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Catalysts, Volume 7, Issue 9 (September 2017)

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Cover Story (view full-size image) Non-edible lignocellulosic biomass can be converted into drop-in biofuels via various routes among [...] Read more.
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Open AccessFeature PaperCommunication Halide-Enhanced Catalytic Activity of Palladium Nanoparticles Comes at the Expense of Catalyst Recovery
Catalysts 2017, 7(9), 280; https://doi.org/10.3390/catal7090280
Received: 24 July 2017 / Revised: 7 September 2017 / Accepted: 13 September 2017 / Published: 19 September 2017
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Abstract
In this communication, we present studies of the oxidative homocoupling of arylboronic acids catalyzed by immobilised palladium nanoparticles in aqueous solution. This reaction is of significant interest because it shares a key transmetallation step with the well-known Suzuki-Miyaura cross-coupling reaction. Additives can have
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In this communication, we present studies of the oxidative homocoupling of arylboronic acids catalyzed by immobilised palladium nanoparticles in aqueous solution. This reaction is of significant interest because it shares a key transmetallation step with the well-known Suzuki-Miyaura cross-coupling reaction. Additives can have significant effects on catalysis, both in terms of reaction mechanism and recovery of catalytic species, and our aim was to study the effect of added halides on catalytic efficiency and catalyst recovery. Using kinetic studies, we have shown that added halides (added as NaCl and NaBr) can increase the catalytic activity of the palladium nanoparticles more than 10-fold, allowing reactions to be completed in less than half a day at 30 °C. However, this increased activity comes at the expense of catalyst recovery. The results are in agreement with a reaction mechanism in which, under conditions involving high concentrations of chloride or bromide, palladium leaching plays an important role. Considering the evidence for analogous reactions occurring on the surface of palladium nanoparticles under different reaction conditions, we conclude that additives can exert a significant effect on the mechanism of reactions catalyzed by nanoparticles, including switching from a surface reaction to a solution reaction. The possibility of this switch in mechanism may also be the cause for the disagreement on this topic in the literature. Full article
(This article belongs to the Special Issue Catalysis in Innovative Solvents)
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Open AccessArticle Surface Oxidation of Supported Ni Particles and Its Impact on the Catalytic Performance during Dynamically Operated Methanation of CO2
Catalysts 2017, 7(9), 279; https://doi.org/10.3390/catal7090279
Received: 1 August 2017 / Revised: 25 August 2017 / Accepted: 5 September 2017 / Published: 18 September 2017
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Abstract
The methanation of CO2 within the power-to-gas concept was investigated under fluctuating reaction conditions to gather detailed insight into the structural dynamics of the catalyst. A 10 wt % Ni/Al2O3 catalyst with uniform 3.7 nm metal particles and a
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The methanation of CO2 within the power-to-gas concept was investigated under fluctuating reaction conditions to gather detailed insight into the structural dynamics of the catalyst. A 10 wt % Ni/Al2O3 catalyst with uniform 3.7 nm metal particles and a dispersion of 21% suitable to investigate structural changes also in a surface-sensitive way was prepared and characterized in detail. Operando quick-scanning X-ray absorption spectroscopy (XAS/QEXAFS) studies were performed to analyze the influence of 30 s and 300 s H2 interruptions during the methanation of CO2 in the presence of O2 impurities (technical CO2). These conditions represent the fluctuating supply of H2 from renewable energies for the decentralized methanation. Short-term H2 interruptions led to oxidation of the most reactive low-coordinated metallic Ni sites, which could not be re-reduced fully during the subsequent methanation cycle and accordingly caused deactivation. Detailed evaluation of the extended X-ray absorption fine structure (EXAFS) spectra showed surface oxidation/reduction processes, whereas the core of the Ni particles remained reduced. The 300-s H2 interruptions resulted in bulk oxidation already after the first cycle and a more pronounced deactivation. These results clearly show the importance and opportunities of investigating the structural dynamics of catalysts to identify their mechanism, especially in power-to-chemicals processes using renewable H2. Full article
