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Catalysts, Volume 9, Issue 12 (December 2019) – 102 articles

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Cover Story (view full-size image) Zeolite regeneration, which is aimed at eliminating coke trapped within micropores, is achieved [...] Read more.
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Open AccessArticle
Selective Conversion of Glucose to 5-Hydroxymethylfurfural by Using L-Type Zeolites with Different Morphologies
Catalysts 2019, 9(12), 1073; https://doi.org/10.3390/catal9121073 - 16 Dec 2019
Viewed by 364
Abstract
In the present work, the morphology of L-type zeolite (LTL topology) has been modified in order to evaluate the influence of several protonated-form LTL-zeolites with different morphologies on their stability and catalytic performance in the conversion of glucose into 5-hydroxymethylfurfural (5-HMF). Physico-chemical characterization [...] Read more.
In the present work, the morphology of L-type zeolite (LTL topology) has been modified in order to evaluate the influence of several protonated-form LTL-zeolites with different morphologies on their stability and catalytic performance in the conversion of glucose into 5-hydroxymethylfurfural (5-HMF). Physico-chemical characterization of the LTL-based catalysts has revealed that the three types of morphologies (needle, short rod and cylinder) are active, providing complete glucose conversion and high 5-HMF yield values. The addition of CaCl2 had a positive influence on the catalytic performance. It was found that morphology influences the textural and acid properties of LTL-zeolites, and hence their catalytic performance. The best catalytic results have been obtained with the NEEDLE-LTL, showing nanoparticles with a length of 4.46 μm and a width of 0.63 μm, which attains a 5-HMF yield of 63%, at 175 °C after 90 min of reaction, and a glucose conversion of 88%. The reusability study has revealed a progressive decrease in 5-HMF yield after each catalytic cycle. Different regeneration methods have been essayed without recovering the initial catalytic activity. The presence of organic molecules in micropores has been demonstrated by TG analysis, which are difficult to remove even after a regeneration process at 550 °C. Full article
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Open AccessArticle
The Formation Mechanism and Model of the Surface Nanoscale Kirkendall Effect on Au Catalyst Island/GaAs Substrate by Thermal Vapor-Liquid-Solid Method with Two-Step Temperature Mode
Catalysts 2019, 9(12), 1072; https://doi.org/10.3390/catal9121072 - 16 Dec 2019
Viewed by 231
Abstract
The Surface Nanoscale Kirkendall Effect is an important part of the Kirkendall effect, and has special role in the formation of surface nano material configurations. It can also cause faults in interconnection contact systems, yet this kind of effect has not yet been [...] Read more.
The Surface Nanoscale Kirkendall Effect is an important part of the Kirkendall effect, and has special role in the formation of surface nano material configurations. It can also cause faults in interconnection contact systems, yet this kind of effect has not yet been identified and studied in detail. Based on the obtained experimental results, this paper proposes a formation mechanism and model of the mixed-surface nanoscale Kirkendall effect formed by the role of Au metal catalyst islands/strips on a GaAs surface using the thermal Vapor-Liquid-Solid method. The diffusion of Ga, As, O atoms and the absorption of O atoms from a low-vacuum ambient into Au droplets forming surface nanoscale Au/Ga/O clusters leaves behind vacancies and voids; this process results in the nanoscale Kirkendall effect. In addition, the outward diffusion of the surface nanoscale Au/Ga/O clusters leaving behind bare GaAs holes in place of the former Au island forms the surface Kirkendall effect. Consequently, the combination of the two mentioned effects forms a new kind of KE, the so-called Surface Nanoscale Kirkendall Effect. This effect is generated either partly or completely, depending on the technological conditions. Accompanying this effect, the different configurations of nanomaterials have grown in number. The outward diffusion of surface nanoscale Au/Ga/O clusters was caused by the concentration of surface cluster gradients, the weakening of chemical bonds due to the accumulation of vacancies, the porosity, and pit-etching beneath the Au island. The diffusivity of surface Au/Ga/O clusters is numerically estimated. Its values vary from 2 × 10−10 to 10−11 m2/s. Potential applications of the surface nanoscale Kirkendall effect, making use of its advantages, limitations and disadvantages, are also discussed and proposed. Full article
(This article belongs to the Section Nanostructured Catalysts)
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Open AccessArticle
Electric Field Promoted Complete Oxidation of Benzene over PdCexCoy Catalysts at Low Temperature
Catalysts 2019, 9(12), 1071; https://doi.org/10.3390/catal9121071 - 16 Dec 2019
Viewed by 276
Abstract
The application of electric field promotes benzene oxidation significantly over Pd/CoxCey catalysts. For 1% Pd loading catalysts, the complete oxidation of benzene can be realized at 175 °C with an electric field under an input current of 3 mA, 79 [...] Read more.
The application of electric field promotes benzene oxidation significantly over Pd/CoxCey catalysts. For 1% Pd loading catalysts, the complete oxidation of benzene can be realized at 175 °C with an electric field under an input current of 3 mA, 79 °C lower than the temperature demanded for complete benzene conversion without electric field. The introduction of electric field can save Pd loading in the catalysts while maintaining high benzene conversion. The characterization experiments showed that CeO2 reduction was accelerated with electric field and created more active oxygen, promoting the formation of active sites on the catalyst surface. The OH removal ability of PdO was enhanced by forming CoO(OH) species, which can easily dehydroxylate since the reduction of Co3+ was promoted by the electric field. The optimized Ce/Co ratio is a balance between oxygen availability and OH removal ability. Full article
(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)
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Open AccessArticle
Niobium Oxide Catalysts as Emerging Material for Textile Wastewater Reuse: Photocatalytic Decolorization of Azo Dyes
Catalysts 2019, 9(12), 1070; https://doi.org/10.3390/catal9121070 - 14 Dec 2019
Viewed by 345
Abstract
Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the [...] Read more.
Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the developing areas of Northeast Brazil, which receives over 22 MJ m2 of natural sunlight irradiation annually. The application of photocatalytic treatment could incentivize water reuse practices in small and mid-sized textile businesses in the region. This work reports the facile synthesis of Nb2O5 catalysts and explores their performance for the treatment of colored azo dye effluents. The high photoactivity of this alternative photocatalyst makes it possible to quickly obtain complete decolorization, in less than 40 min of treatment. The optimal operational conditions are defined as 1.0 g L−1 Nb2O5 loading in slurry, 0.2 M of H2O2, pH 5.0 to treat up to 15 mg L−1 of methyl orange solution. To evaluate reutilization without photocatalytic activity loss, the Nb2O5 was recovered after the experience and reused, showing the same decolorization rate after several cycles. Therefore, Nb2O5 appears to be a promising photocatalytic material with potential applicability in wastewater treatment due to its innocuous character and high stability. Full article
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Open AccessFeature PaperArticle
Catalytic Dry Reforming and Cracking of Ethylene for Carbon Nanofilaments and Hydrogen Production Using a Catalyst Derived from a Mining Residue
Catalysts 2019, 9(12), 1069; https://doi.org/10.3390/catal9121069 - 14 Dec 2019
Viewed by 318
Abstract
In this study, iron-rich mining residue (UGSO) was used as a support to prepare a new Ni-based catalyst via a solid-state reaction protocol. Ni-UGSO with different Ni weight percentages wt.% (5, 10, and 13) were tested for C2H4 dry reforming [...] Read more.
