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Catalysts, Volume 8, Issue 8 (August 2018)

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Cover Story (view full-size image) First time the application of D-glucose-modified photocatalyst on a cement mortar for water [...] Read more.
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Open AccessArticle Low-Temperature Electrocatalytic Conversion of CO2 to Liquid Fuels: Effect of the Cu Particle Size
Catalysts 2018, 8(8), 340; https://doi.org/10.3390/catal8080340
Received: 30 July 2018 / Revised: 9 August 2018 / Accepted: 14 August 2018 / Published: 20 August 2018
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Abstract
A novel gas-phase electrocatalytic system based on a low-temperature proton exchange membrane (Sterion) was developed for the gas-phase electrocatalytic conversion of CO2 to liquid fuels. This system achieved gas-phase electrocatalytic reduction of CO2 at low temperatures (below 90 °C) over a
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A novel gas-phase electrocatalytic system based on a low-temperature proton exchange membrane (Sterion) was developed for the gas-phase electrocatalytic conversion of CO2 to liquid fuels. This system achieved gas-phase electrocatalytic reduction of CO2 at low temperatures (below 90 °C) over a Cu cathode by using water electrolysis-derived protons generated in-situ on an IrO2 anode. Three Cu-based cathodes with varying metal particle sizes were prepared by supporting this metal on an activated carbon at three loadings (50, 20, and 10 wt %; 50% Cu-AC, 20% Cu-AC, and 10% Cu-AC, respectively). The cathodes were characterized by N2 adsorption–desorption, temperature-programmed reduction (TPR), and X-ray diffraction (XRD) and their performance towards the electrocatalytic conversion of CO2 was subsequently studied. The membrane electrode assembly (MEA) containing the cathode with the largest Cu particle size (50% Cu-AC, 40 nm) showed the highest CO2 electrocatalytic activity per mole of Cu, with methyl formate being the main product. This higher electrocatalytic activity was attributed to the lower Cu–CO bonding strength over large Cu particles. Different product distributions were obtained over 20% Cu-AC and 10% Cu-AC, with acetaldehyde and methanol being the main reaction products, respectively. The CO2 consumption rate increased with the applied current and reaction temperature. Full article
(This article belongs to the Special Issue Emissions Control Catalysis)
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Open AccessArticle Total Oxidation of Dichloromethane over Silica Modified Alumina Catalysts Washcoated on Ceramic Monoliths
Catalysts 2018, 8(8), 339; https://doi.org/10.3390/catal8080339
Received: 8 July 2018 / Revised: 8 August 2018 / Accepted: 17 August 2018 / Published: 20 August 2018
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Abstract
Silica modified alumina was used in this study for coating of a cordierite monolith substrate with two different channel densities. The performance of the prepared monolith catalysts was evaluated in catalytic total oxidation of dichloromethane before and after Pt impregnation. The characteristics similar
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Silica modified alumina was used in this study for coating of a cordierite monolith substrate with two different channel densities. The performance of the prepared monolith catalysts was evaluated in catalytic total oxidation of dichloromethane before and after Pt impregnation. The characteristics similar to the powder form catalysts were kept rather successfully after washcoating the monolith as evidenced by electron microscopy (FESEM) and N2 physisorption. A dichloromethane (DCM) conversion of higher than 80% at 500 °C was reached over all the catalysts with 200 cpsi. The maximum conversion was obtained with the catalyst containing 10 mol % of silica. The total amount of major byproducts (CO, CH3Cl and CH2O) were slightly decreased by increasing the silica loading, and remarkably after Pt impregnation. After impregnation of Pt, the HCl yields were increased for two samples with the higher loading of silica (10 and 15 mol %) and reached the maximum when silica loading was 10%. Even though Pt impregnation did not significantly affect the DCM conversion, it improved the selectivity. Comparison between the two substrates (200 and 600 cpsi) evidenced that the key parameters of the monolith influencing the DCM oxidation are low value of open fraction area, hydraulic diameter, thermal integrity factor and high value of mechanical integrity factor and geometric surface area. Full article
(This article belongs to the Special Issue Catalysts for Oxidative Destruction of Volatile Organic Compounds)
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Open AccessArticle Developing a High-Temperature Solvent-Free System for Efficient Biocatalysis of Octyl Ferulate
Catalysts 2018, 8(8), 338; https://doi.org/10.3390/catal8080338
Received: 27 July 2018 / Revised: 14 August 2018 / Accepted: 16 August 2018 / Published: 20 August 2018
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Abstract
Ferulic acid esters have been suggested as a group of natural chemicals that have the function of sunscreen. The study aimed to utilize an environmentally-friendly enzymatic method through the esterification of ferulic acid with octanol, producing octyl ferulate. The Box-Behnken experimental design for
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Ferulic acid esters have been suggested as a group of natural chemicals that have the function of sunscreen. The study aimed to utilize an environmentally-friendly enzymatic method through the esterification of ferulic acid with octanol, producing octyl ferulate. The Box-Behnken experimental design for response surface methodology (RSM) was performed to determine the synthesis effects of variables, including enzyme amount (1000–2000 propyl laurate units (PLU)), reaction temperature (70–90 °C), and stir speed (50–150 rpm) on the molar conversion of octyl ferulate. According to the joint test, both the enzyme amount and reaction temperature had great impacts on the molar conversion. An RSM-developed second-order polynomial equation further showed a data-fitting ability. Using ridge max analysis, the optimal parameters of the biocatalyzed reaction were: 72 h reaction time, 92.2 °C reaction temperature, 1831 PLU enzyme amount, and 92.4 rpm stir speed, respectively. Finally, the molar conversion of octyl ferulate under optimum conditions was verified to be 93.2 ± 1.5%. In conclusion, it has been suggested that a high yield of octyl ferulate should be synthesized under elevated temperature conditions with a commercial immobilized lipase. Our findings could broaden the utilization of the lipase and provide a biocatalytic approach, instead of the chemical method, for ferulic acid ester synthesis. Full article
(This article belongs to the Special Issue Biocatalysis: Chemical Biosynthesis)
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Open AccessArticle Effects of Coordination Ability of Nitrogen-Containing Carboxylic Acid Ligands on Nieuwland Catalyst
Catalysts 2018, 8(8), 337; https://doi.org/10.3390/catal8080337
Received: 21 July 2018 / Revised: 11 August 2018 / Accepted: 13 August 2018 / Published: 17 August 2018
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Abstract
This article investigated the effect of three nitrogen-containing carboxylic acid ligands for the Nieuwland catalyst system. The catalyst system containing 4.5% N-(2-acetamido) iminodiacetic acid exhibited improved catalytic activity with excellent performance. The yield of monovinylacetylene (MVA) was maintained at 36.7% after 24
