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Catalysts, Volume 9, Issue 8 (August 2019)

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Cover Story (view full-size image) In the paper by Orian et al. on page 679, the catalytic activity of anti- and syn-Rh/Cr indenyl [...] Read more.
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Open AccessArticle
Photocatalytic Removal of Harmful Algae in Natural Waters by Ag/[email protected] Coating under Sunlight
Catalysts 2019, 9(8), 698; https://doi.org/10.3390/catal9080698 - 20 Aug 2019
Viewed by 451
Abstract
In order to control the cyanobacterial blooms in eutrophic water, an Ag/[email protected] floating coating was prepared by a dip-coating method with a sponge, innovatively employed as a carrier for the removal of algae in natural water samples. The as-prepared photocatalyst was characterized by [...] Read more.
In order to control the cyanobacterial blooms in eutrophic water, an Ag/[email protected] floating coating was prepared by a dip-coating method with a sponge, innovatively employed as a carrier for the removal of algae in natural water samples. The as-prepared photocatalyst was characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (SEM). The effects of this Ag/[email protected] coating on algal removal and phytoplankton community structure in natural water samples with cyanobacterial blooms were investigated under sunlight. Results showed that Ag/[email protected] distributed uniformly on the surface of the coating with good stability and algae removal efficiency in water bodies. After 6 h of exposure under sunlight, the chlorophyll a in the natural water samples was degraded by 99.9%, the densities of Microcystis aeruginosa were reduced by 92.6% and the densities and biomass of the other algae decreased by about 80%. Meanwhile, the content of colored dissolved organic matter (CDOM) in the samples was decreased, effectively controlling the cyanobacterial blooms. It was found that O2•− played the main role in the photocatalytic inactivation. In conclusion, the Ag/[email protected] coating has a promising application potential for the removal of harmful cyanobacteria, and provides a new idea for the control of cyanobacterial blooms in water bodies. Full article
(This article belongs to the Section Environmental Catalysis)
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Open AccessArticle
Regarding the Nature of Charge Carriers Formed by UV or Visible Light Excitation of Carbon-Modified Titanium Dioxide
Catalysts 2019, 9(8), 697; https://doi.org/10.3390/catal9080697 - 20 Aug 2019
Viewed by 457
Abstract
Although titanium dioxide gathers many of the required properties for its application in photocatalytic processes, its lack of activity in the visible range is a major hurdle yet to be overcome. Among different strategies, the post-synthesis modification of TiO2 powders with organic [...] Read more.
Although titanium dioxide gathers many of the required properties for its application in photocatalytic processes, its lack of activity in the visible range is a major hurdle yet to be overcome. Among different strategies, the post-synthesis modification of TiO2 powders with organic compounds has already led to commercially available materials, such as KRONOClean 7000. In this work, we apply diffuse reflectance transient absorption spectroscopy on this visible-light active photocatalyst and study the dynamics of the charge carriers alternatively induced by UV or visible light laser irradiation, under inert or reactive atmospheres. Our results can be interpreted by considering the material as TiO2 sensitized by an organic-based layer, in agreement with previous studies on it, and show that the oxidative power of the material is considerably diminished under visible light irradiation. By complementarily performing continuous visible light irradiation photocatalysis experiments in aerated aqueous suspensions, we show that, although the oxidation of methanol proceeds at a very slow rate, the oxidation of chlorpromazine occurs much faster thanks to its better suited redox potential. Full article
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Open AccessArticle
Optimization of the Washcoat Slurry for Hydrotalcite-Based LNT Catalyst
Catalysts 2019, 9(8), 696; https://doi.org/10.3390/catal9080696 - 20 Aug 2019
Viewed by 367
Abstract
This work aimed to optimize the washcoat slurry for hydrotalcite-based lean NOx trap (LNT) catalyst. The effects of the slurry properties including pH, solid content, binder and additive on the hydrotalcite-based slurry viscosity were investigated. The particle size distribution of the optimal hydrotalcite-based [...] Read more.
This work aimed to optimize the washcoat slurry for hydrotalcite-based lean NOx trap (LNT) catalyst. The effects of the slurry properties including pH, solid content, binder and additive on the hydrotalcite-based slurry viscosity were investigated. The particle size distribution of the optimal hydrotalcite-based slurry was measured. A cordierite material was used to coat the optimal slurry, and the washcoat was characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption. The optimal slurry containing Pt and Ba was coated on the cordierite for the preparation of hydrotalcite-based LNT catalyst, and the performances of this catalyst were evaluated by NOx storage test, temperature programmed desorption and NOx reduction. For comparison, the performance of the commercial LNT catalyst with Pt/BaO/Al2O3 was analyzed. After coating, the hydrotalcite-based washcoat was closely contacted with the support, being the main phase MgO and presenting a specific surface area of 86.3 m2/g. The hydrotalcite-based LNT catalyst had better NOx storage and desorption ability, selectivity to N2 and LNT efficiency than the Pt/BaO/Al2O3 catalyst. Full article
(This article belongs to the Section Environmental Catalysis)
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Open AccessArticle
Influence of MoS2 on Activity and Stability of Carbon Nitride in Photocatalytic Hydrogen Production
Catalysts 2019, 9(8), 695; https://doi.org/10.3390/catal9080695 - 17 Aug 2019
Viewed by 491
Abstract
MoS2/C3N4 (MS-CN) composite photocatalysts have been synthesized by three different methods, i.e., in situ-photodeposition, sonochemical, and thermal decomposition. The crystal structure, optical properties, chemical composition, microstructure, and electron transfer properties were investigated by X-ray diffraction, UV-vis diffuse reflectance [...] Read more.