In this study, iron-rich mining residue (UGSO) was used as a support to prepare a new Ni-based catalyst via a solid-state reaction protocol. Ni-UGSO with different Ni weight percentages wt.% (5, 10, and 13) were tested for C2H4 dry reforming (DR) and catalytic cracking (CC) after activation with H2. The reactions were conducted in a differential fixed-bed reactor at 550–750 °C and standard atmospheric pressure, using 0.5 g of catalyst. Pure gases were fed at a molar ratio of C2H4/CO2 = 3 for the DR reaction and C2H4/Ar = 3 for the CC reaction. The flow rate is defined by a GHSV = 4800 mLSTP/h.gcat. The catalyst performance is evaluated by calculating the C2H4 conversion as well as carbon and H2 yields. All fresh, activated, and spent catalysts, as well as deposited carbon, were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), temperature programmed reduction (TPR), and thermogravimetric analysis (TGA). The results so far show that the highest carbon and H2 yields are obtained with Ni-UGSO 13% at 750 °C for the CC reaction and at 650 °C for the DR reaction. The deposited carbon was found to be filamentous and of various sizes (i.e., diameters and lengths). The analyses of the results show that iron is responsible for the growth of carbon nanofilaments (CNF) and nickel is responsible for the split of C–C bonds. In terms of conversion and yield efficiencies, the performance of the catalytic formulations tested is proven at least equivalent to other Ni-based catalyst performances described by the literature. Full article
(This article belongs to the Special Issue Catalysts for Syngas Production)
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Open AccessArticle
Aldol Condensation of Cyclohexanone and Furfural in Fixed-Bed Reactor
Catalysts 2019, 9(12), 1068; https://doi.org/10.3390/catal9121068 - 14 Dec 2019
Viewed by 329
Abstract
Aldol condensation reaction is usually catalysed using homogeneous catalysts. However, the heterogeneous catalysis offers interesting advantages and the possibility of cleaner biofuels production. Nowadays, one of the most used kinds of heterogeneous catalysts are hydrotalcites, which belong to a group of layered double [...] Read more.
Aldol condensation reaction is usually catalysed using homogeneous catalysts. However, the heterogeneous catalysis offers interesting advantages and the possibility of cleaner biofuels production. Nowadays, one of the most used kinds of heterogeneous catalysts are hydrotalcites, which belong to a group of layered double hydroxides. This paper describes the aldol condensation of cyclohexanone (CH) and furfural (F) using Mg/Al mixed oxides and rehydrated mixed oxides in order to compare the catalyst activity after calcination and rehydration, as well as the possibility of its regeneration. The catalysts were synthesized by calcination and subsequent rehydration of the laboratory-prepared and commercial hydrotalcites, with Mg:Al molar ratio of 3:1. Their structural and chemical properties were determined by several analytical methods (inductively coupled plasma analysis (ICP), X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), specific surface area (BET), thermogravimetric analysis (TGA), temperature programmed desorption (TPD)). F-CH aldol condensation was performed in a continuous fixed-bed reactor at 80 °C, CH:F = 5:1, WHSV 2 h−1. The rehydrated laboratory-prepared catalysts showed a 100% furfural conversion for more than 55 h, in contrast to the calcined ones (only 24 h). The yield of condensation products FCH and F2CH was up to 68% and 10%, respectively. Obtained results suggest that Mg/Al mixed oxides-based heterogeneous catalyst is suitable for use in the aldol condensation reaction of furfural and cyclohexanone in a fixed-bed reactor, which is an interesting alternative way to obtain biofuels from renewable sources. Full article
(This article belongs to the Section Biomass Catalysis)
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Open AccessArticle
Study on the Photocathodic Protection of Q235 Steel by CdIn2S4 Sensitized TiO2 Composite in Splash Zone
Catalysts 2019, 9(12), 1067; https://doi.org/10.3390/catal9121067 - 14 Dec 2019
Viewed by 319
Abstract
In this work, the photo-catalytic activity of TiO2 is considerably enhanced via sensitization with CdIn2S4, and its application for protecting Q235 from corrosion in splash zones is examined. TiO2 nanotube arrays (NTAs) are prepared on a flat [...] Read more.
In this work, the photo-catalytic activity of TiO2 is considerably enhanced via sensitization with CdIn2S4, and its application for protecting Q235 from corrosion in splash zones is examined. TiO2 nanotube arrays (NTAs) are prepared on a flat Ti substrate via two-step anodization. CdIn2S4 is deposited on the surface of TiO2 NTAs by hydrothermal reaction. TiO2 NTAs with enormous specific surface areas and large-diameter hollow nanostructures are found to benefit the immobilization of CdIn2S4. As a narrow band gap semiconductor, CdIn2S4 is able to extend the light absorption range of TiO2, and the construction of an n–n type hetero-junction accelerates the separation of carriers. Strong solar light, which accelerates the corrosion of Q235 in the splash zone area, is converted into the necessary condition for protecting Q235 from corrosion. In this work, TiO2 is sensitized with MoS2 microspheres (MoS2/TiO2 nanocomposites), which were prepared on a flat Ti substrate via a two-step anodization and hydrothermal method, sequentially. Full article
(This article belongs to the Special Issue TiO2 for Photocatalytic Applications)
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Open AccessArticle
Novel Nickel- and Magnesium-Modified Cenospheres as Catalysts for Dry Reforming of Methane at Moderate Temperatures
Catalysts 2019, 9(12), 1066; https://doi.org/10.3390/catal9121066 - 14 Dec 2019
Viewed by 314
Abstract
Cenospheres from coal fly ashes were used as support in the preparation of Ni–Mg catalysts for dry reforming of methane. These materials were characterized by means of XRD, H2-temperature-programmed reduction (H2-TPR), CO2-temperature-programmed desorption (CO2-TPD), and [...] Read more.