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This article investigated the effect of three nitrogen-containing carboxylic acid ligands for the Nieuwland catalyst system. The catalyst system containing 4.5% N-(2-acetamido) iminodiacetic acid exhibited improved catalytic activity with excellent performance. The yield of monovinylacetylene (MVA) was maintained at 36.7% after 24 h, which was increased by 17.1% relative to the Nieuwland catalyst system. Based on a variety of analyses on the crystals precipitated from the catalyst solutions, it can be inferred that the outstanding performance and lifetime of the catalysts were related to the abilities of these ligands to form strong coordination with Cu+ ions and stabilize them. Full article
(This article belongs to the Section Metal Catalysis)
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Open AccessArticle Active Site of O2 and Its Improvement Mechanism over Ce-Ti Catalyst for NH3-SCR Reaction
Catalysts 2018, 8(8), 336; https://doi.org/10.3390/catal8080336
Received: 8 July 2018 / Revised: 3 August 2018 / Accepted: 6 August 2018 / Published: 17 August 2018
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Abstract
The current study on Ce-Ti catalyst was mainly focused on the function of NH3 and NO adsorption sites. In our study, by comparing Ce-Ti (doped catalyst) to Ce/Ti (supported catalyst), the active site of O2 and its improvement mechanism over Ce-Ti
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The current study on Ce-Ti catalyst was mainly focused on the function of NH3 and NO adsorption sites. In our study, by comparing Ce-Ti (doped catalyst) to Ce/Ti (supported catalyst), the active site of O2 and its improvement mechanism over Ce-Ti catalyst for NH3-Selective catalytic reduction (SCR) reactions were investigated. For Ce-Ti catalyst, a cerium atom was confirmed entering a TiO2 crystal lattice by X-ray diffraction (XRD) and Raman; the structure of Ce-□-Ti (□ represents oxygen vacancy) in Ce-Ti catalyst was confirmed by X-ray photoelectron spectroscopy (XPS) and Photoluminescence spectra (PL spectra). The nature of this structure was characterized by electron paramagnetic resonance (EPR), Ammonia temperature-programmed desorption (NH3-TPD), hydrogen temperature-programmed reduction (H2-TPR), Nitric oxide temperature-programmed desorption (NO-TPD) and In situ DRIFT. The results indicated that oxygen vacancies had a promotive effect on the adsorption and activation of oxygen, and oxygen was converted to superoxide ions in large quantities. Also, because of adsorption and activation of NO and NH3, electrons were transferred to adsorbed oxygen via oxygen vacancies, which also promoted the formation of superoxide ions. We expected that our study could promote understanding of the active site of O2 and its improvement mechanism for doped catalyst. Full article
(This article belongs to the Special Issue Active Sites in Catalytic Reaction)
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Open AccessArticle From a Sequential Chemo-Enzymatic Approach to a Continuous Process for HMF Production from Glucose
Catalysts 2018, 8(8), 335; https://doi.org/10.3390/catal8080335
Received: 13 July 2018 / Revised: 23 July 2018 / Accepted: 27 July 2018 / Published: 17 August 2018
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Abstract
Notably available from the cellulose contained in lignocellulosic biomass, glucose is a highly attractive substrate for eco-efficient processes towards high-value chemicals. A recent strategy for biomass valorization consists on combining biocatalysis and chemocatalysis to realise the so-called chemo-enzymatic or hybrid catalysis. Optimisation of
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Notably available from the cellulose contained in lignocellulosic biomass, glucose is a highly attractive substrate for eco-efficient processes towards high-value chemicals. A recent strategy for biomass valorization consists on combining biocatalysis and chemocatalysis to realise the so-called chemo-enzymatic or hybrid catalysis. Optimisation of the glucose conversion to 5-hydroxymethylfurfural (HMF) is the object of many research efforts. HMF can be produced by chemo-catalyzed fructose dehydration, while fructose can be selectively obtained from enzymatic glucose isomerization. Despite recent advances in HMF production, a fully integrated efficient process remains to be demonstrated. Our innovative approach consists on a continuous process involving enzymatic glucose isomerization, selective arylboronic-acid mediated fructose complexation/transportation, and chemical fructose dehydration to HMF. We designed a novel reactor based on two aqueous phases dynamically connected via an organic liquid membrane, which enabled substantial enhancement of glucose conversion (70%) while avoiding intermediate separation steps. Furthermore, in the as-combined steps, the use of an immobilized glucose isomerase and an acidic resin facilitates catalyst recycling. Full article
(This article belongs to the Special Issue Catalytic Methods in Flow Chemistry)
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Open AccessArticle Magnetic Combined Cross-Linked Enzyme Aggregates of Ketoreductase and Alcohol Dehydrogenase: An Efficient and Stable Biocatalyst for Asymmetric Synthesis of (R)-3-Quinuclidinol with Regeneration of Coenzymes In Situ
Catalysts 2018, 8(8), 334; https://doi.org/10.3390/catal8080334
Received: 14 July 2018 / Revised: 29 July 2018 / Accepted: 30 July 2018 / Published: 15 August 2018
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Abstract
Enzymes are biocatalysts. In this study, a novel biocatalyst consisting of magnetic combined cross-linked enzyme aggregates (combi-CLEAs) of 3-quinuclidinone reductase (QNR) and glucose dehydrogenase (GDH) for enantioselective synthesis of (R)-3-quinuclidinolwith regeneration of cofactors in situ was developed. The magnetic combi-CLEAs were
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Enzymes are biocatalysts. In this study, a novel biocatalyst consisting of magnetic combined cross-linked enzyme aggregates (combi-CLEAs) of 3-quinuclidinone reductase (QNR) and glucose dehydrogenase (GDH) for enantioselective synthesis of (R)-3-quinuclidinolwith regeneration of cofactors in situ was developed. The magnetic combi-CLEAs were fabricated with the use of ammonium sulfate as a precipitant and glutaraldehyde as a cross-linker for direct immobilization of QNR and GDH from E. coli BL(21) cell lysates onto amino-functionalized Fe3O4 nanoparticles. The physicochemical properties of the magnetic combi-CLEAs were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and magnetic measurements. Field emission scanning electron microscope (FE-SEM) images revealed a spherical structure with numerous pores which facilitate the movement of the substrates and coenzymes. Moreover, the magnetic combi-CLEAs exhibited improved operational and thermal stability, enhanced catalytic performance for transformation of 3-quinuclidinone (33 g/L) into (R)-3-quinuclidinol in 100% conversion yield and 100% enantiomeric excess (ee) after 3 h of reaction. The activity of the biocatalysts was preserved about 80% after 70 days storage and retained more than 40% of its initial activity after ten cycles. These results demonstrated that the magnetic combi-CLEAs, as cost-effective and environmentally friendly biocatalysts, were suitable for application in synthesis of (R)-3-quinuclidinol essential for the production of solifenacin and aclidinium with better performance than those currently available. Full article
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Open AccessArticle Stabilization of Enzymes by Multipoint Covalent Attachment on Aldehyde-Supports: 2-Picoline Borane as an Alternative Reducing Agent
Catalysts 2018, 8(8), 333; https://doi.org/10.3390/catal8080333