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Open AccessArticle S- and N-Doped Graphene Nanomaterials for the Oxygen Reduction Reaction
Catalysts 2017, 7(9), 278; https://doi.org/10.3390/catal7090278
Received: 17 August 2017 / Revised: 15 September 2017 / Accepted: 16 September 2017 / Published: 18 September 2017
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Abstract
In the current work, heteroatom-doped graphene materials containing different atomic ratios of nitrogen and sulphur were employed as electrocatalysts for the oxygen reduction reaction (ORR) in acidic and alkaline media. To this end, the hydrothermal route and different chemical reducing agents were employed
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In the current work, heteroatom-doped graphene materials containing different atomic ratios of nitrogen and sulphur were employed as electrocatalysts for the oxygen reduction reaction (ORR) in acidic and alkaline media. To this end, the hydrothermal route and different chemical reducing agents were employed to synthesize the catalytic materials. The physicochemical characterization of the catalysts was performed by several techniques, such as X-ray diffraction, Raman spectroscopy and elemental analysis; meanwhile, the electrochemical performance of the materials toward the ORR was analyzed by linear sweep voltammetry (LSV), rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. The main results indicate that the ORR using heteroatom-doped graphene is a direct four-electron pathway, for which the catalytic activity is higher in alkaline than in acidic media. Indeed, a change of the reaction mechanism was observed with the insertion of N into the graphenic network, by the rate determining step changes from the first electrochemical step (formation of adsorbed OOH) on glassy carbon to the removal of adsorbed O (Oad) from the N-graphene surface. Moreover, the addition of sulphur atoms into the N-graphene structure increases the catalytic activity toward the ORR, as the desorption of Oad is accelerated. Full article
(This article belongs to the Special Issue Graphene-Based Materials for Energy Conversion)
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Open AccessArticle A New Homo-Hexamer Mn-Containing Catalase from Geobacillus sp. WCH70
Catalysts 2017, 7(9), 277; https://doi.org/10.3390/catal7090277
Received: 2 August 2017 / Revised: 29 August 2017 / Accepted: 12 September 2017 / Published: 18 September 2017
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Abstract
Catalase is an effective biocatalyst to degrade hydrogen peroxide to water and oxygen that can serve in textile effluent treatment to remove residual H2O2. Thermostable catalases are needed to withstand both the high temperature and pH of textile wastewater.
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Catalase is an effective biocatalyst to degrade hydrogen peroxide to water and oxygen that can serve in textile effluent treatment to remove residual H2O2. Thermostable catalases are needed to withstand both the high temperature and pH of textile wastewater. We have cloned the Mn-containing catalase gene ACS24898.1 from Geobacillus sp. WCH70, which originated from thermophilic organisms, and expressed it in Escherichia coli in activated form. The recombinant protein has been purified to homogeneity and identified to be a new homo-hexamer Mn-containing catalase. The native molecular mass of the catalase has been measured to be 138 kDa by size-exclusion chromatography. The new enzyme has optimum catalyzed activity at pH 9.0 and a temperature of 75 °C. It is thermostable up to 70 °C for 8 h incubation and maintains 80% and 50% activity, respectively, at 80 °C after 5 h and 90 °C after 1 h. At 75 °C and pH 9.0, the Km is 67.26 mM for substrate H2O2 and the rate of reaction at H2O2 saturation, Vmax, is 75,300 U/mg. The thermophilic and alkaline preferred properties of this new Mn-catalase are valuable features in textile wastewater treatment. Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
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Open AccessArticle The Preparation of a Highly Efficient Ag3PO4/Ag/Bi2O2CO3 Photo-Catalyst and the Study of Its Photo-Catalytic Organic Synthesis Reaction Driven by Visible Light
Catalysts 2017, 7(9), 276; https://doi.org/10.3390/catal7090276
Received: 18 August 2017 / Revised: 14 September 2017 / Accepted: 14 September 2017 / Published: 17 September 2017
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Abstract
Ag3PO4/Ag/Bi2O2CO3 composites were prepared by a hydrothermal and precipitation method. The morphology, structure, and valence state of the photo-catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Scanning