Cenospheres from coal fly ashes were used as support in the preparation of Ni–Mg catalysts for dry reforming of methane. These materials were characterized by means of XRD, H2-temperature-programmed reduction (H2-TPR), CO2-temperature-programmed desorption (CO2-TPD), and low-temperature nitrogen sorption techniques. The cenosphere-supported catalysts showed relatively high activity and good stability in the dry reforming of methane (DRM) at 700 °C. The catalytic performance of modified cenospheres was found to depend on both Ni and Mg content. The highest activity at 750 °C and 1 atm was observed for the catalyst containing 30 wt % Mg and 10, 20, and 30 wt % Ni, yielding to CO2 and CH4 conversions of around 95%. Full article
(This article belongs to the Special Issue Catalysts for Reforming of Methane)
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Open AccessArticle
Shapes Control of Bi2WO6 Nano-Structures as Photo-Fenton Catalysts for Pulping Wastewater Treatment
Catalysts 2019, 9(12), 1065; https://doi.org/10.3390/catal9121065 - 14 Dec 2019
Viewed by 251
Abstract
Bi2WO6 assembled by flower-like microspheres and nanosheets were controllably synthesized through a one-step hydrothermal approach. Multiple technologies, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis diffuse reflectance spectrum (UV–Vis), were carried out to characterize the as-synthesized samples. [...] Read more.
Bi2WO6 assembled by flower-like microspheres and nanosheets were controllably synthesized through a one-step hydrothermal approach. Multiple technologies, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis diffuse reflectance spectrum (UV–Vis), were carried out to characterize the as-synthesized samples. The photocatalytic efficiency of Bi2WO6 synthesized with a series of temperature and pH values shows different morphologies and photocatalytic properties. The photocatalyst (Bi2WO6) synthesized at 220 °C and pH of 7 exhibited the best photocatalytic performance, with the methylene blue (MB) degradation approaching 91.6% after reaction time of 60 min. Free radical capture experiments indicate that •OH is the primary reactive species in the methylene blue (MB) degradation reaction, h+ and •O2 contribute negligible influence, while the addition of H2O2 significantly improves the photocatalytic activity of Bi2WO6. Biodegraded poplar preconditioning refiner chemical alkaline peroxide mechanical pulp wastewater (PPW) was treated over Bi2WO6 under UV light (Bi2WO6/UV/H2O2); chemical oxygen demand (CODCr) and color degradation rate were 85.8% and 92.0%, respectively. These results show that Bi2WO6 semiconductors can be introduced as an efficient and stable photocatalyst for industry wastewater treatment. Full article
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Open AccessArticle
Biodiesel Production Using Bauxite in Low-Cost Solid Base Catalyst Precursors
Catalysts 2019, 9(12), 1064; https://doi.org/10.3390/catal9121064 - 13 Dec 2019
Viewed by 324
Abstract
Investigation was conducted on bauxite mixed with Li2CO3 as alkali metal catalysts for biodiesel production. Bauxite contains a high percentage of Si and Al compounds among products. Because of the high expense of commercial materials (SiO2, Al2 [...] Read more.
Investigation was conducted on bauxite mixed with Li2CO3 as alkali metal catalysts for biodiesel production. Bauxite contains a high percentage of Si and Al compounds among products. Because of the high expense of commercial materials (SiO2, Al2O3) that makes them not economical, the method was very recently improved by replacing commercial materials with Si and Al from bauxite. This is one of the easiest methods for preparing heterogeneous transesterification catalysts, through one-pot blending, grinding bauxite with Li2CO3, and heating at 800 °C for 4 h. The prepared solid-base alkali metal catalyst was characterized in terms of its physical and chemical properties using X-ray powder diffraction and field-emission scanning electron microscopy (FE-SEM). The optimal conditions for the transesterification procedure are to mix methanol oil by molar ratio 9:1, under 65 °C, with catalyst amount 3 wt.%. The procedure is suitable for transesterifying oil to fatty acid methyl ester in the 96% range. Full article
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Open AccessArticle
Catalytic Decomposition of Oleic Acid to Fuels and Chemicals: Roles of Catalyst Acidity and Basicity on Product Distribution and Reaction Pathways
Catalysts 2019, 9(12), 1063; https://doi.org/10.3390/catal9121063 - 13 Dec 2019
Viewed by 294
Abstract
The roles of catalyst acidity and basicity playing in catalytic conversion of oleic acid were studied in a fixed-bed micro-reactor at atmospheric pressure. The chemical compositions of the petroleum-like products were obtained and the reaction pathways of different catalysts are discussed. The metal [...] Read more.
The roles of catalyst acidity and basicity playing in catalytic conversion of oleic acid were studied in a fixed-bed micro-reactor at atmospheric pressure. The chemical compositions of the petroleum-like products were obtained and the reaction pathways of different catalysts are discussed. The metal oxides are suitable for upgrading oleic acid into organic liquid products (OLPs). Over 98% oxygen was removed when CaO, MgO, and TiO2 were implemented, whereas a minimum oxygen removal lower than 20% was obtained by using quartz. The oxygen removal was 73% by alumina; however, the light oil yield (to feed) and the valuable product yield received were the highest in all investigated catalysts. The hydrocarbons in OLPs, overwhelmingly presenting in the product, were found to be alkenes and cycloalkenes, followed by saturated hydrocarbons, and then aromatics lower than 4%. For Lewis acidic catalysts, higher acidity of the catalyst is beneficial to deoxygenation but also secondary cracking. CaO has higher dehydrogenation capability than MgO does. Full article
(This article belongs to the Special Issue Catalysis for the Production of Sustainable Fuels and Chemicals)
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Open AccessArticle
Biochar-Supported FeS/Fe3O4 Composite for Catalyzed Fenton-Type Degradation of Ciprofloxacin
Catalysts 2019, 9(12), 1062; https://doi.org/10.3390/catal9121062 - 13 Dec 2019
Viewed by 247
Abstract
The Fenton-type oxidation catalyzed by iron minerals is a cost-efficient and environment-friendly technology for the degradation of organic pollutants in water, but their catalytic activity needs to be enhanced. In this work, a novel biochar-supported composite containing both iron sulfide and iron oxide [...] Read more.
The Fenton-type oxidation catalyzed by iron minerals is a cost-efficient and environment-friendly technology for the degradation of organic pollutants in water, but their catalytic activity needs to be enhanced. In this work, a novel biochar-supported composite containing both iron sulfide and iron oxide was prepared, and used for catalytic degradation of the antibiotic ciprofloxacin through Fenton-type reactions. Dispersion of FeS/Fe3O4 nanoparticles was observed with scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). Formation of ferrous sulfide (FeS) and magnetite (Fe3O4) in the composite was validated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Ciprofloxacin (initial concentration = 20 mg/L) was completely degraded within 45 min in the system catalyzed by this biochar-supported magnetic composite at a dosage of 1.0 g/L. Hydroxyl radicals (·OH) were proved to be the major reactive species contributing to the degradation reaction. The biochar increased the production of ·OH, but decreased the consumption of H2O2, and helped transform Fe3+ into Fe2+, according to the comparison studies using the unsupported FeS/Fe3O4 as the catalyst. All the three biochars prepared by pyrolysis at different temperatures (400, 500 and 600 °C) were capable for enhancing the reactivity of the iron compound catalyst. Full article
(This article belongs to the Special Issue Novel Heterogeneous Catalysts for Advanced Oxidation Processes (AOPs))
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Open AccessArticle
Pd–Co Nanoparticles Supported on Calcined Mg–Fe Hydrotalcites for the Suzuki–Miyaura Reaction in Water with High Turnover Numbers
Catalysts 2019, 9(12), 1061; https://doi.org/10.3390/catal9121061 - 13 Dec 2019
Viewed by 290
Abstract
We reveal the Suzuki–Miyaura reaction catalyzed by a Pd–Co nanocatalyst supported by Mg–Fe–CHT (calcined hydrotalcites). A variety of boronic acids and aryl halides were transformed into functionalized biphenyls in excellent yields using water as a solvent. The reaction could proceed under mild conditions [...] Read more.