Received: 26 July 2018 / Revised: 8 August 2018 / Accepted: 11 August 2018 / Published: 15 August 2018
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Abstract
Enzyme immobilization by multipoint covalent attachment on supports activated with aliphatic aldehyde groups (e.g., glyoxyl agarose) has proven to be an excellent immobilization technique for enzyme stabilization. Borohydride reduction of immobilized enzymes is necessary to convert enzyme–support linkages into stable secondary amino groups
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Enzyme immobilization by multipoint covalent attachment on supports activated with aliphatic aldehyde groups (e.g., glyoxyl agarose) has proven to be an excellent immobilization technique for enzyme stabilization. Borohydride reduction of immobilized enzymes is necessary to convert enzyme–support linkages into stable secondary amino groups and to convert the remaining aldehyde groups on the support into hydroxy groups. However, the use of borohydride can adversely affect the structure–activity of some immobilized enzymes. For this reason, 2-picoline borane is proposed here as an alternative milder reducing agent, especially, for those enzymes sensitive to borohydride reduction. The immobilization-stabilization parameters of five enzymes from different sources and nature (from monomeric to multimeric enzymes) were compared with those obtained by conventional methodology. The most interesting results were obtained for bacterial (R)-mandelate dehydrogenase (ManDH). Immobilized ManDH reduced with borohydride almost completely lost its catalytic activity (1.5% of expressed activity). In contrast, using 2-picoline borane and blocking the remaining aldehyde groups on the support with glycine allowed for a conjugate with a significant activity of 19.5%. This improved biocatalyst was 357-fold more stable than the soluble enzyme at 50 °C and pH 7. The results show that this alternative methodology can lead to more stable and active biocatalysts. Full article
(This article belongs to the Special Issue Immobilization of Enzymes)
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Open AccessReview Mixed-Oxide Catalysts with Spinel Structure for the Valorization of Biomass: The Chemical-Loop Reforming of Bioethanol
Catalysts 2018, 8(8), 332; https://doi.org/10.3390/catal8080332
Received: 29 July 2018 / Revised: 10 August 2018 / Accepted: 12 August 2018 / Published: 14 August 2018
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Abstract
This short review reports on spinel-type mixed oxides as catalysts for the transformation of biomass-derived building blocks into chemicals and fuel additives. After an overview of the various methods reported in the literature for the synthesis of mixed oxides with spinel structure, the
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This short review reports on spinel-type mixed oxides as catalysts for the transformation of biomass-derived building blocks into chemicals and fuel additives. After an overview of the various methods reported in the literature for the synthesis of mixed oxides with spinel structure, the use of this class of materials for the chemical-loop reforming of bioalcohols is reviewed in detail. This reaction is aimed at the production of H2 with intrinsic separation of C-containing products, but also is a very versatile tool for investigating the solid-state chemistry of spinels. Full article
(This article belongs to the Special Issue Catalytic Processes for The Valorisation of Biomass Derived Molecules)
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Open AccessArticle Ru-(Mn-M)OX Solid Base Catalysts for the Upgrading of Xylitol to Glycols in Water
Catalysts 2018, 8(8), 331; https://doi.org/10.3390/catal8080331
Received: 26 July 2018 / Revised: 10 August 2018 / Accepted: 11 August 2018 / Published: 14 August 2018
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Abstract
A series of Ru-(Mn-M)OX catalysts (M: Al, Ti, Zr, Zn) prepared by co-precipitation were investigated in the hydrogenolysis of xylitol in water to ethylene glycol, propylene glycol and glycerol at 200 °C and 60 bar of H2. The catalyst promoted
[...] Read more.
A series of Ru-(Mn-M)OX catalysts (M: Al, Ti, Zr, Zn) prepared by co-precipitation were investigated in the hydrogenolysis of xylitol in water to ethylene glycol, propylene glycol and glycerol at 200 °C and 60 bar of H2. The catalyst promoted with Al, Ru-(Mn-Al)OX, showed superior activity (57 h−1) and a high global selectivity to glycols and glycerol of 58% at 80% xylitol conversion. In comparison, the catalyst prepared by loading Ru on (Mn-Al)OX, Ru/(Mn-Al)OX was more active (111 h−1) but less selective (37%) than Ru-(Mn-Al)OX. Characterization of these catalysts by XRD, BET, CO2-TPD, NH3-TPD and TEM showed that Ru/(Mn-Al)OX contained highly dispersed and uniformly distributed Ru particles and fewer basic sites, which favored decarbonylation, epimerization and cascade decarbonylation reactions instead of retro-aldol reactions producing glycols. The hydrothermal stability of Ru-(Mn-Al)OX was improved by decreasing the xylitol/catalyst ratio, which decreased the formation of carboxylic acids and enabled recycling of the catalyst, with a very low deactivation. Full article
(This article belongs to the Special Issue Solid Catalysts for the Upgrading of Renewable Sources)
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Open AccessArticle Constructing A Rational Kinetic Model of the Selective Propane Oxidation Over A Mixed Metal Oxide Catalyst
Catalysts 2018, 8(8), 330; https://doi.org/10.3390/catal8080330
Received: 14 July 2018 / Revised: 6 August 2018 / Accepted: 9 August 2018 / Published: 13 August 2018
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Abstract
This research presents a kinetic investigation of the selective oxidation of propane to acrylic acid over a MoVTeNb oxide (M1 phase) catalyst. The paper contains both an overview of the related literature, and original results with a focus on kinetic aspects. Two types
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This research presents a kinetic investigation of the selective oxidation of propane to acrylic acid over a MoVTeNb oxide (M1 phase) catalyst. The paper contains both an overview of the related literature, and original results with a focus on kinetic aspects. Two types of kinetic experiments were performed in a plug flow reactor, observing (i) steady-state conditions (partial pressure variations) and (ii) the catalyst evolution as a function of time-on-stream. For this, the catalyst was treated in reducing atmosphere, before re-oxidising it. These observations in long term behaviour were used to distinguish different catalytic routes, namely for the formation of propene, acetic acid, acrylic acid, carbon monoxide and carbon dioxide. A partial carbon balance was introduced, which is a ‘kinetic fingerprint’, that distinguishes one type of active site from another. Furthermore, an ‘active site’ was found to consist of one or more ‘active centres’. A rational mechanism was developed based on the theory of graphs and includes two time scales belonging to (i) the catalytic cycle and (ii) the catalyst evolution. Several different types of active sites exist, at least as many, as kinetically independent product molecules are formed over a catalyst surface. Full article
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Open AccessArticle Oxygen Reduction Reaction and Hydrogen Evolution Reaction Catalyzed by Pd–Ru Nanoparticles Encapsulated in Porous Carbon Nanosheets
Catalysts 2018, 8(8), 329; https://doi.org/10.3390/catal8080329
Received: 7 July 2018 / Revised: 25 July 2018 / Accepted: 2 August 2018 / Published: 11 August 2018
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Abstract