MoS2/C3N4 (MS-CN) composite photocatalysts have been synthesized by three different methods, i.e., in situ-photodeposition, sonochemical, and thermal decomposition. The crystal structure, optical properties, chemical composition, microstructure, and electron transfer properties were investigated by X-ray diffraction, UV-vis diffuse reflectance spectroyscopy, X-ray photoelectron spectroscopy, electron microscopy, photoluminescence, and in situ electron paramagnetic resonance spectroscopy. During photodeposition, the 2H MoS2 phase was formed upon reduction of [MoS4]2− by photogenerated conduction band electrons and then deposited on the surface of CN. A thin crystalline layer of 2H MoS2 formed an intimate interfacial contact with CN that favors charge separation and enhances the photocatalytic activity. The 2H MS-CN phase showed the highest photocatalytic H2 evolution rate (2342 μmol h−1 g−1, 25 mg catalyst/reaction) under UV-vis light irradiation in the presence of lactic acid as sacrificial reagent and Pt as cocatalyst. Full article
(This article belongs to the Special Issue Catalysts for Solar Fuels)
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Open AccessArticle
Mild Preoxidation Treatment of Pt/TiO2 Catalyst and Its Enhanced Low Temperature Formaldehyde Decomposition
Catalysts 2019, 9(8), 694; https://doi.org/10.3390/catal9080694 - 16 Aug 2019
Viewed by 419
Abstract
The typical platinum nanoparticles loaded on titania (Pt/TiO2) were pretreated with mild oxidation (<300 °C) in pure oxygen to enhance the low-temperature formaldehyde (HCHO) decomposition performance. The structural properties of support and platinum nanoparticles were characterized by X-ray diffraction (XRD), physical [...] Read more.
The typical platinum nanoparticles loaded on titania (Pt/TiO2) were pretreated with mild oxidation (<300 °C) in pure oxygen to enhance the low-temperature formaldehyde (HCHO) decomposition performance. The structural properties of support and platinum nanoparticles were characterized by X-ray diffraction (XRD), physical adsorption/desorption, high-resolution transmission electron microscopy (HRTEM), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFITS), and temperature-programmed reduction and oxidation (TPR and TPO). The catalytic results showed that the low temperature HCHO decomposition activity of mild pre-oxidized Pt/TiO2 was around three times that of the pristine one. According to the characterization results, the structure of the Pt/TiO2 support and their Pt particle sizes had negligible change after pre-oxidation treatment. The cationic Pt content of Pt/TiO2 and surface roughness of Pt nanoparticles gradually increased with the increasing temperature of the pre-oxidation treatment. Mild pre-oxidation treatment was beneficial to the oxygen activation and water dissociation of Pt/TiO2. In situ HCHO-DFIRTS results showed that the mild pre-oxidation treatment could enhance the dehydrogenation of formate. Full article
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Open AccessArticle
Fast Method for Testing the Photocatalytic Performance of Modified Gypsum
Catalysts 2019, 9(8), 693; https://doi.org/10.3390/catal9080693 - 15 Aug 2019
Viewed by 512
Abstract
The measurement of the photocatalytic activity of building materials is quite time-consuming. Up until now, researchers have mainly used the equipment described in ISO 22197-1 to ISO 22197-4 for the determination of air purification activity, although other apparatus such as colorimeters, UV-Vis/DR spectroscopes [...] Read more.
The measurement of the photocatalytic activity of building materials is quite time-consuming. Up until now, researchers have mainly used the equipment described in ISO 22197-1 to ISO 22197-4 for the determination of air purification activity, although other apparatus such as colorimeters, UV-Vis/DR spectroscopes and equipment for contact angle measurements have also been used. Usually, photocatalytic activity measurements take from one hour up to several hours. In this study, we present a very fast method for the measurement of the photocatalytic activity of gypsum. A specially designed printer with a modified bubblejet cartridge was used to apply a special ink on the surface of gypsum plates. Then the surface was irradiated by UV-A light and every 3 s a picture of the surface was taken. The results showed that the discoloration of the dye occurs after a few seconds of irradiation and the time depends on the amount of photocatalyst used as well as the number of printed ink layers. It was concluded that it is possible to use this method for a quick comparison of the photocatalytic activity of different types of modified gypsum materials. Full article
(This article belongs to the Special Issue Environmental Applications of Photocatalytic Processes)
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Open AccessArticle
Core-Shell Fe3O4@NCS-Mn Derived from Chitosan-Schiff Based Mn Complex with Enhanced Catalytic Activity for Oxygen Reduction Reaction
Catalysts 2019, 9(8), 692; https://doi.org/10.3390/catal9080692 - 15 Aug 2019
Viewed by 463
Abstract
A core-shell type of Fe3O4/NCS-Mn composite was prepared by pyrolyzing a precursor fabricated by coating a chitosan-Schiff base Mn complex on Fe3O4 cores. For comparison purposes, the Fe3O4@NCS sample in the absence [...] Read more.
A core-shell type of Fe3O4/NCS-Mn composite was prepared by pyrolyzing a precursor fabricated by coating a chitosan-Schiff base Mn complex on Fe3O4 cores. For comparison purposes, the Fe3O4@NCS sample in the absence of Mn and the Fe3O4@NC sample derived from just chitosan coating Fe3O4 were also prepared. Among the three catalysts, Fe3O4@NCS-Mn demonstrates the best electrocatalytic activity compared to commercial Pt/C (20%) for oxygen reduction reaction (ORR). The average of the transferred electron number (n) approached 3.6 in the range of −0.3 to −0.8 V (vs. Ag/AgCl). Moreover, the catalyst exhibited high stability and durability against methanol and may potentially be a promising ORR catalyst for fuel cells. Full article
(This article belongs to the Section Electrocatalysis)
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Open AccessReview
Cerium- and Iron-Oxide-Based Nanozymes in Tissue Engineering and Regenerative Medicine
Catalysts 2019, 9(8), 691; https://doi.org/10.3390/catal9080691 - 15 Aug 2019
Viewed by 552
Abstract
Nanoparticulate materials displaying enzyme-like properties, so-called nanozymes, are explored as substitutes for natural enzymes in several industrial, energy-related, and biomedical applications. Outstanding high stability, enhanced catalytic activities, low cost, and availability at industrial scale are some of the fascinating features of nanozymes. Furthermore, [...] Read more.