We reveal the Suzuki–Miyaura reaction catalyzed by a Pd–Co nanocatalyst supported by Mg–Fe–CHT (calcined hydrotalcites). A variety of boronic acids and aryl halides were transformed into functionalized biphenyls in excellent yields using water as a solvent. The reaction could proceed under mild conditions with a simple operation and high turnover numbers. The excellent catalytic activities are reasonably attributed to the Co-doping, which forms a Pd–Co alloy on the surface of CHT. Full article
(This article belongs to the Section Nanostructured Catalysts)
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Open AccessArticle
SnO2/Diatomite Composite Prepared by Solvothermal Reaction for Low-Cost Photocatalysts
Catalysts 2019, 9(12), 1060; https://doi.org/10.3390/catal9121060 - 13 Dec 2019
Viewed by 259
Abstract
Abundant contaminants in wastewater have a negative effect on the natural environment and ecology. Developing highly efficient photocatalysts is a practical strategy to solve the pollution issue. In order to prevent the agglomeration of SnO2 nanoparticles and improve the photocatalytic efficiency, porous [...] Read more.
Abundant contaminants in wastewater have a negative effect on the natural environment and ecology. Developing highly efficient photocatalysts is a practical strategy to solve the pollution issue. In order to prevent the agglomeration of SnO2 nanoparticles and improve the photocatalytic efficiency, porous diatomite is adopted as a low-cost template to load monodispersed SnO2 nanoparticles by solvothermal reaction and sintering method. Through adjusting the mass of reactants, monodispersed SnO2 nanoparticles (~15 nm) generated on diatomite template achieved the maximum specific surface area of 23.53 m2·g−1. When served as a photocatalyst for degrading rhodamine B (Rh B) and methylene blue (MB), the composite presents an excellent photocatalytic activity close to pure SnO2, and achieves the fast degradation of Rh B and MB dye in 60 min. The degradation process is in well agreement with the first-order kinetic equation. The superior photocatalytic performance of SnO2/diatomite composite is attributed to the physical adsorption of dye molecules on the pores of diatomite, and the superior photocatalytic activity of monodispersed SnO2 nanoparticles. Due to the low-cost of diatomite and the easy preparation of SnO2 nanoparticles, the SnO2/diatomite composite has a promising application prospect, even better than pure SnO2 photocatalyst. Full article
(This article belongs to the Section Environmental Catalysis)
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Open AccessArticle
Electrochemical Synthesis of Zirconium Pre-Catalysts for Homogeneous Ethylene Oligomerization
Catalysts 2019, 9(12), 1059; https://doi.org/10.3390/catal9121059 - 12 Dec 2019
Viewed by 384
Abstract
The catalytic activity of electrochemically synthesized zirconium carboxylates was studied in the process of ethylene oligomerization. Zirconium carboxylates were electrochemically synthesized directly from metallic zirconium and corresponding carboxylic acids (acetic, octanoic and lauric). A comprehensive study (element analysis, nuclear magnetic resonance (NMR) and [...] Read more.
The catalytic activity of electrochemically synthesized zirconium carboxylates was studied in the process of ethylene oligomerization. Zirconium carboxylates were electrochemically synthesized directly from metallic zirconium and corresponding carboxylic acids (acetic, octanoic and lauric). A comprehensive study (element analysis, nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy, powder X-ray diffraction (PXRD)) of the synthesized zirconium carboxylates showed that these species contain bidentate carboxylate moieties. It was shown that obtained zirconium carboxylates, in combination with Et3Al2Cl3 (Al/Zr = 20), have a moderate activity of (7.6–9.9) × 103 molC2H4⋅molZr−1⋅h−1 in terms of ethylene oligomerization (at T = 80 °C, p = 20 bar), leading to even-numbered C4–C10 linear alpha-olefins. Full article
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Open AccessFeature PaperArticle
Tailoring of Hydrotalcite-Derived Cu-Based Catalysts for CO2 Hydrogenation to Methanol
Catalysts 2019, 9(12), 1058; https://doi.org/10.3390/catal9121058 - 12 Dec 2019
Viewed by 356
Abstract
Ternary CuxZnyAlz catalysts were prepared using the hydrotalcite (HT) method. The influence of the atomic x:y:z ratio on the physico-chemical and catalytic properties under CO2 hydrogenation conditions was probed. The characterization data of [...] Read more.
Ternary CuxZnyAlz catalysts were prepared using the hydrotalcite (HT) method. The influence of the atomic x:y:z ratio on the physico-chemical and catalytic properties under CO2 hydrogenation conditions was probed. The characterization data of the investigated catalysts were obtained by XRF, XRD, BET, TPR, CO2-TPD, N2O chemisorption, SEM, and TEM techniques. In the “dried” catalyst, the typical structure of a hydrotalcite phase was observed. Although the calcination and subsequent reduction treatments determined a clear loss of the hydrotalcite structure, the pristine phase addressed the achievement of peculiar physico-chemical properties, also affecting the catalytic activity. Textural and surface effects induced by the zinc concentration conferred a very interesting catalyst performance, with a methanol space time yield (STY) higher than that of commercial systems operated under the same experimental conditions. The peculiar behavior of the hydrotalcite-like samples was related to a high dispersion of the active phase, with metallic copper sites homogeneously distributed among the oxide species, thereby ensuring a suitable activation of H2 and CO2 reactants for a superior methanol production. Full article
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Open AccessReview
Progress and Trend on the Regulation Methods for Nanozyme Activity and Its Application
Catalysts 2019, 9(12), 1057; https://doi.org/10.3390/catal9121057 - 12 Dec 2019
Viewed by 378
Abstract
Natural enzymes, such as biocatalysts, are widely used in biosensors, medicine and health, the environmental field, and other fields. However, it is easy for natural enzymes to lose catalytic activity due to their intrinsic shortcomings including a high purification cost, insufficient stability, and [...] Read more.