Developing bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for enhancing the energy transfer efficiency of metal–air batteries and fuel cells, as well as producing hydrogen with a high purity. Herein, a series of Pd–Ru alloyed
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Developing bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for enhancing the energy transfer efficiency of metal–air batteries and fuel cells, as well as producing hydrogen with a high purity. Herein, a series of Pd–Ru alloyed nanoparticles encapsulated in porous carbon nanosheets (CNs) were synthesized and employed as a bifunctional electrocatalyst for both ORR and HER. The TEM measurements showed that Pd–Ru nanoparticles, with a size of approximately 1–5 nm, were uniformly dispersed on the carbon nanosheets. The crystal and electronic structures of the PdxRu100−x/CNs series were revealed by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The as-prepared samples exhibited effective ORR activity in alkaline media and excellent HER activity in both alkaline and acid solutions. The Pd50Ru50/CNs sample displayed the best activity and stability among the series, which is comparable and superior to that of commercial 10% Pd/C. For ORR, the Pd50Ru50/CNs catalyst exhibited an onset potential of 0.903 V vs. RHE (Reversible Hydrogen Electrode) and 11.4% decrease of the current density after 30,000 s of continuous operation in stability test. For HER, the Pd50Ru50/CNs catalyst displayed an overpotential of 37.3 mV and 45.1 mV at 10 mA cm−2 in 0.1 M KOH and 0.5 M H2SO4, respectively. The strategy for encapsulating bimetallic alloys within porous carbon materials is promising for fabricating sustainable energy toward electrocatalysts with multiple electrocatalytic activities for energy related applications. Full article
(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)
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Open AccessArticle NiFeOx as a Bifunctional Electrocatalyst for Oxygen Reduction (OR) and Evolution (OE) Reaction in Alkaline Media
Catalysts 2018, 8(8), 328; https://doi.org/10.3390/catal8080328
Received: 29 June 2018 / Revised: 31 July 2018 / Accepted: 8 August 2018 / Published: 10 August 2018
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Abstract
This article reports the two-step synthesis of NiFeOx nanomaterials and their characterization and bifunctional electrocatalytic activity measurements in alkaline electrolyte for metal-air batteries. The samples were mostly in layered double hydroxide at the initial temperature, but upon heat treatment, they were converted
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This article reports the two-step synthesis of NiFeOx nanomaterials and their characterization and bifunctional electrocatalytic activity measurements in alkaline electrolyte for metal-air batteries. The samples were mostly in layered double hydroxide at the initial temperature, but upon heat treatment, they were converted to NiFe2O4 phases. The electrochemical behaviour of the different samples was studied by linear sweep voltammetry and cyclic voltammetry on the glassy carbon electrode. The OER catalyst activity was observed for low mass loadings (0.125 mg cm−2), whereas high catalyst loading exhibited the best performance on the ORR side. The sample heat-treated at 250 °C delivered the highest bi-functional oxygen evolution and reduction reaction activity (OER/ORR) thanks to its thin-holey nanosheet-like structure with higher nickel oxidation state at 250 °C. This work further helps to develop low-cost electrocatalyst development for metal-air batteries. Full article
(This article belongs to the Section Electrocatalysis)
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Open AccessArticle Characteristics of Vanadium-Based Coal Gasification Slag and the NH3-Selective Catalytic Reduction of NO
Catalysts 2018, 8(8), 327; https://doi.org/10.3390/catal8080327
Received: 8 July 2018 / Revised: 2 August 2018 / Accepted: 4 August 2018 / Published: 9 August 2018
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Abstract
In order to realize the resource utilization of coal gasification slag (CGS) and to effectively control the emission of nitrogen oxides (NOx) in coke oven gas, the effect of the reaction conditions and vanadium loading over the CGS catalysts was carried
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In order to realize the resource utilization of coal gasification slag (CGS) and to effectively control the emission of nitrogen oxides (NOx) in coke oven gas, the effect of the reaction conditions and vanadium loading over the CGS catalysts was carried out for the selective catalytic reduction (SCR) of NO by NH3. The various vanadium loaded CGS catalysts were prepared using impregnation methods. The addition of 1% vanadium to the CGS catalyst (V1/CGS) significantly enhanced the NO conversion at a wide temperature range of 180–290 °C. The catalysts were characterized by N2 adsorption/desorption, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, NH3-temperature programmed desorption, Inductively coupled plasma optical emission spectrometer (ICP-OES), thermo gravimetric analyses (TGA), Fourier Transform infrared spectroscopy (FTIR), Scanning electron microscope-Energy dispersive spectrometer (SEM-EDS), and X-ray powder diffraction (XRD). The experimental results show the following: That (1) the NO removal efficiency of the sample CGS3 was the best, and it could be up to 100% under the experimental conditions; (2) The NO removal efficiency of the catalysts was higher in the atmosphere with SO2 than that without SO2; (3) The XRD results indicated the active component of vanadium was homogeneously dispersed over CGS and the active component of catalyst was V2O5 according to the XPS results. In particular, the NH3-TPD spectra of the vanadium loaded CGS catalyst showed that vanadium produced more acid sites, and the Lewis acid sites on the vanadium species were the active sites for the catalytic reduction of NO at 240–290 °C. Full article
(This article belongs to the Section Biomass Catalysis)
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Open AccessArticle Modification to L-H Kinetics Model and Its Application in the Investigation on Photodegradation of Gaseous Benzene by Nitrogen-Doped TiO2
Catalysts 2018, 8(8), 326; https://doi.org/10.3390/catal8080326
Received: 11 July 2018 / Revised: 3 August 2018 / Accepted: 6 August 2018 / Published: 9 August 2018
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Abstract
In this paper, the Langmuir-Hinshelwood (L-H) model has been used to investigate the kinetics of photodegradation of gaseous benzene by nitrogen-doped TiO2 (N-TiO2) at 25 °C under visible light irradiation. Experimental results show that the photoreaction coefficient kpm increased
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In this paper, the Langmuir-Hinshelwood (L-H) model has been used to investigate the kinetics of photodegradation of gaseous benzene by nitrogen-doped TiO2 (N-TiO2) at 25 °C under visible light irradiation. Experimental results show that the photoreaction coefficient kpm increased from 3.992 × 10−6 mol·kg−1·s−1 to 11.55 × 10−6 mol·kg−1·s−1 along with increasing illumination intensity. However, the adsorption equilibrium constant KL decreased from 1139 to 597 m3·mol−1 when the illumination intensity increased from 36.7 × 104 lx to 75.1 × 104 lx, whereas it was 2761 m3·mol−1 in the absence of light. This is contrary to the fact that KL should be a constant if the temperature was fixed. This phenomenon can be attributed to the breaking of the adsorption-desorption equilibrium by photocatalytically decomposition. To compensate for the disequilibrium of the adsorption-desorption process, photoreaction coefficient kpm was introduced to the expression of KL and the compensation form was denoted as Km. KL is an indicator of the adsorption capacity of TiO2 while Km is only an indicator of the coverage ratio of TiO2 surface. The modified L-H model has been experimentally verified so it is expected to be used to predict the kinetics of the photocatalytic degradation of gaseous benzene. Full article