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Ag3PO4/Ag/Bi2O2CO3 composites were prepared by a hydrothermal and precipitation method. The morphology, structure, and valence state of the photo-catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface areas, and UV-vis diffuse reflectance spectra (UV-vis DRS). They were applied as heterogeneous catalysts in the synthesis of esters from aldehydes (or alcohols) and alcohols and the synthesis of imines from alcohols and amines under visible light irradiation. The photo-catalytic activities of the esterification reactions of aldehydes and alcohols were heavily dependent on the loading of Ag3PO4/Ag/Bi2O2CO3 as well as the intensity and wavelength of the visible light. Furthermore, their conversion under visible light irradiation was superior to that in the dark. Herein a reaction mechanism from aldehydes and alcohols to esters was proposed, and the Ag3PO4/Ag/Bi2O2CO3 catalysts could be used six times without a significant decrease in activity. Using these catalysts under visible light could motivate future studies to develop efficient recyclable photo-catalysts and facilitate many synthetic organic reactions. Full article
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Open AccessArticle Improving the Indigo Carmine Decolorization Ability of a Bacillus amyloliquefaciens Laccase by Site-Directed Mutagenesis
Catalysts 2017, 7(9), 275; https://doi.org/10.3390/catal7090275
Received: 14 August 2017 / Revised: 29 August 2017 / Accepted: 12 September 2017 / Published: 15 September 2017
Cited by 3 | PDF Full-text (2593 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Indigo carmine is a typical recalcitrant dye which is widely used in textile dyeing processes. Laccases are versatile oxidases showing strong ability to eliminate hazardous dyes from wastewater. However, most laccases require the participation of mediators for efficient decolorization of indigo carmine. Here
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Indigo carmine is a typical recalcitrant dye which is widely used in textile dyeing processes. Laccases are versatile oxidases showing strong ability to eliminate hazardous dyes from wastewater. However, most laccases require the participation of mediators for efficient decolorization of indigo carmine. Here we describe the improvement of the decolorization ability of a bacterial laccase through site-directed mutagenesis. A D501G variant of Bacillus amyloliquefaciens laccase was constructed and overexpressed in Escherichia coli. The laccase activity in the culture supernatant achieved 3374 U·L−1 for the mutant. Compared with the wild-type enzyme, the D501G exhibited better stability and catalytic efficiency. It could decolorize more than 92% of indigo carmine without additional mediators in 5 h at pH 9.0, which was 3.5 times higher than the wild-type laccase. Isatin sulfonic acid was confirmed to be the main product of indigo carmine degradation by UV-vis and LC-MS analyses. Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
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Open AccessArticle Electrocarboxylation of Dichlorobenzenes on a Silver Electrode in DMF
Catalysts 2017, 7(9), 274; https://doi.org/10.3390/catal7090274
Received: 25 August 2017 / Revised: 12 September 2017 / Accepted: 13 September 2017 / Published: 15 September 2017
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Abstract
Carbon dioxide (CO2) is the largest contributor to the greenhouse effect, and fixing and using this greenhouse gas in a facile manner is crucial. This work investigates the electrocarboxylation of dichlorobenzenes with the atmospheric pressure of CO2 in an undivided
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Carbon dioxide (CO2) is the largest contributor to the greenhouse effect, and fixing and using this greenhouse gas in a facile manner is crucial. This work investigates the electrocarboxylation of dichlorobenzenes with the atmospheric pressure of CO2 in an undivided cell with an Ag cathode and an Mg sacrificial anode. The corresponding carboxylic acids and their derivatives, which are important industrial and fine chemicals, are obtained. To deeply understand this reaction, we investigate the influence of various reaction conditions, such as supporting electrolyte, current density, electric charge, and reaction temperature, on the electrocarboxylation yield by using 1,4-dichlorobenzene as the model compound. The electrochemical behavior of dichlorobenzenes is studied through cyclic voltammetry. The relation among the distinct electronic effects of dichlorobenzenes, the electrochemical characteristics of their reduction, and the distribution law of target products is also established. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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Open AccessArticle The Isomerization of Limonene over the Ti-SBA-15 Catalyst—The Influence of Reaction Time, Temperature, and Catalyst Content