Natural enzymes, such as biocatalysts, are widely used in biosensors, medicine and health, the environmental field, and other fields. However, it is easy for natural enzymes to lose catalytic activity due to their intrinsic shortcomings including a high purification cost, insufficient stability, and difficulties of recycling, which limit their practical applications. The unexpected discovery of the Fe3O4 nanozyme in 2007 has given rise to tremendous efforts for developing natural enzyme substitutes. Nanozymes, which are nanomaterials with enzyme-mimetic catalytic activity, can serve as ideal candidates for artificial mimic enzymes. Nanozymes possess superiorities due to their low cost, high stability, and easy preparation. Although great progress has been made in the development of nanozymes, the catalytic efficiency of existing nanozymes is relatively low compared with natural enzymes. It is still a challenging task to develop nanozymes with a precise regulation of catalytic activity. This review summarizes the classification and various strategies for modulating the activity as well as research progress in the different application fields of nanozymes. Typical examples of the recent research process of nanozymes will be presented and critically discussed. Full article
(This article belongs to the Special Issue State of the Art and Future Trends in Nanostructured Biocatalysis)
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Open AccessArticle
Comparison of Direct and Mediated Electron Transfer for Bilirubin Oxidase from Myrothecium Verrucaria. Effects of Inhibitors and Temperature on the Oxygen Reduction Reaction
Catalysts 2019, 9(12), 1056; https://doi.org/10.3390/catal9121056 - 11 Dec 2019
Viewed by 312
Abstract
One of the processes most studied in bioenergetic systems in recent years is the oxygen reduction reaction (ORR). An important challenge in bioelectrochemistry is to achieve this reaction under physiological conditions. In this study, we used bilirubin oxidase (BOD) from Myrothecium verrucaria, [...] Read more.
One of the processes most studied in bioenergetic systems in recent years is the oxygen reduction reaction (ORR). An important challenge in bioelectrochemistry is to achieve this reaction under physiological conditions. In this study, we used bilirubin oxidase (BOD) from Myrothecium verrucaria, a subclass of multicopper oxidases (MCOs), to catalyse the ORR to water via four electrons in physiological conditions. The active site of BOD, the T2/T3 cluster, contains three Cu atoms classified as T2, T3α, and T3β depending on their spectroscopic characteristics. A fourth Cu atom; the T1 cluster acts as a relay of electrons to the T2/T3 cluster. Graphite electrodes were modified with BOD and the direct electron transfer (DET) to the enzyme, and the mediated electron transfer (MET) using an osmium polymer (OsP) as a redox mediator, were compared. As a result, an alternative resting (AR) form was observed in the catalytic cycle of BOD. In the absence and presence of the redox mediator, the AR direct reduction occurs through the trinuclear site (TNC) via T1, specifically activated at low potentials in which T2 and T3α of the TNC are reduced and T3β is oxidized. A comparative study between the DET and MET was conducted at various pH and temperatures, considering the influence of inhibitors like H2O2, F, and Cl. In the presence of H2O2 and F, these bind to the TNC in a non-competitive reversible inhibition of O2. Instead; Cl acts as a competitive inhibitor for the electron donor substrate and binds to the T1 site. Full article
(This article belongs to the Special Issue Immobilized Non-Precious Electrocatalysts for Advanced Energy Devices)
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Open AccessFeature PaperArticle
Highly Carbon-Resistant Y Doped NiO–ZrOm Catalysts for Dry Reforming of Methane
Catalysts 2019, 9(12), 1055; https://doi.org/10.3390/catal9121055 - 11 Dec 2019
Viewed by 335
Abstract
Yttrium-doped NiO–ZrOm catalyst was found to be novel for carbon resistance in the CO2 reforming of methane. Yttrium-free and -doped NiO–ZrOm catalysts were prepared by a one-step urea hydrolysis method and characterized by Brunauer-Emmett-Teller (BET), TPR-H2, CO2 [...] Read more.
Yttrium-doped NiO–ZrOm catalyst was found to be novel for carbon resistance in the CO2 reforming of methane. Yttrium-free and -doped NiO–ZrOm catalysts were prepared by a one-step urea hydrolysis method and characterized by Brunauer-Emmett-Teller (BET), TPR-H2, CO2-TPD, XRD, TEM and XPS. Yttrium-doped NiO–ZrOm catalyst resulted in higher interaction between Ni and ZrOm, higher distribution of weak and medium basic sites, and smaller Ni crystallite size, as compared to the Y-free NiO–ZrOm catalyst after reaction. The DRM catalytic tests were conducted at 700 °C for 8 h, leading to a significant decrease of activity and selectivity for the yttrium-doped NiO–ZrOm catalyst. The carbon deposition after the DRM reaction on yttrium-doped NiO–ZrOm catalyst was lower than on yttrium-free NiO–ZrOm catalyst, which indicated that yttrium could promote the inhibition of carbon deposition during the DRM process. Full article
(This article belongs to the Special Issue CO2 Capture, Utilization and Storage: Catalysts Design)
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Open AccessFeature PaperReview
Morphology- and Crystalline Composition-Governed Activity of Titania-Based Photocatalysts: Overview and Perspective
Catalysts 2019, 9(12), 1054; https://doi.org/10.3390/catal9121054 - 11 Dec 2019
Viewed by 441
Abstract
Titania photocatalysts have been intensively examined for both mechanism study and possible commercial applications for more than 30 years. Although various reports have already been published on titania, including comprehensive review papers, the morphology-governed activity, especially for novel nanostructures, has not been reviewed [...] Read more.
Titania photocatalysts have been intensively examined for both mechanism study and possible commercial applications for more than 30 years. Although various reports have already been published on titania, including comprehensive review papers, the morphology-governed activity, especially for novel nanostructures, has not been reviewed recently. Therefore, this paper presents novel, attractive, and prospective titania photocatalysts, including zero-, one-, two-, and three-dimensional titania structures. The 1D, 2D, and 3D titania structures have been mainly designed for possible applications, e.g., (i) continuous use without the necessity of particulate titania separation, (ii) efficient light harvesting (e.g., inverse opals), (iii) enhanced activity (fast charge carriers’ separation, e.g., 1D nanoplates and 2D nanotubes). It should be pointed out that these structures might be also useful for mechanism investigation, e.g., (i) 3D titania aerogels with gold either incorporated inside the 3D network or supported in the porosity, and (ii) titania mesocrystals with gold deposited either on basal or lateral surfaces, for the clarification of plasmonic photocatalysis. Moreover, 0D nanostructures of special composition and morphology, e.g., magnetic(core)–titania(shell), mixed-phase titania (anatase/rutile/brookite), and faceted titania NPs have been presented, due to their exceptional properties, including easy separation in the magnetic field, high activity, and mechanism clarification, respectively. Although anatase has been usually thought as the most active phase of titania, the co-existence of other crystalline phases accelerates the photocatalytic activity significantly, and thus mixed-phase titania (e.g., famous P25) exhibits high photocatalytic activity for both oxidation and reduction reactions. It is believed that this review might be useful for the architecture design of novel nanomaterials for broad and diverse applications, including environmental purification, energy conversion, synthesis and preparation of “intelligent” surfaces with self-cleaning, antifogging, and antiseptic properties. Full article
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Open AccessFeature PaperArticle
Cu(II) and Fe(III) Complexes Derived from N-Acetylpyrazine-2-Carbohydrazide as Efficient Catalysts Towards Neat Microwave Assisted Oxidation of Alcohols
Catalysts 2019, 9(12), 1053; https://doi.org/10.3390/catal9121053 - 11 Dec 2019
Viewed by 388
Abstract
The mononuclear Cu(II) complex [Cu((kNNO-HL)(H2O)2] (1) was synthesized using N-acetylpyrazine-2-carbohydrazide (H2L) and characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray crystallography. Two Fe(III) complexes derived from the [...] Read more.