Nanoparticulate materials displaying enzyme-like properties, so-called nanozymes, are explored as substitutes for natural enzymes in several industrial, energy-related, and biomedical applications. Outstanding high stability, enhanced catalytic activities, low cost, and availability at industrial scale are some of the fascinating features of nanozymes. Furthermore, nanozymes can also be equipped with the unique attributes of nanomaterials such as magnetic or optical properties. Due to the impressive development of nanozymes during the last decade, their potential in the context of tissue engineering and regenerative medicine also started to be explored. To highlight the progress, in this review, we discuss the two most representative nanozymes, namely, cerium- and iron-oxide nanomaterials, since they are the most widely studied. Special focus is placed on their applications ranging from cardioprotection to therapeutic angiogenesis, bone tissue engineering, and wound healing. Finally, current challenges and future directions are 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
Alternative Raw Materials to Produce Biodiesel through Alkaline Heterogeneous Catalysis
Catalysts 2019, 9(8), 690; https://doi.org/10.3390/catal9080690 - 15 Aug 2019
Viewed by 461
Abstract
Recent research focuses on new biodiesel production and purification technologies that seek a carbon-neutral footprint, as well as cheap, renewable and abundant raw materials that do not compete with the demand for food. Then, many attractive alternatives arise due to their availability or [...] Read more.
Recent research focuses on new biodiesel production and purification technologies that seek a carbon-neutral footprint, as well as cheap, renewable and abundant raw materials that do not compete with the demand for food. Then, many attractive alternatives arise due to their availability or low-cost, such as used cooking oil, Jatropha oil (non-edible) or byproducts of vegetable oil refineries. Due to their composition and the presence of moisture, these oils may need a pretreatment to reach the established conditions to be used in the biodiesel production process so that the final product complies with the international quality standards. In this work, a solid catalyst based on 10 wt % sodium oxide supported on mesoporous silica SBA-15, was employed in the transesterification of different feedstocks (commercial sunflower and soybean oil, used cooking oil, acid oil from soapstock and Jatropha hieronymi oil) with absolute methanol in the following reaction conditions—2–8 wt % catalyst, 14:1 methanol to oil molar ratio, 60 °C, vigorous magnetic stirring and 5 h of reaction. In this way, first- and second-generation biodiesel was obtained through heterogeneous catalysis with methyl ester yields between 52 and 97 wt %, depending on the free fatty acid content and the moisture content of the oils. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis in Biodiesel Production)
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Open AccessArticle
The Effects of Catalyst Support and Temperature on the Hydrotreating of Waste Cooking Oil (WCO) over CoMo Sulfided Catalysts
Catalysts 2019, 9(8), 689; https://doi.org/10.3390/catal9080689 - 15 Aug 2019
Viewed by 497
Abstract
Waste cooking oil (WCO) hydrotreating to produce green diesel is good for both the environmental protection and energy recovery problems. The roles of catalyst support and reaction temperature on reactions during WCO hydrotreating process were evaluated over an unsupported and a commercial sulfided [...] Read more.
Waste cooking oil (WCO) hydrotreating to produce green diesel is good for both the environmental protection and energy recovery problems. The roles of catalyst support and reaction temperature on reactions during WCO hydrotreating process were evaluated over an unsupported and a commercial sulfided cobalt and molybdenum (CoMoS) catalyst supported by a mixture of Al2O3, TiO2, and SiO2. The presence of catalyst support helped to improve the dispersion and enlarge the surface area of CoMoS, and was found to be a key factor in reducing reaction temperature, in enhancing the hydrodeoxygenation (HDO) and hydrogenation capabilities, and in decreasing polymerization capability. The increase of reaction temperature strongly improved the deoxygenation, hydrogenation, and cracking reaction activities. Compared to the unsupported CoMoS, the supported one exhibited good deoxygenation and hydrogenation capabilities at 340 °C in WCO hydrotreating to produce diesel fraction; however, high temperature operation needs to be carefully controlled because it may cause overcracking and dehydrogenation. Full article
(This article belongs to the Special Issue Catalysis for the Production of Sustainable Fuels and Chemicals)
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Open AccessArticle
Ni/CeO2 Structured Catalysts for Solar Reforming of Spent Solvents
Catalysts 2019, 9(8), 688; https://doi.org/10.3390/catal9080688 - 15 Aug 2019
Viewed by 546
Abstract
Spent solvents of the packaging industry are disposed of, thus representing economic, safety, and environmental issues. Steam reforming of these solvent streams can be an alternative, allowing their valorization to syngas. In this work, ceria supported nickel catalysts were deposed onto silicon carbide [...] Read more.
Spent solvents of the packaging industry are disposed of, thus representing economic, safety, and environmental issues. Steam reforming of these solvent streams can be an alternative, allowing their valorization to syngas. In this work, ceria supported nickel catalysts were deposed onto silicon carbide (SiC) honeycomb monoliths; these structured catalysts can be potentially used in solar steam reforming. Catalysts were characterized by SEM/EDS and tested in a lab-scale rig under conventional heating. Two spent solvent streams, coming from the distillation plant of the packaging industry Icimendue, were used as fuels. Catalytic tests have been carried out by changing the steam/carbon ratio, oxygen/carbon ratio, operating pressure, and fuel. The effect of the Ni content and the type of ceria were also studied. The best performances were obtained at low Ni content and by using micrometric rather than nanometric ceria as support. The structured catalysts showed good coking resistance, especially at H2O/C > 2, with oxygen addition furnishing a marginal improvement. On the contrary, oxygen feeding reduced the gas yield due to the formation of by-products being less reactive in reforming reactions. Performing the reforming process at high pressure the gas yield increased due to faster kinetics (higher reactants concentrations), higher contact times (slower flow rates), and process intensification. These results suggest that the proposed structured catalysts could be successfully applied in the solar reforming of spent solvents. Full article
(This article belongs to the Special Issue Catalytic Applications of CeO2-Based Materials)
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Open AccessFeature PaperArticle
Clicking Azides and Alkynes with Poly(pyrazolyl)borate-Copper(I) Catalysts: An Experimental and Computational Study
Catalysts 2019, 9(8), 687; https://doi.org/10.3390/catal9080687 - 14 Aug 2019
Viewed by 531
Abstract
The synthesis of 1,4-disubstituted-1,2,3-triazoles under a copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) regime was accomplished in high yields and a regioselective manner by using two homoscorpionate poly(pyrazolyl)borate anions: tris(pyrazolyl)hydroborate (HB(pz)3) and bis(pyrazolyl)hydroborate (H2B(pz)2), which stabilized in situ [...] Read more.