Catalysts 2017, 7(9), 273; https://doi.org/10.3390/catal7090273
Received: 10 August 2017 / Revised: 6 September 2017 / Accepted: 12 September 2017 / Published: 14 September 2017
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Abstract
The isomerization of limonene over the Ti-SBA-15 catalyst, which was prepared by the hydrothermal method, was studied. The main products of limonene isomerization were terpinolene, α-terpinene, γ-terpinene, and p-cymene—products with numerous applications. The amount of these products depended on reaction time, temperature, and
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The isomerization of limonene over the Ti-SBA-15 catalyst, which was prepared by the hydrothermal method, was studied. The main products of limonene isomerization were terpinolene, α-terpinene, γ-terpinene, and p-cymene—products with numerous applications. The amount of these products depended on reaction time, temperature, and catalyst content. These parameters changed in the following range: reaction time 30–1380 min, temperature 140–160 °C, and catalyst content 5–15 wt %. Finally, the most favorable conditions for the limonene isomerization process were established: a reaction time of 180 min, temperature of 160 °C, and amount of the catalyst 15 wt %. In order to obtain p-cymene (dehydroaromatization product), the most favorable conditions are similar but the reaction time should be 1380 min. The application of such conditions allowed us to obtain the highest amounts of the desired products in the shortest time. Full article
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Open AccessArticle The Catalytic Hydrogenation of Maleic Anhydride on CeO2−δ-Supported Transition Metal Catalysts
Catalysts 2017, 7(9), 272; https://doi.org/10.3390/catal7090272
Received: 11 August 2017 / Revised: 3 September 2017 / Accepted: 8 September 2017 / Published: 14 September 2017
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Abstract
The proper selection of transition metals and support is pivotal to the design of active and selective catalysts for maleic anhydride hydrogenation (MAH). Herein, the M/CeO2−δ (M = Co, Ni, Cu, respectively) catalysts with pre-optimised metal loading of 10 wt % were
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The proper selection of transition metals and support is pivotal to the design of active and selective catalysts for maleic anhydride hydrogenation (MAH). Herein, the M/CeO2−δ (M = Co, Ni, Cu, respectively) catalysts with pre-optimised metal loading of 10 wt % were prepared via a wet impregnation method and well characterized to corroborate their MAH performance with the properties of metal, support and the M/CeO2−δ catalysts. The results revealed that the metal dispersion on the catalyst declines in the order of Ni/CeO2−δ > Co/CeO2−δ > Cu/CeO2−δ, similar to the apparent activity for maleic anhydride (MA) transformation to succinic anhydride (SA). The hydrogenolysis of SA to γ-butyrolactone (GBL) occurs on Ni/CeO2−δ and Co/CeO2−δ only when the MA → SA transformation completing. The Ni/CeO2−δ displays superior activity and selectivity to Co/CeO2−δ in both MA → SA and SA → GBL reactions, while the Cu/CeO2−δ and CeO2−δ are both inert for SA → GBL hydrogenolysis. The MA hydrogenation to SA follows the first order kinetic law on the Ni/CeO2−δ and Co/CeO2−δ catalysts yet a more complex kinetic characteristics observed on the Cu/CeO2−δ. The distinct catalytic hydrogenation behaviours of the M/CeO2−δ catalysts are assigned to the synergism of dispersion and electronic configuration of the transition metals and oxygen vacancies. Full article
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Open AccessArticle Catalytic Characteristics of New Antibacterials Based on Hexahistidine-Containing Organophosphorus Hydrolase
Catalysts 2017, 7(9), 271; https://doi.org/10.3390/catal7090271
Received: 30 August 2017 / Revised: 8 September 2017 / Accepted: 11 September 2017 / Published: 14 September 2017
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Abstract
Catalytic characteristics of hexahistidine-containing organophosphorus hydrolase (His6-OPH) and its enzyme-polyelectrolyte complexes with poly-l-glutamic acid or poly-l-aspartic acid (His6-OPH/PLD50), hydrolyzing organophosphorous compounds, and N-acyl homoserine lactones were studied in the presence of various