The mononuclear Cu(II) complex [Cu((kNNO-HL)(H2O)2] (1) was synthesized using N-acetylpyrazine-2-carbohydrazide (H2L) and characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray crystallography. Two Fe(III) complexes derived from the same ligand viz, mononuclear [Fe((kNNO-HL)Cl2] (2) and the binuclear [Fe(kNNO-HL)Cl(μ-OMe)]2 (3) (synthesized as reported earlier), were also used in this study. The catalytic activity of these three complexes (13) was examined towards the oxidation of alcohols using tert-butyl hydroperoxide (TBHP) as oxidising agent under solvent-free microwave irradiation conditions. Primary and secondary benzyl alcohols (benzyl alcohol and 1-phenylethanol), and secondary aliphatic alcohols (cyclohexanol) were used as model substrates for this study. A comparison of their catalytic efficiency was performed. Complex 1 exhibited the highest activity in the presence of TEMPO as promoter for the oxidation of 1-phenylethanol with a maximum yield of 91.3% of acetophenone. Full article
(This article belongs to the Special Issue Coordination Chemistry and Catalysis)
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Open AccessArticle
Synthesis of Hydroxy Sodalite from Coal Fly Ash for Biodiesel Production from Waste-Derived Maggot Oil
Catalysts 2019, 9(12), 1052; https://doi.org/10.3390/catal9121052 - 11 Dec 2019
Viewed by 317
Abstract
Zeolites are aluminosilicate crystalline materials known for their unique characteristics, and have been prominent for nearly half a century due to their wide and important industrial applications. The production of zeolites, however, remains a challenge due to the high cost of commercial reagents [...] Read more.
Zeolites are aluminosilicate crystalline materials known for their unique characteristics, and have been prominent for nearly half a century due to their wide and important industrial applications. The production of zeolites, however, remains a challenge due to the high cost of commercial reagents conventionally used as feedstocks. In the current study, hydroxy sodalite (HS) zeolite samples were synthesised from coal fly ash feedstock by a direct hydrothermal synthesis method. The effects of hydrothermal crystallisation synthesis time on phase crystallinity, crystal size, and morphology of the formed HS were investigated. The prepared samples were characterised using XRD, SEM, EDS and FT-IR techniques. The XRD results of the samples prepared with varying synthesis times confirmed the formation of HS from low to high phase purity and crystallinity from 11 to over 98%. The SEM results reflected gradual variation in crystal morphology, of which highly crystalline HS samples were associated with hexagonal-cubic and cubic-platelet crystals. The FTIR, depicting zeolite characteristics of T–O and T–O–T stretching vibrations in the molecular framework, further confirmed the formation of HS zeolites for samples obtained above the 24-h synthesis time. These zeolite samples were then evaluated for their catalytic activities in the conversion of maggot oil to biodiesel. The application of the various hydroxy sodalite samples for the transesterification of maggot oil yielded up to 84.10% biodiesel (FAME) with physicochemical properties that were in compliance with the biodiesel specification standards. This study investigated the novel use of a coal fly ash-derived, heterogeneous HS catalyst in biodiesel production from maggot oil, and indicates its potential to enhance biodiesel yield and quality upon process optimisation tests. Full article
(This article belongs to the Special Issue Catalytic and Functional Materials for Environment and Energy)
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Open AccessFeature PaperArticle
Hydroprocessing of Oleic Acid for Production of Jet-Fuel Range Hydrocarbons over Cu and FeCu Catalysts
Catalysts 2019, 9(12), 1051; https://doi.org/10.3390/catal9121051 - 11 Dec 2019
Viewed by 358
Abstract
In the present study, a series of monometallic Cu/SiO2-Al2O3 catalysts exhibited immense potential in the hydroprocessing of oleic acid to produce jet-fuel range hydrocarbons. The synergistic effect of Fe on the monometallic Cu/SiO2-Al2O3 [...] Read more.
In the present study, a series of monometallic Cu/SiO2-Al2O3 catalysts exhibited immense potential in the hydroprocessing of oleic acid to produce jet-fuel range hydrocarbons. The synergistic effect of Fe on the monometallic Cu/SiO2-Al2O3 catalysts of variable Cu loadings (5–15 wt%) was ascertained by varying Fe contents in the range of 1–5 wt% on the optimized 13% Cu/SiO2-Al2O3 catalyst. At 340 °C and 2.07 MPa H2 pressure, the jet-fuel range hydrocarbons yield and selectivities of 51.8% and 53.8%, respectively, were recorded for the Fe(3)-Cu(13)/SiO2-Al2O3 catalyst. To investigate the influence of acidity of support on the cracking of oleic acid, ZSM-5 (Zeolite Socony Mobil–5) and HZSM-5(Protonated Zeolite Socony Mobil–5)-supported 3% Fe-13% Cu were also evaluated at 300–340 °C and 2.07 MPa H2 pressure. Extensive techniques including N2 sorption analysis, pyridine- Fourier Transform Infrared Spectroscopy (Pyridine-FTIR), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and H2-Temperature Programmed Reduction (H2-TPR) analyses were used to characterize the materials. XPS analysis revealed the existence of Cu1+ phase in the Fe(3)-Cu(13)/SiO2-Al2O3 catalyst, while Cu metal was predominant in both the ZSM-5 and HZSM-5-supported FeCu catalysts. The lowest crystallite size of Fe(3)-Cu(13)/SiO2-Al2O3 was confirmed by XRD, indicating high metal dispersion and corroborated by the weakest metal–support interaction revealed from the TPR profile of this catalyst. CO chemisorption also confirmed high metal dispersion (8.4%) for the Fe(3)-Cu(13)/SiO2-Al2O3 catalyst. The lowest and mildest Brønsted/Lewis acid sites ratio was recorded from the pyridine–FTIR analysis for this catalyst. The highest jet-fuel range hydrocarbons yield of 59.5% and 73.6% selectivity were recorded for the Fe(3)-Cu(13)/SiO2-Al2O3 catalyst evaluated at 300 °C and 2.07 MPa H2 pressure, which can be attributed to its desirable textural properties, high oxophilic iron content, high metal dispersion and mild Brønsted acid sites present in this catalyst. Full article
(This article belongs to the Special Issue Catalysis for the Production of Sustainable Fuels and Chemicals)
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Open AccessArticle
Benchmarking Acidic and Basic Catalysis for a Robust Production of Biofuel from Waste Cooking Oil
Catalysts 2019, 9(12), 1050; https://doi.org/10.3390/catal9121050 - 10 Dec 2019
Viewed by 375
Abstract
The production of biodiesel at the industrial level is mainly based on the use of basic catalysts. Otherwise, also acidic catalysis allowed high conversion and yields, as this method is not affected by the percentage of free fatty acids present in the starting [...] Read more.