(This article belongs to the Special Issue Emerging Trends in TiO2 Photocatalysis and Applications)
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Open AccessArticle Study of Extraction and Enzymatic Properties of Cell-Envelope Proteinases from a Novel Wild Lactobacillus plantarum LP69
Catalysts 2018, 8(8), 325; https://doi.org/10.3390/catal8080325
Received: 17 July 2018 / Revised: 5 August 2018 / Accepted: 7 August 2018 / Published: 8 August 2018
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Abstract
Lactobacilli cell-envelope proteinases (CEPs) have been widely used in the development of new streams of blockbuster nutraceuticals because of numerous biopharmaceutical potentials; thus, the development of viable methods for CEP extraction and the improvement of extraction efficiency will promote their full-scale application. In
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Lactobacilli cell-envelope proteinases (CEPs) have been widely used in the development of new streams of blockbuster nutraceuticals because of numerous biopharmaceutical potentials; thus, the development of viable methods for CEP extraction and the improvement of extraction efficiency will promote their full-scale application. In this study, CEP from a novel wild Lactobacillus plantarum LP69 was released from cells by incubating in calcium-free buffer. The extraction conditions of CEP were optimized by response surface methodology with the enzyme activity and specific activity as the detective marker. The optimal extraction conditions were: time of 80 min, temperature of 39 °C and buffer pH of 6.5. Under these conditions, enzyme activity and specific activity were (23.94 ± 0.86) U/mL and (1.37 ± 0.03) U/mg, respectively, which were well matched with the predicted values (22.12 U/mL and 1.36 U/mg). Optimal activity of the crude CEP occurred at pH 8.0 and 40 °C. It is a metallopeptidase, activated by Ca2+, inhibited by Zn2+ and ethylene-diamine-tetra-acetic acid, and a serine proteinase which is inhibited by phenylmethylsulfonyl fluoride. Kinetic studies showed that CEP from LP69 could hydrolyze whey protein, lactoglobulin and casein. Our study improves the extraction efficiency of CEPs from LP69, providing the reference for their industrial development. Full article
(This article belongs to the Special Issue Biocatalysts: Design and Application)
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Open AccessReview Morphology-Controlled Nitrogen-Containing Polymers as Synthetic Precursors for Electrochemical Oxygen Reduction Fe/N/C Cathode Catalysts
Catalysts 2018, 8(8), 324; https://doi.org/10.3390/catal8080324
Received: 2 July 2018 / Revised: 26 July 2018 / Accepted: 6 August 2018 / Published: 8 August 2018
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Abstract
Nitrogen-containing aromatic polymers such as polyimide are known for their high thermal stability. While they have been widely used in industry, their relevance to catalysis is still quite limited. In recent years, nitrogen-containing polymers have been explored as precursors of nitrogen-doped carbonaceous materials,
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Nitrogen-containing aromatic polymers such as polyimide are known for their high thermal stability. While they have been widely used in industry, their relevance to catalysis is still quite limited. In recent years, nitrogen-containing polymers have been explored as precursors of nitrogen-doped carbonaceous materials, which are particularly attractive as non-precious metal catalysts for oxygen reduction in fuel cells. The high thermal stability of nitrogen-containing polymers contributes to an effective control over the morphology of the resulting carbonaceous catalysts. This review article provides an overview of the recent progress on the research and development of Fe/N/C oxygen reduction catalysts prepared from morphology-controlled nitrogen-containing polymers. Full article
(This article belongs to the Special Issue Recent Advances of Electrocatalysis in Fuel Cells)
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Open AccessArticle Morphologically Tunable MnO2 Nanoparticles Fabrication, Modelling and Their Influences on Electrochemical Sensing Performance toward Dopamine
Catalysts 2018, 8(8), 323; https://doi.org/10.3390/catal8080323
Received: 4 July 2018 / Revised: 3 August 2018 / Accepted: 6 August 2018 / Published: 8 August 2018
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Abstract
The morphology or shape of nanomaterials plays an important role in functional applications, especially in the electrochemical sensing performance of nanocomposites modified electrodes. Herein, the morphology-dependent electrochemical sensing properties of MnO2-reduced graphene oxide/glass carbon electrode (MnO2-RGO/GCE) toward dopamine detection
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The morphology or shape of nanomaterials plays an important role in functional applications, especially in the electrochemical sensing performance of nanocomposites modified electrodes. Herein, the morphology-dependent electrochemical sensing properties of MnO2-reduced graphene oxide/glass carbon electrode (MnO2-RGO/GCE) toward dopamine detection were investigated. Firstly, various morphologies of nanoscale MnO2, including MnO2 nanowires (MnO2 NWs), MnO2 nanorods (MnO2 NRs), and MnO2 nanotubes (MnO2 NTs), were synthesized under different hydrothermal conditions. Then the corresponding MnO2-RGO/GCEs were fabricated via drop-casting and the subsequent electrochemical reduction method. The oxidation peak currents increase with the electrochemical activity area following the order of MnO2 NWs-RGO/GCE, MnO2 NTs-RGO/GCE, and MnO2 NRs-RGO/GCE. The spatial models for MnO2 NWs, MnO2 NTs, and MnO2 NRs are established and accordingly compared by their specific surface area, explaining well the evident difference in electrochemical responses. Therefore, the MnO2 NWs-RGO/GCE is selected for dopamine detection due to its better electrochemical sensing performance. The response peak current is found to be linear with dopamine concentration in the range of 8.0 × 10−8 mol/L–1.0 × 10−6 mol/L and 1.0 × 10−6 mol/L–8.0 × 10−5 mol/L with a lower detection limit of 1 × 10−9 mol/L (S/N = 3). Finally, MnO2 NWs-RGO/GCE is successfully used for the determination of dopamine injection samples, with a recovery of 99.6–103%. These findings are of great significance for understanding the relationship between unlimited nanoparticle structure manipulation and performance improvement. Full article
(This article belongs to the Section Electrocatalysis)
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Open AccessArticle Oxidative Steam Reforming of Raw Bio-Oil over Supported and Bulk Ni Catalysts for Hydrogen Production
Catalysts 2018, 8(8), 322; https://doi.org/10.3390/catal8080322
Received: 25 July 2018 / Revised: 5 August 2018 / Accepted: 6 August 2018 / Published: 8 August 2018
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Abstract
Several Ni catalysts of supported (on La2O3-αAl2O3, CeO2, and CeO2-ZrO2) or bulk types (Ni-La perovskites and NiAl2O4 spinel) have been tested in the oxidative steam reforming