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Catalytic characteristics of hexahistidine-containing organophosphorus hydrolase (His6-OPH) and its enzyme-polyelectrolyte complexes with poly-l-glutamic acid or poly-l-aspartic acid (His6-OPH/PLD50), hydrolyzing organophosphorous compounds, and N-acyl homoserine lactones were studied in the presence of various antibiotics (ampicillin, gentamicin, kanamycin, and rifampicin). The antibiotics at concentrations below 1 g·L−1 had a negligible inhibiting effect on the His6-OPH activity. Mixed inhibition of His6-OPH was established for higher antibiotic concentrations, and rifampicin was the most potent inhibitor. Stabilization of the His6-OPH activity was observed in the presence of antibiotics at a concentration of 0.2 g·L−1 during exposure at 25–41 °C. Molecular docking of antibiotics to the surface of His6-OPH dimer revealed the antibiotics binding both to the area near active centers of the enzyme subunits and to the region of contact between subunits of the dimer. Such interactions between antibiotics and His6-OPH were verified with Fourier-transform infrared (FTIR) spectroscopy. Considering all the results of the study, the combination of His6-OPH/PLD50 with β-lactam antibiotic ampicillin was established as the optimal one in terms of exhibition and persistence of maximal lactonase activity of the enzyme. Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
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Open AccessArticle Promotion of Ca-Co Bifunctional Catalyst/Sorbent with Yttrium for Hydrogen Production in Modified Chemical Looping Steam Methane Reforming Process
Catalysts 2017, 7(9), 270; https://doi.org/10.3390/catal7090270
Received: 6 June 2017 / Revised: 4 August 2017 / Accepted: 17 August 2017 / Published: 13 September 2017
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Abstract
In this study, the application of a calcium-based bifunctional catalyst/sorbent is investigated in modified chemical looping steam methane reforming (CLSMR) process for in situ CO2 sorption and H2 production. The yttrium promoted Ca-Co samples were synthesized and applied as bifunctional catalysts/sorbent.
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In this study, the application of a calcium-based bifunctional catalyst/sorbent is investigated in modified chemical looping steam methane reforming (CLSMR) process for in situ CO2 sorption and H2 production. The yttrium promoted Ca-Co samples were synthesized and applied as bifunctional catalysts/sorbent. The influence of reduction temperature (500–750 °C), Ca/Co and Ca/Y ratios (1.5–∞ and 3–18, respectively) and catalyst life time are determined in CLSMR process. The physicochemical transformation of fresh, used and regenerated samples after 16 redox cycles are determined using X-ray powder diffraction (XRD), N2 adsorption–desorption, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM) techniques. The effect of yttrium promoter on the structure of catalyst and regeneration step on the reversibility of bifunctional catalyst/sorbent was two important factors. The characterization results revealed that the presence of yttrium in the structure of Ca-9Co sample could improve the morphology and textural properties of catalyst/sorbents. The suitable reversibility of bifunctional catalyst/sorbents during the repeated cycles is confirmed by characterization of calcined samples. The Ca-9Co-4.5Y as optimal catalyst illustrated superior performance and stability. It showed about 95.8% methane conversion and 82.9% hydrogen yield at 700 °C and stable activity during 16 redox cycles. Full article
(This article belongs to the Special Issue Reforming Catalysts)
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Open AccessArticle Selective Acetylation of Small Biomolecules and Their Derivatives Catalyzed by Er(OTf)3
Catalysts 2017, 7(9), 269; https://doi.org/10.3390/catal7090269
Received: 21 July 2017 / Revised: 5 September 2017 / Accepted: 6 September 2017 / Published: 12 September 2017
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Abstract
It is of great significance to develop sustainable processes of catalytic reaction. We report a selective procedure for the synthesis of acetylated bioactive compounds in water. The use of 1-acetylimidazole combined with Er(OTf)3 as a Lewis acid catalyst gives high regioselectivity and
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It is of great significance to develop sustainable processes of catalytic reaction. We report a selective procedure for the synthesis of acetylated bioactive compounds in water. The use of 1-acetylimidazole combined with Er(OTf)3 as a Lewis acid catalyst gives high regioselectivity and good yields for the acetylation of primary hydroxyl groups, as well as amino groups. The protection is achieved in short reaction times under microwave irradiation, and is successful even in the case of base-sensitive substrates. Full article