The production of biodiesel at the industrial level is mainly based on the use of basic catalysts. Otherwise, also acidic catalysis allowed high conversion and yields, as this method is not affected by the percentage of free fatty acids present in the starting sample. This work has been useful in assessing the possible catalytic pathways in the production of fatty acid methyl esters (FAMEs), starting from different cooking waste oil mixtures, exploring particularly acidic catalysis. It was possible to state that the optimal experimental conditions required concentrated sulfuric acid 20% w/w as a catalyst, a reaction time of twelve hours, a temperature of 85 °C and a molar ratio MeOH/oil of 6:1. The role of silica in the purification method was also explored. By evaluating the parameters, type of catalyst, temperature, reaction time and MeOH/oil molar ratios, it has been possible to develop a robust method for the production of biodiesel from real waste mixtures with conversions up to 99%. Full article
(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)
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Open AccessArticle
Removal of Banana Tree Fungi Using Green Tuff Rock Powder Waste Containing Zeolite
Catalysts 2019, 9(12), 1049; https://doi.org/10.3390/catal9121049 - 10 Dec 2019
Viewed by 329
Abstract
Hinai green tuff, which is found in Akita Prefecture, Japan, is used for the production of building materials, etc. About 60% of all stone is emitted as waste powder and therefore it is important to find ways for recycling it. In this work, [...] Read more.
Hinai green tuff, which is found in Akita Prefecture, Japan, is used for the production of building materials, etc. About 60% of all stone is emitted as waste powder and therefore it is important to find ways for recycling it. In this work, the characteristics of green tuff powder have been investigated. The results of scanning electron microscope (SEM) and elemental map observations indicate that the green tuff contains TiO2 on zeolite. The green tuff can therefore be used as a natural catalyst for producing hydrogen peroxide with moisture and oxygen with light. The optimum calcined temperature of the green tuff powder is about 800 °C, producing the hydroxyl radical from hydrogen peroxide decomposition without ultraviolet light (UV) and decomposition of the superoxide anion. As the application of green tuff powder, Cavendish banana trees found in the Philippines infected by a new Panama disease were treated with powder suspension in order to remove the fungus (a type of Fusarium wilt) due to the photocatalyst characteristics of powder. The suspension, prepared by using the powder was sprayed on the infected banana trees for about one month. Photograph observation indicated that the so-called 800 °C suspension spray was more effective in growing the infected banana trees. Full article
(This article belongs to the Special Issue Synthesis and Application of Zeolite Catalysts)
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Open AccessCommunication
Facile and Large-scale Synthesis of Defective Black TiO2−x(B) Nanosheets for Efficient Visible-light-driven Photocatalytic Hydrogen Evolution
Catalysts 2019, 9(12), 1048; https://doi.org/10.3390/catal9121048 - 10 Dec 2019
Viewed by 348
Abstract
In the work, we firstly report the facile and large-scale synthesis of defective black TiO2−x(B) nanosheets via a dual-zone NaBH4 reduction method. The structure, physico-chemical, and optical properties of TiO2−x(B) nanosheets were systematically characterized by powder X-ray diffraction, [...] Read more.
In the work, we firstly report the facile and large-scale synthesis of defective black TiO2−x(B) nanosheets via a dual-zone NaBH4 reduction method. The structure, physico-chemical, and optical properties of TiO2−x(B) nanosheets were systematically characterized by powder X-ray diffraction, Raman spectroscopy, UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy, etc. The concentration of Ti3+ can be well tuned by NaBH4 reduction. With increasing the mass ratio of NaBH4 to TiO2(B), the generation of Ti3+ defects gives rise to the increased intensity of a broad band absorption in the visible wavelength range. It is demonstrated that the TiO2−x(B) photocatalyst synthesized with the mass ratio of NaBH4 to TiO2(B) of 3:1 exhibited an optimum photocatalytic activity and excellent photostability for hydrogen evolution under visible-light irradiation. By combining the advantages of 2D TiO2(B) nanosheets architecture with those of Ti3+ self-doping and simultaneous production of oxygen vacancy sites, the enhanced photocatalytic performance of the defective TiO2−x(B) nanosheets was achieved. Full article
(This article belongs to the Special Issue TiO2 for Photocatalytic Applications)
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Open AccessArticle
Heterogeneous Nanomagnetic Catalyst from Cupriferous Mineral Processing Gangue for the Production of Biodiesel
Catalysts 2019, 9(12), 1047; https://doi.org/10.3390/catal9121047 - 10 Dec 2019
Viewed by 367
Abstract
The commercialisation of biodiesel as an alternative energy source is challenged by high production costs. The cost of feedstock, catalyst and separation of the dissolved catalyst (homogeneous catalyst) from the product are the major contributors to the total manufacturing cost of biodiesel. This [...] Read more.