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Several Ni catalysts of supported (on La2O3-αAl2O3, CeO2, and CeO2-ZrO2) or bulk types (Ni-La perovskites and NiAl2O4 spinel) have been tested in the oxidative steam reforming (OSR) of raw bio-oil, and special attention has been paid to the catalysts’ regenerability by means of studies on reaction-regeneration cycles. The experimental set-up consists of two units in series, for the separation of pyrolytic lignin in the first step (at 500 °C) and the on line OSR of the remaining oxygenates in a fluidized bed reactor at 700 °C. The spent catalysts have been characterized by N2 adsorption-desorption, X-ray diffraction and temperature programmed reduction, and temperature programmed oxidation (TPO). The results reveal that among the supported catalysts, the best balance between activity-H2 selectivity-stability corresponds to Ni/La2O3-αAl2O3, due to its smaller Ni0 particle size. Additionally, it is more selective to H2 than perovskite catalysts and more stable than both perovskites and the spinel catalyst. However, the activity of the bulk NiAl2O4 spinel catalyst can be completely recovered after regeneration by coke combustion at 850 °C because the spinel structure is completely recovered, which facilitates the dispersion of Ni in the reduction step prior to reaction. Consequently, this catalyst is suitable for the OSR at a higher scale in reaction-regeneration cycles. Full article
(This article belongs to the Special Issue Catalysis in Steam Reforming)
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Open AccessArticle Laccase Activity as an Essential Factor in the Oligomerization of Rutin
Catalysts 2018, 8(8), 321; https://doi.org/10.3390/catal8080321
Received: 9 July 2018 / Revised: 24 July 2018 / Accepted: 3 August 2018 / Published: 6 August 2018
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Abstract
The enzyme-mediated polymerization of bioactive phenolic compounds, such as the flavonoid rutin, has gained interest due to the enhanced physico-chemical and biological properties of the products, which increases their potential application as a nutraceutical. In this work, the influence of enzyme activity on
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The enzyme-mediated polymerization of bioactive phenolic compounds, such as the flavonoid rutin, has gained interest due to the enhanced physico-chemical and biological properties of the products, which increases their potential application as a nutraceutical. In this work, the influence of enzyme activity on rutin oligomerization was evaluated in reactions with low (1000 U/L) and high (10,000 U/L) initial laccase activities. For both reactions, high molecular weight oligomer fractions showed better properties compared to lower weight oligomers. Products of the reaction with low laccase activity exhibited thermal stability and antioxidant potential similar to control reaction, but led to higher inhibitory activity of xanthine oxidase and apparent aqueous solubility. Oligomers obtained in the reaction with high laccase activity showed better apparent aqueous solubility but decreased biological activities and stability. Their low antioxidant activity was correlated with a decreased phenolic content, which could be attributed to the formation of several bonds between rutin molecules. Full article
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Open AccessArticle Investigation of Earth-Abundant Oxygen Reduction Electrocatalysts for the Cathode of Passive Air-Breathing Direct Formate Fuel Cells
Catalysts 2018, 8(8), 320; https://doi.org/10.3390/catal8080320
Received: 30 June 2018 / Revised: 26 July 2018 / Accepted: 29 July 2018 / Published: 6 August 2018
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Abstract
The development of direct formate fuel cells encounters important obstacles related to the sluggish oxygen reduction reaction (ORR) and low tolerance to formate ions in Pt-based cathodes. In this study, electrocatalysts formed by earth-abundant elements were synthesized, and their activity and selectivity for
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The development of direct formate fuel cells encounters important obstacles related to the sluggish oxygen reduction reaction (ORR) and low tolerance to formate ions in Pt-based cathodes. In this study, electrocatalysts formed by earth-abundant elements were synthesized, and their activity and selectivity for the ORR were tested in alkaline electrolyte. The results showed that carbon-encapsulated iron-cobalt alloy nanoparticles and carbon-supported metal nitrides, characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD), do not present significant activity for the ORR, showing the same half-wave potential of Vulcan carbon. Contrarily, nitrogen-doped carbon, synthesized using imidazole as the nitrogen source, showed an increase in the half-wave potential, evidencing an influential role of nitrogen in the ORR electrocatalysis. The synthesis with the combination of Vulcan, imidazole, and iron or cobalt precursors resulted in the formation of nitrogen-coordinated iron (or cobalt) moieties, inserted in a carbon matrix, as revealed by X-ray absorption spectroscopy (XAS). Steady-state polarization curves for the ORR evidenced a synergistic effect between Fe and Co when these two metals were included in the synthesis (FeCo-N-C material), showing higher activity and higher limiting current density than the materials prepared only with Fe or Co. The FeCo-N-C material presented not only the highest activity for the ORR (approaching that of the state-of-the-art Pt/C) but also high tolerance to the presence of formate ions in the electrolyte. In addition, measurements with FeCo-N-C in the cathode of an passive air-breathing direct formate fuel cells, (natural diffusion of formate), showed peak power densities of 15.5 and 10.5 mW cm−2 using hydroxide and carbonate-based electrolytes, respectively, and high stability over 120 h of operation. Full article
(This article belongs to the Special Issue Recent Advances of Electrocatalysis in Fuel Cells)
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Open AccessArticle Investigation of Ni/SiO2 Fiber Catalysts Prepared by Different Methods on Hydrogen production from Ethanol Steam Reforming
Catalysts 2018, 8(8), 319; https://doi.org/10.3390/catal8080319
Received: 12 July 2018 / Revised: 31 July 2018 / Accepted: 2 August 2018 / Published: 4 August 2018
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Abstract
Ni/SiO2 (Ni/SF) catalysts were prepared by electrospinning of the SF followed by impregnation. The performance of the Ni/SF catalysts for hydrogen production from ethanol steam reforming at various conditions was investigated in comparison with a conventional Ni/silica porous (Ni/SP) catalyst. The influence
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Ni/SiO2 (Ni/SF) catalysts were prepared by electrospinning of the SF followed by impregnation. The performance of the Ni/SF catalysts for hydrogen production from ethanol steam reforming at various conditions was investigated in comparison with a conventional Ni/silica porous (Ni/SP) catalyst. The influence of the Ni/SF catalyst preparation methods on the catalytic activity and stability in ethanol steam reforming was also studied. The catalysts were prepared by three different preparation techniques: impregnation (IM), deposition precipitation (DP) and strong electrostatic adsorption (SEA). The Ni/SF catalyst exhibited higher performances and stability than the Ni/SP catalyst. The H2 yields of 55% and 47% were achieved at 600 °C using the Ni/SF and Ni/SP catalysts, respectively. The preparation methods had a significant effect on the catalytic activity and stability of the Ni/SF catalyst, where that prepared by the SEA method had a smaller Ni particle size and higher dispersion, and also exhibited the highest catalytic activity and stability compared to the Ni/SF catalysts prepared by IM and DP methods. The maximum H2 yield produced from the catalyst prepared by SEA was 65%, while that from the catalysts prepared by DP and IM were 60% and 55%, respectively, under the same conditions. The activity of the fiber catalysts prepared by SEA, DP and IM remained almost constant at all times during a 16 h stability test. Full article