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Open AccessArticle Pulse Microcalorimetry Study of Methane Dry Reforming Reaction on Ni/Ceria-Zirconia Catalyst
Catalysts 2017, 7(9), 268; https://doi.org/10.3390/catal7090268
Received: 24 August 2017 / Revised: 6 September 2017 / Accepted: 7 September 2017 / Published: 12 September 2017
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Abstract
For Ni/CeZrO catalyst prepared in supercritical isopropanol main features of methane dry reforming reaction mechanism were studied by the pulse microcalorimetric technique. The reaction scheme is described by a step-wise redox mechanism with independent stages of CH4 transformation on Ni/support interface producing
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For Ni/CeZrO catalyst prepared in supercritical isopropanol main features of methane dry reforming reaction mechanism were studied by the pulse microcalorimetric technique. The reaction scheme is described by a step-wise redox mechanism with independent stages of CH4 transformation on Ni/support interface producing syngas with participation of support oxygen bridging species (the rate-limiting stage) and fast reoxidation of support sites by CO2 yielding CO regenerating reactive oxygen species. Full article
(This article belongs to the Special Issue Conversion of CO2 into CO Using Heterogeneous Catalysis)
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Open AccessReview Heck Reaction—State of the Art
Catalysts 2017, 7(9), 267; https://doi.org/10.3390/catal7090267
Received: 20 August 2017 / Revised: 5 September 2017 / Accepted: 6 September 2017 / Published: 11 September 2017
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Abstract
The Heck reaction is one of the most studied coupling reactions and is recognized with the Nobel Prize in Chemistry. Thousands of articles, hundreds of reviews and a number of books have been published on this topic. All reviews are written exhaustively describing
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The Heck reaction is one of the most studied coupling reactions and is recognized with the Nobel Prize in Chemistry. Thousands of articles, hundreds of reviews and a number of books have been published on this topic. All reviews are written exhaustively describing the various aspects of Heck reaction and refer to the work done hitherto. Looking at the quantum of the monographs published, and the reviews based on them, we found a necessity to summarize all reviews on Heck reaction about catalysts, ligands, suggested mechanisms, conditions, methodologies and the compounds formed via Heck reaction in one review and generate a resource of information. One can find almost all the catalysts used so far for Heck reaction in this review. Full article
(This article belongs to the Special Issue Catalyzed Mizoroki–Heck Reaction or C–H activation)
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Open AccessArticle Flower-Like Au–CuO/Bi2WO6 Microsphere Catalysts: Synthesis, Characterization, and Their Catalytic Performances for CO Oxidation
Catalysts 2017, 7(9), 266; https://doi.org/10.3390/catal7090266
Received: 15 August 2017 / Revised: 30 August 2017 / Accepted: 5 September 2017 / Published: 11 September 2017
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Abstract
The flower-like Bi2WO6 microsphere was synthesized through a simple hydrothermal route, and three catalysts, Au/Bi2WO6, CuO/Bi2WO6, and Au–CuO/Bi2WO6, were prepared by a deposition–precipitation method. The morphology and structure
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The flower-like Bi2WO6 microsphere was synthesized through a simple hydrothermal route, and three catalysts, Au/Bi2WO6, CuO/Bi2WO6, and Au–CuO/Bi2WO6, were prepared by a deposition–precipitation method. The morphology and structure of the catalysts were characterized by X-ray powder diffraction, surface area analyzer, inductively coupled plasma optical emission spectrometer, scanning electron microscope, transmission electron microscopy, UV/Vis spectrometer, as well as X-ray photoelectron spectroscopy. Their catalytic performances in catalytic CO oxidation were evaluated. For Au/Bi2WO6 and CuO/Bi2WO6, Au and CuO nanoparticles highly dispersed on Bi2WO6 are 3 and 10 nm, respectively, in average size. For Au–CuO/Bi2WO6, a part of the Au nanoparticles (Au NPs) strongly adheres to the CuO, due to the strong interaction between Au NPs and CuO, which has a positive effect on catalytic activity of Au–CuO/Bi2WO6. Au–CuO/Bi2WO6 can convert CO into CO2 completely at 40 °C, as the contents of Au and Cu are 0.438 wt % and 4.85 wt %, respectively. Full article
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