The synthesis of 1,4-disubstituted-1,2,3-triazoles under a copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) regime was accomplished in high yields and a regioselective manner by using two homoscorpionate poly(pyrazolyl)borate anions: tris(pyrazolyl)hydroborate (HB(pz)3) and bis(pyrazolyl)hydroborate (H2B(pz)2), which stabilized in situ the catalytically active copper (I) center. The [3+2] cycloaddition (32CA) reactions took place under strict click conditions, including room temperature and a mixture of environmentally benign solvents such as water/ethanol in a 1:1 (v/v) ratio. These click chemistry conditions were applied to form complex 1,2,3-triazoles-containing sugar moieties, which are potentially relevant from a biological point of view. Computational modeling carried out by DFT methodologies at the B3LYP/6-31G(d) level showed that the coordination of poly(pyrazolyl)borate-copper(I) to alkyne groups produced relevant changes in terms of generating a high polar copper(I)-acetylide intermediates. The analysis of the global and local reactivity indices explains correctly the role of poly(pyrazolyl)borate ligands in the stabilization and activation of the copper(I) catalyst in the studied 32CA reactions. Full article
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Open AccessArticle
Effect of Chlorine-Containing VOCs on Silver Migration and Sintering in ZSM-5 Used in a TSA Process
Catalysts 2019, 9(8), 686; https://doi.org/10.3390/catal9080686 - 14 Aug 2019
Cited by 1 | Viewed by 484
Abstract
Silver nanoparticles are currently one of the most studied nanostructured nanomaterials. Because nanoparticle size and dispersion act together in determining a material’s physical and chemical properties, there is a continuous quest to develop size-controlled synthesis methods. Nonetheless, the instability of the nanometer-sized particles, [...] Read more.
Silver nanoparticles are currently one of the most studied nanostructured nanomaterials. Because nanoparticle size and dispersion act together in determining a material’s physical and chemical properties, there is a continuous quest to develop size-controlled synthesis methods. Nonetheless, the instability of the nanometer-sized particles, which is caused by their tendency to aggregate irreversibly into larger particles, remains a recurrent problem. The use of confining scaffolds, such as the regular system of cages in a crystalline zeolite-type material, is often reported in the literature as an efficient solution to overcome particle migration at the surface. Silver nanoparticles encapsulated in ZSM-5 ([email protected]) represent a new generation of adsorbent for Xe enrichment from the atmosphere that is currently being developed at the pilot scale in a Temperature Swing Adsorption (TSA) process. In this study, we have found that the presence of Cl-containing compounds in the air (VOCs) leads to a poisoning of the active silver phase by the formation of silver chloride. By a careful study of process parameters, we have found that most of the chlorine can be removed by heat treatment above 573 K so that the adsorption properties of silver are regenerated. That said, when applying 573 K temperature regeneration at the pilot scale, we observe a very minor but observable decay of xenon adsorption capacity that continues cycle after cycle. The mechanism of capacity decay is discussed in terms of (i) the residual presence of Cl at the surface of silver nanoparticles, (ii) the aggregation of silver nanoparticles into larger particles (sintering mechanism), and (iii) the acceleration of silver particle migration to the surface and sintering. Full article
(This article belongs to the Special Issue Synthesis and Application of Zeolite Catalysts)
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Open AccessArticle
Effect of Transition Metal Additives on the Catalytic Performance of Cu–Mn/SAPO-34 for Selective Catalytic Reduction of NO with NH3 at Low Temperature
Catalysts 2019, 9(8), 685; https://doi.org/10.3390/catal9080685 - 13 Aug 2019
Viewed by 422
Abstract
The adsorption of NO, NH3, H2O, and SO2 gaseous molecules on different transition metal oxides was studied based on density function theory (DFT), and three better-performing transition metal elements (Fe, Co, and Ce) were selected. Cu–Mn/SAPO-34 catalysts were [...] Read more.
The adsorption of NO, NH3, H2O, and SO2 gaseous molecules on different transition metal oxides was studied based on density function theory (DFT), and three better-performing transition metal elements (Fe, Co, and Ce) were selected. Cu–Mn/SAPO-34 catalysts were prepared by impregnation method and then modified by the selected transition metals (Fe, Co, and Ce); the SO2 resistance experiments and characterizations including Brunner−Emmet−Teller (BET), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), and thermal gravity analysis (TG)-differential thermal gravity (DTG) before and after SO2 poisoning were conducted. The results showed that the deactivation of the Cu–Mn/SAPO-34 catalyst is ascribed to the deposition of lots of ammonium sulfates on the surface, depositing on the active sites and inhibiting the adsorption of NH3. After the modification of Fe, Co, and Ce oxides, the SO2 resistance of the modified Cu–Mn/SAPO-34 catalyst was significantly enhanced due to the less formation of ammonium sulfates. Among all these modified Cu–Mn/SAPO-34 catalysts, the Cu–Mn–Ce/SAPO-34 exhibited the highest SO2 resistance owing to the decreased decomposition temperature and the trapper of ceria for capturing SO2 to form Ce(SO4)2, further inhibiting the deposition of ammonium sulfates. Full article
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Open AccessArticle
Improved Hydrothermal Stability in Glass Diesel Soot Oxidation Catalysts
Catalysts 2019, 9(8), 684; https://doi.org/10.3390/catal9080684 - 13 Aug 2019
Viewed by 486
Abstract
The hydrothermal stability of K-Ca-Si-O glass soot oxidation catalysts has been improved by substitution of Ce and Zr for Ca. This work demonstrates that glasses can be tailored to withstand the challenging diesel exhaust hydrothermal environment by considering the field strengths and partial [...] Read more.