The commercialisation of biodiesel as an alternative energy source is challenged by high production costs. The cost of feedstock, catalyst and separation of the dissolved catalyst (homogeneous catalyst) from the product are the major contributors to the total manufacturing cost of biodiesel. This study investigated the potential of a heterogeneous catalyst produced from mineral processing waste for biodiesel production. Tailings from the concentration of cupriferous minerals served as the starting material for synthesis of the catalyst. The nanomagnetic catalysts were prepared using co-precipitation (CMCO) and sol-gel (CMSG) methods, combined with zero-valent iron nanoparticles (ZVINPs) to form a hydride catalyst (CMSG/ZVINPs). Catalyst properties were assessed using SEM, TEM, BET and EDX. The catalyst activity was enhanced by a large number of basic sites that were afforded by the presence of calcite and magnesite. Good surface areas and particle sizes of 58.9 m2/g and 15.4 nm, and 52.6 m2/g and 16.9 nm were observed for the catalysts that were prepared using the CMSG and CMCO methods, respectively. 173 emu/g mass magnetisation was obtained for CMSG/ZVINPs, which was sufficient for the catalyst to be regenerated and reused for biodiesel production by exploiting the magnetic properties. The maximum yield obtained with this catalyst was 88% and an average of 27% decrease in biodiesel yield was observed after four reaction cycles. The physicochemical properties of the biodiesel produced complied with the ASTM standard specification. The results showed that mineral processing tailings are a viable starting material for catalyst preparation in biodiesel production. Full article
(This article belongs to the Special Issue Sustainable and Environmental Catalysis)
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Open AccessReview
Metal Complexes Containing Redox-Active Ligands in Oxidation of Hydrocarbons and Alcohols: A Review
Catalysts 2019, 9(12), 1046; https://doi.org/10.3390/catal9121046 - 09 Dec 2019
Viewed by 445
Abstract
Ligands are innocent when they allow oxidation states of the central atoms to be defined. A noninnocent (or redox) ligand is a ligand in a metal complex where the oxidation state is not clear. Dioxygen can be a noninnocent species, since it exists [...] Read more.
Ligands are innocent when they allow oxidation states of the central atoms to be defined. A noninnocent (or redox) ligand is a ligand in a metal complex where the oxidation state is not clear. Dioxygen can be a noninnocent species, since it exists in two oxidation states, i.e., superoxide (O2) and peroxide (O22−). This review is devoted to oxidations of C–H compounds (saturated and aromatic hydrocarbons) and alcohols with peroxides (hydrogen peroxide, tert-butyl hydroperoxide) catalyzed by complexes of transition and nontransition metals containing innocent and noninnocent ligands. In many cases, the oxidation is induced by hydroxyl radicals. The mechanisms of the formation of hydroxyl radicals from H2O2 under the action of transition (iron, copper, vanadium, rhenium, etc.) and nontransition (aluminum, gallium, bismuth, etc.) metal ions are discussed. It has been demonstrated that the participation of the second hydrogen peroxide molecule leads to the rapture of O–O bond, and, as a result, to the facilitation of hydroxyl radical generation. The oxidation of alkanes induced by hydroxyl radicals leads to the formation of relatively unstable alkyl hydroperoxides. The data on regioselectivity in alkane oxidation allowed us to identify an oxidizing species generated in the decomposition of hydrogen peroxide: (hydroxyl radical or another species). The values of the ratio-of-rate constants of the interaction between an oxidizing species and solvent acetonitrile or alkane gives either the kinetic support for the nature of the oxidizing species or establishes the mechanism of the induction of oxidation catalyzed by a concrete compound. In the case of a bulky catalyst molecule, the ratio of hydroxyl radical attack rates upon the acetonitrile molecule and alkane becomes higher. This can be expanded if we assume that the reactions of hydroxyl radicals occur in a cavity inside a voluminous catalyst molecule, where the ratio of the local concentrations of acetonitrile and alkane is higher than in the whole reaction volume. The works of the authors of this review in this field are described in more detail herein. Full article
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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Open AccessArticle
Passive Solar Photocatalytic Treatment of Emerging Contaminants in Water: A Field Study
Catalysts 2019, 9(12), 1045; https://doi.org/10.3390/catal9121045 - 09 Dec 2019
Viewed by 367
Abstract
Global economic shifts towards utilization of solar energy provides opportunities for photocatalytic technologies that can harness this abundant source of energy for treatment of organic contaminants. The majority of studies in this area have been performed under artificial light, whereas in this paper, [...] Read more.
Global economic shifts towards utilization of solar energy provides opportunities for photocatalytic technologies that can harness this abundant source of energy for treatment of organic contaminants. The majority of studies in this area have been performed under artificial light, whereas in this paper, the efficacy of passive photocatalysis was studied under sunlight. Buoyant titanium dioxide (TiO2) coated glass spheres were used to treat 2, 4-dichlorophenoxy acetic acid (2, 4-D), methyl chlorophenoxy propionic acid (MCPP), and 3, 6-Dichloro-2-methoxy benzoic acid (Dicamba) in Killex®, a commercially available herbicide. Furthermore, photocatalytic degradation of sulfolane and a typical naphthenic acid (cyclopentane carboxylic acid—CPA) were also tested under ambient conditions. The results showed 99.8% degradation of 2, 4-D, 100% degradation of both MCPP and Dicamba in Killex® solution, and 97.4% degradation of sulfolane by capturing 3.18 MJ/m2 solar energy. Total organic carbon (TOC) was decreased by 88% and 64% in both solutions, respectively. TOC of the aqueous solution containing 20 ppm CPA was also decreased by 78.4% with 7.8 MJ/m2 energy. Despite the slow kinetics and the temporal variations of sunlight in northern latitudes, the results indicated that passive photocatalysis is a promising approach for treatment of contaminants under ambient conditions. Full article
(This article belongs to the Special Issue State-of-the-Art Photocatalytical Technology in North America)
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Open AccessArticle
Advanced Ga2O3/Lignin and ZrO2/Lignin Hybrid Microplatforms for Glucose Oxidase Immobilization: Evaluation of Biosensing Properties by Catalytic Glucose Oxidation
Catalysts 2019, 9(12), 1044; https://doi.org/10.3390/catal9121044 - 09 Dec 2019
Viewed by 329
Abstract
In this study, novel Ga2O3/lignin and ZrO2/lignin hybrid materials were obtained and used as supports for the adsorption of the enzyme glucose oxidase (GOx). A biosensor system based on the hybrid supports was then designed to determine [...] Read more.
In this study, novel Ga2O3/lignin and ZrO2/lignin hybrid materials were obtained and used as supports for the adsorption of the enzyme glucose oxidase (GOx). A biosensor system based on the hybrid supports was then designed to determine the concentration of glucose in various solutions. The obtained bioinspired platforms were analyzed to determine chemical and physical properties of the support structures. A determination was made of the effectiveness of the proposed method of immobilization and the quality of operation of the constructed glucose biosensor in electrochemical tests. To characterize the materials, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), electrokinetic (zeta) potential measurements, atomic force microscopy (AFM), particle size measurements (NIBS technique), and elemental analysis (EA) were used. In further research, glucose oxidase (GOx) was immobilized on the surface of the obtained functional Ga2O3/lignin and ZrO2/lignin biomaterials. The best immobilization capacities—24.7 and 27.1 mg g−1 for Ga2O3/lignin and ZrO2/lignin, respectively—were achieved after a 24 h immobilization process. The Ga2O3/Lig/GOx and ZrO2/Lig/GOx systems were used for the construction of electrochemical biosensor systems, in a dedicated carbon paste electrode (CPE) with the addition of graphite and ferrocene. Full article
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