(This article belongs to the Special Issue Catalysis in Steam Reforming)
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Open AccessArticle Catalytic Copyrolysis of Cork Oak and Waste Plastic Films over HBeta
Catalysts 2018, 8(8), 318; https://doi.org/10.3390/catal8080318
Received: 13 July 2018 / Revised: 30 July 2018 / Accepted: 1 August 2018 / Published: 3 August 2018
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Abstract
The catalytic fast copyrolysis (CFCP) of cork oak (CoOak) and waste plastic films (WPFs) over HBeta(25) (SiO2/Al2O3: 25) was investigated using a thermogravimetric (TG) analyzer and a tandem micro reactor-gas chromatography/mass spectrometry (TMR-GC/MS) to determine the effectiveness
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The catalytic fast copyrolysis (CFCP) of cork oak (CoOak) and waste plastic films (WPFs) over HBeta(25) (SiO2/Al2O3: 25) was investigated using a thermogravimetric (TG) analyzer and a tandem micro reactor-gas chromatography/mass spectrometry (TMR-GC/MS) to determine the effectiveness of WPFs as the hydrogen donating cofeeding feedstock on the CFCP of biomass. By applying CFCP, the maximum decomposition temperatures of CoOak (373.4 °C) and WPFs (487.9 °C) were reduced to 364.5 °C for CoOak and 436.5 °C for WPFs due to the effective interaction between the pyrolysis intermediates of CoOak and WPFs over HBeta(25), which has strong acidity and an appropriate pore size. The experimental yields of aromatic hydrocarbons on the CFCP of CoOak and WPFs were higher than their calculated yields concluded from the yields obtained from the individual catalytic fast pyrolysis (CFP) of CoOak and WPFs. The coke amount produced from the CFP of CoOak and WPFs over HBeta(25) were also decreased by applying CFCP. Full article
(This article belongs to the Special Issue Synthesis and Application of Zeolite Catalysts)
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Open AccessArticle Plasma Oxidation of H2S over Non-stoichiometric LaxMnO3 Perovskite Catalysts in a Dielectric Barrier Discharge Reactor
Catalysts 2018, 8(8), 317; https://doi.org/10.3390/catal8080317
Received: 12 July 2018 / Revised: 22 July 2018 / Accepted: 23 July 2018 / Published: 2 August 2018
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Abstract
In this work, plasma-catalytic removal of H2S over LaxMnO3 (x = 0.90, 0.95, 1, 1.05 and 1.10) has been studied in a coaxial dielectric barrier discharge (DBD) reactor. The non-stoichiometric effect of the LaxMnO3
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In this work, plasma-catalytic removal of H2S over LaxMnO3 (x = 0.90, 0.95, 1, 1.05 and 1.10) has been studied in a coaxial dielectric barrier discharge (DBD) reactor. The non-stoichiometric effect of the LaxMnO3 catalysts on the removal of H2S and sulfur balance in the plasma-catalytic process has been investigated as a function of specific energy density (SED). The integration of the plasma with the LaxMnO3 catalysts significantly enhanced the reaction performance compared to the process using plasma alone. The highest H2S removal of 96.4% and sulfur balance of 90.5% were achieved over the La0.90MnO3 catalyst, while the major products included SO2 and SO3. The missing sulfur could be ascribed to the sulfur deposited on the catalyst surfaces. The non-stoichiometric LaxMnO3 catalyst exhibited larger specific surface areas and smaller crystallite sizes compared to the LaMnO3 catalyst. The non-stoichiometric effect changed their redox properties as the decreased La/Mn ratio favored the transformation of Mn3+ to Mn4+, which contributed to the generation of oxygen vacancies on the catalyst surfaces. The XPS and H2-TPR results confirmed that the Mn-rich catalysts showed the higher relative concentration of surface adsorbed oxygen (Oads) and lower reduction temperature compared to LaMnO3 catalyst. The reaction performance of the plasma-catalytic oxidation of H2S is closely related to the relative concentration of Oads formed on the catalyst surfaces and the reducibility of the catalysts. Full article
(This article belongs to the Special Issue Plasma Catalysis)
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Open AccessArticle Photocatalytic Water Disinfection under Solar Irradiation by d-Glucose-Modified Titania
Catalysts 2018, 8(8), 316; https://doi.org/10.3390/catal8080316
Received: 18 July 2018 / Revised: 28 July 2018 / Accepted: 30 July 2018 / Published: 1 August 2018
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Abstract
Modified titania photocatalysts were synthesized by the pressure method using titanium(IV) oxide from Grupa Azoty Zakłady Chemiczne “Police” S.A., Police, Poland, and d-glucose solution. Characterization of obtained composites was performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), elemental analysis, and measurements
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Modified titania photocatalysts were synthesized by the pressure method using titanium(IV) oxide from Grupa Azoty Zakłady Chemiczne “Police” S.A., Police, Poland, and d-glucose solution. Characterization of obtained composites was performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), elemental analysis, and measurements of zeta potential and specific surface area (SSA). The possibility of using glucose-titania composites as photocatalysts for simulated solar-assisted disinfection against gram-negative Escherichia coli and gram-positive Stapchyloccocus epidermidis bacteria were examined in two reaction systems, i.e., for suspended and immobilized photocatalysts (on the concrete). It was found that an increase in the d-glucose concentration, i.e., higher carbon content, led to a decrease in antibacterial properties. The sample obtained from 1% of d-glucose solution at 100 °C (TiO2-1%-G-100) showed superior photocatalytic activity under UV-Vis irradiation toward both bacteria species. Water disinfection was more efficient for suspended photocatalyst than that for supported one, where complete disinfection was reached during 55–70 min and 120 min of irradiation, respectively. For the first time, it has been shown that titania modified with monosaccharides can be efficiently used for water disinfection, and the immobilization of photocatalyst on the concrete might be a prospective method for public water supplies. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessArticle Interface-Active Metal Organic Frameworks for Knoevenagel Condensations in Water
Catalysts 2018, 8(8), 315; https://doi.org/10.3390/catal8080315
Received: 5 July 2018 / Revised: 25 July 2018 / Accepted: 27 July 2018 / Published: 1 August 2018
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Abstract
It is desirable but challenging to locate solid catalysts at the oil-water interface to stabilize “Pickering emulsions”, which is one of the promising ways to develop efficient green chemical processes. Herein, water-stable metal organic framework ZIF-8 without any chemical modification was demonstrated to
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It is desirable but challenging to locate solid catalysts at the oil-water interface to stabilize “Pickering emulsions”, which is one of the promising ways to develop efficient green chemical processes. Herein, water-stable metal organic framework ZIF-8 without any chemical modification was demonstrated to be an interface-active catalyst for Knoevenagel condensation in a biphasic system. Pickering emulsion formed under the reaction conditions due to its amphiphilic property, which was beneficial to the mass transfer and led to high catalytic performance. Moreover, it can be repeatedly applied for Knoevenagel condensation for at least six successive cycles without losing its catalytic activity and framework integrity. Full article