The hydrothermal stability of K-Ca-Si-O glass soot oxidation catalysts has been improved by substitution of Ce and Zr for Ca. This work demonstrates that glasses can be tailored to withstand the challenging diesel exhaust hydrothermal environment by considering the field strengths and partial molar free energies of the hydration reactions (ΔGi) of the cation species in the glass. The result is a glass that shows less formation of precipitates after 2 h hydrothermal exposure in air with 7% H2O at temperatures ranging from 300–700 °C. A K-Ca-Si-O glass with a soot T50 (the temperature when 50% of the soot is oxidized) of 394 °C was found to degrade to 468 °C after a 2 h, 700 °C hydrothermal exposure, whereas the improved K-Ce-Zr-Si-O glass only changed from 407 °C to 427 °C after the same treatment. Full article
(This article belongs to the Section Catalytic Materials)
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Open AccessArticle
Performance Analysis of Biocathode in Bioelectrochemical CO2 Reduction
Catalysts 2019, 9(8), 683; https://doi.org/10.3390/catal9080683 - 12 Aug 2019
Viewed by 525
Abstract
Microbial electrosynthesis (MES) biogas upgrading is done via reduction of carbon dioxide to methane through electroactive microbial catalysis. The baseline MES mode of operation showed about a 39% increase in the methane production rate compared to the open circuit mode of operation. MES [...] Read more.
Microbial electrosynthesis (MES) biogas upgrading is done via reduction of carbon dioxide to methane through electroactive microbial catalysis. The baseline MES mode of operation showed about a 39% increase in the methane production rate compared to the open circuit mode of operation. MES is capable of producing acetic acid at relatively more negative potential (−0.80 to –0.90 V vs. Standard Hydrogen Electrode (SHE)) than the potential at which it produces methane (−0.65 V vs. SHE). The optimum pH for enhancing the electroactive acetogens is found to be around 6.8–7.0 while a pH of around 7.0–7.5 enhances the electroactive methanogens performance. The biocathode adaptation test reveals that 45% of the methane was produced through the electrochemical pathway with a coulombic efficiency of 100% while maintaining heterotrophic efficiency above 99%. Full article
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Open AccessArticle
Insights into the Pyrolysis Processes of Ce-MOFs for Preparing Highly Active Catalysts of Toluene Combustion
Catalysts 2019, 9(8), 682; https://doi.org/10.3390/catal9080682 - 10 Aug 2019
Viewed by 501
Abstract
Metal organic frameworks (MOFs) have recently been used as precursors of the catalysts for the combustion of volatile organic compounds (VOCs). In the present work, three kinds of CeO2 catalysts were successfully synthesized from Ce-MOF-808, Ce-BTC, and Ce-UiO-66, with specific topological structures [...] Read more.
Metal organic frameworks (MOFs) have recently been used as precursors of the catalysts for the combustion of volatile organic compounds (VOCs). In the present work, three kinds of CeO2 catalysts were successfully synthesized from Ce-MOF-808, Ce-BTC, and Ce-UiO-66, with specific topological structures and coordinate environments. Catalysts with small particle size, stacking mode, and structural defects could be created by pyrolysis of Ce-MOFs, which affects the activity in the toluene combustion significantly. Raman spectra, XPS, and OSC studies were performed to reveal the formation of defect sites. The thermal redox properties were determined by H2-TPR. Catalytic activity tests were conducted on the toluene combustion, and CeO2-MOF-808 showed the best catalytic performance (T90 = 278 °C) due to its having the largest specific surface area, abundant active surface oxygen species, and low-temperature reducibility. Full article
(This article belongs to the Special Issue Catalytic Applications of CeO2-Based Materials)
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Open AccessFeature PaperArticle
Improvement of Photocatalytic H2-Generation under Visible Light Irradiation by Controlling the Band Gap of ZnIn2S4 with Cu and In
Catalysts 2019, 9(8), 681; https://doi.org/10.3390/catal9080681 - 10 Aug 2019
Viewed by 430
Abstract
The band gap controlled photocatalyst (Zn0.74Cu0.13In2S3.805) was prepared via a simple one-step solvothermal method. The effects of doping of Cu+ and excess In on the photocatalytic activity of ZnIn2S4 photocatalyst were [...] Read more.
The band gap controlled photocatalyst (Zn0.74Cu0.13In2S3.805) was prepared via a simple one-step solvothermal method. The effects of doping of Cu+ and excess In on the photocatalytic activity of ZnIn2S4 photocatalyst were investigated. In addition, optical properties, surface morphology and crystal structure were evaluated. The maximum H2 evolution rate (2370 µmol h−1 g−1) was achieved with Zn0.74Cu0.13In2S3.805, which was about five times higher than that of untreated ZnIn2S4 under visible light (λ ≥ 420 nm). The band gap of Zn0.74Cu0.13In2S3.805 decreased to 1.98 eV by raising the maximum position of the valence band, compared to ZnIn2S4. Furthermore, the recombination of electron hole pairs was effectively reduced. This research contributes to the development of highly active photocatalysts under visible light. Full article
(This article belongs to the Special Issue State-of-the-Art Photocatalytical Technology in Asia)
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Open AccessFeature PaperReview
Insights into the TiO2-Based Photocatalytic Systems and Their Mechanisms
Catalysts 2019, 9(8), 680; https://doi.org/10.3390/catal9080680 - 09 Aug 2019
Viewed by 628
Abstract
Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H2 production, CO2 reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO [...] Read more.
Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H2 production, CO2 reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO2 is blooming in the field of photocatalysis, which is largely explored for various photocatalytic applications. The deeper understanding of TiO2 photocatalysis has led to the design of new photocatalytic materials with multiple functionalities. Accordingly, this paper exclusively reviews the recent developments in the modification of TiO2 photocatalyst towards the understanding of its photocatalytic mechanisms. These modifications generally involve the physical and chemical changes in TiO2 such as anisotropic structuring and integration with other metal oxides, plasmonic materials, carbon-based materials, etc. Such modifications essentially lead to the changes in the energy structure of TiO2 that largely boosts up the photocatalytic process via enhancing the band structure alignments, visible light absorption, carrier separation, and transportation in the system. For instance, the ability to align the band structure in TiO2 makes it suitable for multiple photocatalytic processes such as degradation of various pollutants, H2 production, CO2 conversion, etc. For these reasons, TiO2 can be realized as a prototypical photocatalyst, which paves ways to develop new photocatalytic materials in the field. In this context, this review paper sheds light into the emerging trends in TiO2 in terms of its modifications towards multifunctional photocatalytic applications. Full article
(This article belongs to the Special Issue Emerging Trends in TiO2 Photocatalysis and Applications)
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Open AccessFeature PaperArticle
In Silico Acetylene [2+2+2] Cycloadditions Catalyzed by Rh/Cr Indenyl Fragments
Catalysts 2019, 9(8), 679; https://doi.org/10.3390/catal9080679 - 09 Aug 2019
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Abstract
Metal-catalyzed alkyne [2+2+2] cycloadditions provide a variety of substantial aromatic compounds of interest in the chemical and pharmaceutical industries. Herein, the mechanistic aspects of the acetylene [2+2+2] cycloaddition mediated by bimetallic half-sandwich catalysts [Cr(CO)3IndRh] (Ind = (C9H7) [...] Read more.
Metal-catalyzed alkyne [2+2+2] cycloadditions provide a variety of substantial aromatic compounds of interest in the chemical and pharmaceutical industries. Herein, the mechanistic aspects of the acetylene [2+2+2] cycloaddition mediated by bimetallic half-sandwich catalysts [Cr(CO)3IndRh] (Ind = (C9H7), indenyl anion) are investigated. A detailed exploration of the potential energy surfaces (PESs) was carried out to identify the intermediates and transition states, using a relativistic density functional theory (DFT) approach. For comparison, monometallic parent systems, i.e., CpRh (Cp = (C5H5), cyclopentadienyl anion) and IndRh, were included in the analysis. The active center is the rhodium nucleus, where the [2+2+2] cycloaddition occurs. The coordination of the Cr(CO)3 group, which may be in syn or anti conformation, affects the energetics of the catalytic cycle as well as the mechanism. The reaction and activation energies and the turnover frequency (TOF) of the catalytic cycles are rationalized, and, in agreement with the experimental findings, our computational analysis reveals that the presence of the second metal favors the catalysis. Full article
(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)
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Open AccessArticle
Laboratory and On-Road Evaluation of a GPF-Equipped Gasoline Vehicle
Catalysts 2019, 9(8), 678; https://doi.org/10.3390/catal9080678 - 09 Aug 2019
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Abstract
The introduction of a solid particle number limit for vehicles with gasoline direct injection (GDI) engines resulted in a lot of research and improvements in this field in the last decade. The requirement to also fulfil the limit in the recently introduced real-driving [...] Read more.
The introduction of a solid particle number limit for vehicles with gasoline direct injection (GDI) engines resulted in a lot of research and improvements in this field in the last decade. The requirement to also fulfil the limit in the recently introduced real-driving emissions (RDE) regulation led to the introduction of gasoline particulate filters (GPFs) in European vehicle models. As the pre-standardisation research was based on engines, retrofitted vehicles and prototype vehicles, there is a need to better characterise the actual emissions of GPF-equipped GDI vehicles. In the present study we investigate one of the first mass production vehicles with GPF available in the European market. Regulated and non-regulated pollutants were measured over different test cycles and ambient temperatures (23 °C and −7 °C) in the laboratory and different on-road routes driven normally or dynamically and up to 1100 m altitude. The results showed that the vehicle respected all applicable limits. However, under certain conditions high emissions of some pollutants were measured (total hydrocarbons emissions at −7 °C, high CO during dynamic RDE tests and high NOx emissions in one dynamic RDE test). The particle number emissions, even including those below 23 nm, were lower than 6 × 1010 particles/km under all laboratory test cycles and on-road routes, which are <10% of the current laboratory limit (6 × 1011 particles/km). Full article
(This article belongs to the Special Issue Catalytic Gasoline Particulate Filters)
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Open AccessArticle
High Performance of Mn-Doped MgAlOx Mixed Oxides for Low Temperature NOx Storage and Release
Catalysts 2019, 9(8), 677; https://doi.org/10.3390/catal9080677 - 09 Aug 2019
Viewed by 447
Abstract
NOx storage-reduction (NSR) is a potential approach for the effective removal of NOx under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlOx) with high performance for low temperature NOx storage and release were derived from [...] Read more.
NOx storage-reduction (NSR) is a potential approach for the effective removal of NOx under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlOx) with high performance for low temperature NOx storage and release were derived from hydrotalcites precursors prepared by a facile coprecipitation method. The catalysts were characterized by X-ray diffraction (XRD), SEM, N2 adsorption-desorption, H2-TPR, FT-IR, and X-ray photoelectron spectroscopy (XPS) techniques. The Mn-doped MgAlOx catalysts exhibited high NOx storage capacity (NSC) at low temperature range (150–300 °C), which was related to their increased surface area, improved reducibility and higher surface Mn3+ content. The largest NSC measured, 426 μmol/g, was observed for NOx adsorption at 200 °C on Mn15 catalyst (the sample containing 15 wt% of Mn). The in situ DRIFTS spectra of NOx adsorption proved that the Mn-doped hydrotalcite catalysts are preferred for low temperature NOx storage and release due to their ability to store NOx mainly in the form of thermally labile nitrites. NSR cycling tests revealed the NOx removal rate of Mn15 sample can reach above 70% within the wide temperature range of 150–250 °C. Besides, the influence of CO2, soot, H2O and SO2 on NOx storage performance of Mn15 catalyst was also studied. In all, owning to their excellent NOx storage capacity, NSR cycling performance, and resistance to CO2, soot, SO2 and H2O, the Mn-doped MgAlOx NSR catalysts have broad application prospects in NOx control at low temperatures. Full article
(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)
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Open AccessFeature PaperArticle
The Relationship between Reaction Temperature and Carbon Deposition on Nickel Catalysts Based on Al2O3, ZrO2 or SiO2 Supports during the Biogas Dry Reforming Reaction
Catalysts 2019, 9(8), 676; https://doi.org/10.3390/catal9080676 - 09 Aug 2019
Viewed by 453
Abstract
The tackling of carbon deposition during the dry reforming of biogas (BDR) necessitates research of the surface of spent catalysts in an effort to obtain a better understanding of the effect that different carbon allotropes have on the deactivation mechanism and correlation of [...] Read more.
