palladium
Catalysts 2017, 7(6), 175; doi:10.3390/catal7060175 -
Abstract
The regulation of the interaction between H2O2 and its catalysts is a promising route to achieve high productivity and selectivity towards H2O2. Herein, mesoporous anatase/TiO2(B) whisker (mb-TiO2) modified with heterogeneous carbon was
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The regulation of the interaction between H2O2 and its catalysts is a promising route to achieve high productivity and selectivity towards H2O2. Herein, mesoporous anatase/TiO2(B) whisker (mb-TiO2) modified with heterogeneous carbon was prepared as the support of Pd-based catalysts for the direct synthesis of H2O2. The morphology and structure of the catalyst were investigated by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, Brunner-Emmet-Teller measurements, and X-ray photoelectron spectroscopy. The interaction between H2O2 and the support was studied by isothermal calorimeter. The carbon heterogeneous modification can weaken the interaction between H2O2 and the support, then accelerate the desorption of H2O2 and reduce the re-adsorption of H2O2 in the reaction medium. Meanwhile, the synergistic effects between TiO2 and Pd nanoparticles are not influenced by the heterogeneous carbon distribution. The catalyst exhibits better performance for the synthesis of H2O2 compared with the corresponding unmodified catalyst; the productivity of H2O2 increases more than 40%, which can be ascribed to the decrease of further H2O2 conversion under the weakened interaction. Full article
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Open AccessArticle
Nanostructured Ceria-Based Materials: Effect of the Hydrothermal Synthesis Conditions on the Structural Properties and Catalytic Activity
Catalysts 2017, 7(6), 174; doi:10.3390/catal7060174 -
Abstract
In this work, several nanostructured ceria catalysts were prepared by means of a hydrothermal procedure, in which the synthesis conditions (i.e., temperature and pH values) were varied. CeO2 samples of different shapes and structural properties were obtained, namely cubes, rods, cube and
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In this work, several nanostructured ceria catalysts were prepared by means of a hydrothermal procedure, in which the synthesis conditions (i.e., temperature and pH values) were varied. CeO2 samples of different shapes and structural properties were obtained, namely cubes, rods, cube and nanorod mixtures, and other polyhedra. The prepared materials were tested using four probe catalytic reactions: CO oxidation, NO oxidation, NOx-free soot oxidation, and NOx-assisted soot oxidation. The physicochemical properties of the prepared catalysts were studied by means of complementary techniques (i.e., XRD, N2-physisorption at −196 °C, CO-TPR (temperature-programmed reduction), field emission scanning electron microscopy (FESEM), micro-Raman spectroscopy). The abundance of defects of the catalysts, measured through in-situ Raman spectroscopy at the typical temperatures of each catalytic process, was correlated to the CO and NO oxidation activity of the prepared catalysts, while the soot oxidation reaction (performed in loose conditions), which was hindered by a poor soot-catalyst contact, was found to be less sensitive to the observed structural defects. Full article
Open AccessArticle
A Reusable Palladium/Cationic 2,2′-Bipyridyl System-Catalyzed Double Mizoroki-Heck Reaction in Water
Catalysts 2017, 7(6), 177; doi:10.3390/catal7060177 -
Abstract
A reusable PdCl2(NH3)2/cationic 2,2′-bipyridyl system was used to catalyze the double Mizoroki-Heck reaction of aryl iodides with electron-deficient alkenes in water in the absence of inert gas, giving β,β-diarylated carbonyl derivatives in good to excellent yields. The
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A reusable PdCl2(NH3)2/cationic 2,2′-bipyridyl system was used to catalyze the double Mizoroki-Heck reaction of aryl iodides with electron-deficient alkenes in water in the absence of inert gas, giving β,β-diarylated carbonyl derivatives in good to excellent yields. The formation of unsymmetrical β,β-diarylated alkenes were also studied by coupling aryl iodides with the corresponding aryl-substituted α,β-unsaturated carbonyl compounds. This water-soluble catalyst can be swiftly separated from the organic layer using simple extraction for the further reuse, and, thus, makes it an operationally-simple and environmentally-benign procedure. Full article
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