(This article belongs to the Special Issue Catalysis by Metal-Organic Frameworks)
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Open AccessFeature PaperReview A Comparative Review on the Catalytic Mechanism of Nonheme Iron Hydroxylases and Halogenases
Catalysts 2018, 8(8), 314; https://doi.org/10.3390/catal8080314
Received: 17 July 2018 / Revised: 25 July 2018 / Accepted: 30 July 2018 / Published: 31 July 2018
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Abstract
Enzymatic halogenation and haloperoxidation are unusual processes in biology; however, a range of halogenases and haloperoxidases exist that are able to transfer an aliphatic or aromatic C–H bond into C–Cl/C–Br. Haloperoxidases utilize hydrogen peroxide, and in a reaction with halides (Cl/Br
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Enzymatic halogenation and haloperoxidation are unusual processes in biology; however, a range of halogenases and haloperoxidases exist that are able to transfer an aliphatic or aromatic C–H bond into C–Cl/C–Br. Haloperoxidases utilize hydrogen peroxide, and in a reaction with halides (Cl/Br), they react to form hypohalides (OCl/OBr) that subsequently react with substrate by halide transfer. There are three types of haloperoxidases, namely the iron-heme, nonheme vanadium, and flavin-dependent haloperoxidases that are reviewed here. In addition, there are the nonheme iron halogenases that show structural and functional similarity to the nonheme iron hydroxylases and form an iron(IV)-oxo active species from a reaction of molecular oxygen with α-ketoglutarate on an iron(II) center. They subsequently transfer a halide (Cl/Br) to an aliphatic C–H bond. We review the mechanism and function of nonheme iron halogenases and hydroxylases and show recent computational modelling studies of our group on the hectochlorin biosynthesis enzyme and prolyl-4-hydroxylase as examples of nonheme iron halogenases and hydroxylases. These studies have established the catalytic mechanism of these enzymes and show the importance of substrate and oxidant positioning on the stereo-, chemo- and regioselectivity of the reaction that takes place. Full article
(This article belongs to the Special Issue Quantum Chemical Modelling of Enzymatic Reactions)
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Open AccessFeature PaperReview Catalytic Transfer Hydrogenolysis as an Effective Tool for the Reductive Upgrading of Cellulose, Hemicellulose, Lignin, and Their Derived Molecules
Catalysts 2018, 8(8), 313; https://doi.org/10.3390/catal8080313
Received: 9 July 2018 / Revised: 27 July 2018 / Accepted: 28 July 2018 / Published: 31 July 2018
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Abstract
Lignocellulosic biomasses have a tremendous potential to cover the future demand of bio-based chemicals and materials, breaking down our historical dependence on petroleum resources. The development of green chemical technologies, together with the appropriate eco-politics, can make a decisive contribution to a cheap
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Lignocellulosic biomasses have a tremendous potential to cover the future demand of bio-based chemicals and materials, breaking down our historical dependence on petroleum resources. The development of green chemical technologies, together with the appropriate eco-politics, can make a decisive contribution to a cheap and effective conversion of lignocellulosic feedstocks into sustainable and renewable chemical building blocks. In this regard, the use of an indirect H-source for reducing the oxygen content in lignocellulosic biomasses and in their derived platform molecules is receiving increasing attention. In this contribution we highlight recent advances in the transfer hydrogenolysis of cellulose, hemicellulose, lignin, and of their derived model molecules promoted by heterogeneous catalysts for the sustainable production of biofuels and biochemicals. Full article
(This article belongs to the Special Issue Catalytic Processes for The Valorisation of Biomass Derived Molecules)
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Open AccessArticle Dehydrogenative Transformation of Alcoholic Substrates in Aqueous Media Catalyzed by an Iridium Complex Having a Functional Ligand with α-Hydroxypyridine and 4,5-Dihydro-1H-imidazol-2-yl Moieties
Catalysts 2018, 8(8), 312; https://doi.org/10.3390/catal8080312
Received: 29 June 2018 / Revised: 27 July 2018 / Accepted: 27 July 2018 / Published: 31 July 2018
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Abstract
A new catalytic system that employs water as an environmentally friendly solvent for the dehydrogenative oxidation of alcohols and lactonization of diols has been developed. In this catalytic system, a water-soluble dicationic iridium complex having a functional ligand that comprises α-hydroxypyridine and 4,5-dihydro-1
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A new catalytic system that employs water as an environmentally friendly solvent for the dehydrogenative oxidation of alcohols and lactonization of diols has been developed. In this catalytic system, a water-soluble dicationic iridium complex having a functional ligand that comprises α-hydroxypyridine and 4,5-dihydro-1H-imidazol-2-yl moieties exhibits high catalytic performance. For example, the catalytic dehydrogenative oxidation of 1-phenylethanol in the presence of 0.25 mol % of the iridium catalyst and base under reflux in water proceeded to give acetophenone in 92% yield. Additionally, under similar reaction conditions, the iridium-catalyzed dehydrogenative lactonization of 1,2-benzenedimethanol gave phthalide in 98% yield. Full article
(This article belongs to the Special Issue Reactions in Water and in Micelles)
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Open AccessFeature PaperArticle The Low Temperature Solvent-Free Aerobic Oxidation of Cyclohexene to Cyclohexane Diol over Highly Active Au/Graphite and Au/Graphene Catalysts
Catalysts 2018, 8(8), 311; https://doi.org/10.3390/catal8080311
Received: 2 July 2018 / Revised: 26 July 2018 / Accepted: 28 July 2018 / Published: 31 July 2018
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Abstract
The selectivity and activity of gold-catalysts supported on graphite and graphene have been compared in the oxidation of cyclohexene. These catalysts were prepared via impregnation and sol immobilisation methods, and tested using solventless and radical initiator-free reaction conditions. The selectivity of these catalysts
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The selectivity and activity of gold-catalysts supported on graphite and graphene have been compared in the oxidation of cyclohexene. These catalysts were prepared via impregnation and sol immobilisation methods, and tested using solventless and radical initiator-free reaction conditions. The selectivity of these catalysts has been directed towards cyclohexene epoxide using WO3 as a co-catalyst and further to cyclohexane diol by the addition of water, achieving a maximum selectivity of 17% to the diol. The sol immobilisation catalysts were more reproducible and far more active, however, selectivity towards the diol was lower than for the impregnation catalyst. The results suggest that formation of cyclohexane diol through solventless oxidation of cyclohexene is limited by a number of factors, such as the formation of an allylic hydroperoxyl species as well as the amount of in situ generated water. Full article
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