The tackling of carbon deposition during the dry reforming of biogas (BDR) necessitates research of the surface of spent catalysts in an effort to obtain a better understanding of the effect that different carbon allotropes have on the deactivation mechanism and correlation of their formation with catalytic properties. The work presented herein provides a comparative assessment of catalytic stability in relation to carbon deposition and metal particle sintering on un-promoted Ni/Al2O3, Ni/ZrO2 and Ni/SiO2 catalysts for different reaction temperatures. The spent catalysts were examined using thermogravimetric analysis (TGA), Raman spectroscopy, high angle annular dark field scanning transmission electron microscopy (STEM-HAADF) and X-ray photoelectron spectroscopy (XPS). The results show that the formation and nature of carbonaceous deposits on catalytic surfaces (and thus catalytic stability) depend on the interplay of a number of crucial parameters such as metal support interaction, acidity/basicity characteristics, O2– lability and active phase particle size. When a catalytic system possesses only some of these beneficial characteristics, then competition with adverse effects may overshadow any potential benefits. Full article
(This article belongs to the Special Issue Catalyst Deactivation in Hydrocarbon Processing)
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Open AccessArticle
Gel-Type and Macroporous Cross-Linked Copolymers Functionalized with Acid Groups for the Hydrolysis of Wheat Straw Pretreated with an Ionic Liquid
Catalysts 2019, 9(8), 675; https://doi.org/10.3390/catal9080675 - 08 Aug 2019
Viewed by 375
Abstract
Several sulfonated cross-linked copolymers functionalized with hydroxyl and carboxylic groups have been synthesized. The amount of the cross-linking monomer was tailored (from 4% up to 40%) to tune the resulting micro- and nano-morphologies, and two types of catalysts, namely, gel-type and macroreticular catalysts, [...] Read more.
Several sulfonated cross-linked copolymers functionalized with hydroxyl and carboxylic groups have been synthesized. The amount of the cross-linking monomer was tailored (from 4% up to 40%) to tune the resulting micro- and nano-morphologies, and two types of catalysts, namely, gel-type and macroreticular catalysts, were obtained. These copolymers were employed in the catalytic hydrolysis of wheat straw pretreated in 1-ethyl-3-methylimidazolium acetate to obtain sugars. Remarkably, the presence of additional oxygenated groups enhances the catalytic performances of the polymers by favoring the adsorption of β-(1,4)-glucans and makes these materials significantly more active than an acidic resin bearing only sulfonic groups (i.e., Amberlyst 70). In addition, the structure of the catalyst (gel-type or macroreticular) appears to be a determining factor in the catalytic process. The gel-type structure provides higher glucose concentrations because the morphology in the swollen state is more favorable in terms of the accessibility of the catalytic centers. The observed catalytic behavior suggests that the substrate diffuses within the swollen polymer matrix and indirectly confirms that the pretreatment based on dissolution/precipitation in ionic liquids yields a substantial enhancement of the conversion of lignocellulosic biomass to glucose in the presence of heterogeneous catalysts. Full article
(This article belongs to the Special Issue Catalytic Biomass to Renewable Biofuels and Biomaterials)
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Open AccessEditorial
Catalytic Processes for The Valorization of Biomass Derived Molecules
Catalysts 2019, 9(8), 674; https://doi.org/10.3390/catal9080674 - 08 Aug 2019
Viewed by 426
Abstract
Industrial chemistry is changing its fossil distinctiveness into a new green identity by using renewable resources [...] Full article
(This article belongs to the Special Issue Catalytic Processes for The Valorisation of Biomass Derived Molecules)
Open AccessArticle
Two-Step Production of Neofructo-Oligosaccharides Using Immobilized Heterologous Aspergillus terreus 1F-Fructosyltransferase Expressed in Kluyveromyces lactis and Native Xanthophyllomyces dendrorhous G6-Fructosyltransferase
Catalysts 2019, 9(8), 673; https://doi.org/10.3390/catal9080673 - 07 Aug 2019
Viewed by 415
Abstract
Fructo-oligosaccharides (FOS) are prebiotic low-calorie sweeteners that are synthesized by the transfer of fructose units from sucrose by enzymes known as fructosyltransferases. If these enzymes generate β-(2,6) glycosidic bonds, the resulting oligosaccharides belong to the neoseries (neoFOS). Here, we characterized the properties of [...] Read more.
Fructo-oligosaccharides (FOS) are prebiotic low-calorie sweeteners that are synthesized by the transfer of fructose units from sucrose by enzymes known as fructosyltransferases. If these enzymes generate β-(2,6) glycosidic bonds, the resulting oligosaccharides belong to the neoseries (neoFOS). Here, we characterized the properties of three different fructosyltransferases using a design of experiments approach based on response surface methodology with a D-optimal design. The reaction time, pH, temperature, and substrate concentration were used as parameters to predict three responses: The total enzyme activity, the concentration of neoFOS and the neoFOS yield relative to the initial concentration of sucrose. We also conducted immobilization studies to establish a cascade reaction for neoFOS production with two different fructosyltransferases, achieving a total FOS yield of 47.02 ± 3.02%. The resulting FOS mixture included 53.07 ± 1.66 mM neonystose (neo-GF3) and 20.8 ± 1.91 mM neo-GF4. Full article
(This article belongs to the Special Issue Immobilization of Enzymes)
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Open AccessCommunication
Synthesis of Hierarchical Titanium Silicalite-1 Using a Carbon-Silica-Titania Composite from Xerogel Mild Carbonization
Catalysts 2019, 9(8), 672; https://doi.org/10.3390/catal9080672 - 07 Aug 2019
Viewed by 404
Abstract
Hierarchical titanium silicalite-1 (HTS-1) zeolites are an important class of catalytic materials due to their enhanced mass transfer and improved catalytic performance. In this study, HTS-1 zeolites have been successfully prepared by the hydrothermal crystallization of carbon-silica-titania (CST) composites. Compared with the direct [...] Read more.
Hierarchical titanium silicalite-1 (HTS-1) zeolites are an important class of catalytic materials due to their enhanced mass transfer and improved catalytic performance. In this study, HTS-1 zeolites have been successfully prepared by the hydrothermal crystallization of carbon-silica-titania (CST) composites. Compared with the direct carbonization method, the mild carbonization of SiO2-TiO2/Tween 40 xerogel in the presence of sulfuric acid can effectively improve both the content and mesoporous structure of carbon material in the CST composites, which enables carbon materials to better play the role of a mesoporous template during the crystallization process. The resultant zeolite has both ordered micropores and interconnected mesopores and macropores, which are similar to the skeleton of the carbon template trapped in the TS–1 crystals. Moreover, the HTS–1 zeolite displays outstanding catalytic performance in oxidative desulfurization of bulky sulfur compounds. Full article
(This article belongs to the Special Issue Synthesis and Application of Zeolite Catalysts)
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Open AccessReview
Microbial Phosphotriesterase: Structure, Function, and Biotechnological Applications
Catalysts 2019, 9(8), 671; https://doi.org/10.3390/catal9080671 - 07 Aug 2019
Viewed by 474
Abstract
The role of phosphotriesterase as an enzyme which is able to hydrolyze organophosphate compounds cannot be disputed. Contamination by organophosphate (OP) compounds in the environment is alarming, and even more worrying is the toxicity of this compound, which affects the nervous system. Thus, [...] Read more.
The role of phosphotriesterase as an enzyme which is able to hydrolyze organophosphate compounds cannot be disputed. Contamination by organophosphate (OP) compounds in the environment is alarming, and even more worrying is the toxicity of this compound, which affects the nervous system. Thus, it is important to find a safer way to detoxify, detect and recuperate from the toxicity effects of this compound. Phosphotriesterases (PTEs) are mostly isolated from soil bacteria and are classified as metalloenzymes or metal-dependent enzymes that contain bimetals at the active site. There are three separate pockets to accommodate the substrate into the active site of each PTE. This enzyme generally shows a high catalytic activity towards phosphotriesters. These microbial enzymes are robust and easy to manipulate. Currently, PTEs are widely studied for the detection, detoxification, and enzyme therapies for OP compound poisoning incidents. The discovery and understanding of PTEs would pave ways for greener approaches in biotechnological applications and to solve environmental issues relating to OP contamination. Full article
(This article belongs to the Special Issue Biocatalytic Applications in Biotechnology)
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Open AccessArticle
Catalytic Dehydration of Ethanol over WOx Nanoparticles Supported on MFI (Mobile Five) Zeolite Nanosheets
Catalysts 2019, 9(8), 670; https://doi.org/10.3390/catal9080670 - 06 Aug 2019
Viewed by 496
Abstract
Ethylene can be synthesized in a renewable manner by dehydrating bioethanol over supported metal oxide nanoparticle catalysts. Here, a series of nanoparticulate tungsten oxides supported on MFI (Mobil five) zeolite nanosheets was prepared at different W loadings (1 to 6 mol %) using [...] Read more.
Ethylene can be synthesized in a renewable manner by dehydrating bioethanol over supported metal oxide nanoparticle catalysts. Here, a series of nanoparticulate tungsten oxides supported on MFI (Mobil five) zeolite nanosheets was prepared at different W loadings (1 to 6 mol %) using the incipient wetness method and investigated with respect to the ability to catalyze the dehydration of ethanol. The resulting samples were characterized by X-ray diffraction, electron microscopy, N2 isotherms, X-ray absorption fine structures, and by the temperature-programmed desorption of NH3. The results obtained showed that WOx nanoparticles were homogeneously distributed over the entire void space of nanosheet samples up to a loading of 2 mol %, after which large WOx nanoparticles with needle-like morphology were formed on the surface of the zeolite nanosheet beyond 2mol%. The number of acid sites increased with WOx loading and, as a result, EtOH conversion progressively increased with WOx loading up to 6 mol %. At reaction temperatures of >390 °C, homogeneously distributed WOx nanoparticles showed slightly higher ethylene selectivity than nano-needle structured WOx. However, nano-needle structured WOx exhibited greater catalytic stability. In terms of ethylene yield over 8 h, needle-like WOx nanoparticles were found to be more suitable for the acid-catalyzed dehydration of ethanol than small-sized WOx nanoparticles. Full article
(This article belongs to the Special Issue Synthesis and Application of Zeolite Catalysts)
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Open AccessArticle
In situ Decolorization Monitoring of Textile Dyes for an Optimized UV-LED/TiO2 Reactor
Catalysts 2019, 9(8), 669; https://doi.org/10.3390/catal9080669 - 06 Aug 2019
Viewed by 430
Abstract
Heterogeneous photocatalysis, using photocatalysts in suspension to eliminate diverse contaminants, including textile wastewater, has several advantages. Nevertheless, current absorbance and decolorization measurements imply sample acquisition by extraction at a fixed rate with consequent photocatalyst removal. This study presents online monitoring for the decolorization [...] Read more.
Heterogeneous photocatalysis, using photocatalysts in suspension to eliminate diverse contaminants, including textile wastewater, has several advantages. Nevertheless, current absorbance and decolorization measurements imply sample acquisition by extraction at a fixed rate with consequent photocatalyst removal. This study presents online monitoring for the decolorization of six azo dyes, Orange PX-2R (OP2), Remazol Black B133 (RB), Procion Crimson H-EXL (PC), Procion Navy H-EXL (PN), Procion Blue H-EXL (PB), and Procion Yellow H-EXL (PY), analyzing the spectrum measured in situ by using the light scattering provided by the photocatalyst in suspension. The results obtained have corroborated the feasibility of obtaining absorbance and decolorization measurements, avoiding disturbances in the process due to a decrease in the volume in the reactor. Full article
(This article belongs to the Special Issue Environmental Applications of Photocatalytic Processes)
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