Catalysts

14 pages, 4360 KiB

Open AccessArticle

Photocatalytic Removal of Harmful Algae in Natural Waters by Ag/AgCl@ZIF-8 Coating under Sunlight

by Gongduan Fan, Zhong Chen, Bo Wang, Shimin Wu, Jing Luo, Xiaomei Zheng, Jiajun Zhan, Yifan You and Zhi Zhang

Catalysts 2019, 9(8), 698; https://doi.org/10.3390/catal9080698 - 20 Aug 2019

Cited by 16 | Viewed by 3959

Abstract

In order to control the cyanobacterial blooms in eutrophic water, an Ag/AgCl@ZIF-8 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/AgCl@ZIF-8 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/AgCl@ZIF-8 coating on algal removal and phytoplankton community structure in natural water samples with cyanobacterial blooms were investigated under sunlight. Results showed that Ag/AgCl@ZIF-8 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/AgCl@ZIF-8 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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16 pages, 4331 KiB

Open AccessArticle

Regarding the Nature of Charge Carriers Formed by UV or Visible Light Excitation of Carbon-Modified Titanium Dioxide

by Arsou Arimi, Carsten Günnemann, Mariano Curti and Detlef W. Bahnemann

Catalysts 2019, 9(8), 697; https://doi.org/10.3390/catal9080697 - 20 Aug 2019

Cited by 8 | Viewed by 5308

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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16 pages, 4081 KiB

Open AccessArticle

Optimization of the Washcoat Slurry for Hydrotalcite-Based LNT Catalyst

by Yue Zhu, Gang Lv, Chonglin Song, Bo Li, Yantao Zhu, Ye Liu, Wei Zhang and Yuanhong Wang

Catalysts 2019, 9(8), 696; https://doi.org/10.3390/catal9080696 - 20 Aug 2019

Cited by 1 | Viewed by 3651

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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16 pages, 5894 KiB

Open AccessArticle

Influence of MoS₂ on Activity and Stability of Carbon Nitride in Photocatalytic Hydrogen Production

by Ramesh P. Sivasankaran, Nils Rockstroh, Carsten R. Kreyenschulte, Stephan Bartling, Henrik Lund, Amitava Acharjya, Henrik Junge, Arne Thomas and Angelika Brückner

Catalysts 2019, 9(8), 695; https://doi.org/10.3390/catal9080695 - 17 Aug 2019

Cited by 14 | Viewed by 5310

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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15 pages, 2863 KiB

Open AccessArticle

Mild Preoxidation Treatment of Pt/TiO₂ Catalyst and Its Enhanced Low Temperature Formaldehyde Decomposition

by Kangzhong Shi, Lei Wang, Long Li, Xuejuan Zhao, Yuanyuan Chen, Zelin Hua, Xiaobao Li, Xiaoli Gu and Licheng Li

Catalysts 2019, 9(8), 694; https://doi.org/10.3390/catal9080694 - 16 Aug 2019

Cited by 18 | Viewed by 4113

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

(This article belongs to the Special Issue Recent Advances in Pt-Based Catalysts: Theoretical and Experimental Results)

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8 pages, 4287 KiB

Open AccessArticle

Fast Method for Testing the Photocatalytic Performance of Modified Gypsum

by Magdalena Janus, Kamila Zając, Clemens Ehm and Dietmar Stephan

Catalysts 2019, 9(8), 693; https://doi.org/10.3390/catal9080693 - 15 Aug 2019

Cited by 8 | Viewed by 5562

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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10 pages, 3559 KiB

Open AccessArticle

Core-Shell Fe₃O₄@NCS-Mn Derived from Chitosan-Schiff Based Mn Complex with Enhanced Catalytic Activity for Oxygen Reduction Reaction

by Jinhui Tong, Yuliang Li, Lili Bo, Wenhui Wang, Tao Li and Qi Zhang

Catalysts 2019, 9(8), 692; https://doi.org/10.3390/catal9080692 - 15 Aug 2019

Cited by 15 | Viewed by 4033

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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31 pages, 6274 KiB

Open AccessReview

Cerium- and Iron-Oxide-Based Nanozymes in Tissue Engineering and Regenerative Medicine

by Michelle M. T. Jansman and Leticia Hosta-Rigau

Catalysts 2019, 9(8), 691; https://doi.org/10.3390/catal9080691 - 15 Aug 2019

Cited by 22 | Viewed by 6721

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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14 pages, 1676 KiB

Open AccessArticle

Alternative Raw Materials to Produce Biodiesel through Alkaline Heterogeneous Catalysis

by Edgar M. Sánchez Faba, Gabriel O. Ferrero, Joana M. Dias and Griselda A. Eimer

Catalysts 2019, 9(8), 690; https://doi.org/10.3390/catal9080690 - 15 Aug 2019

Cited by 24 | Viewed by 4134

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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14 pages, 2256 KiB

Open AccessArticle

The Effects of Catalyst Support and Temperature on the Hydrotreating of Waste Cooking Oil (WCO) over CoMo Sulfided Catalysts

by Hui Wang, Kyle Rogers, Haiping Zhang, Guoliang Li, Jianglong Pu, Haoxuan Zheng, Hongfei Lin, Ying Zheng and Siauw Ng

Catalysts 2019, 9(8), 689; https://doi.org/10.3390/catal9080689 - 15 Aug 2019

Cited by 14 | Viewed by 5169

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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16 pages, 5651 KiB

Open AccessArticle

Ni/CeO₂ Structured Catalysts for Solar Reforming of Spent Solvents

by Gianluca Landi and Almerinda Di Benedetto

Catalysts 2019, 9(8), 688; https://doi.org/10.3390/catal9080688 - 15 Aug 2019

Cited by 3 | Viewed by 3132

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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17 pages, 4865 KiB

Open AccessFeature PaperArticle

Clicking Azides and Alkynes with Poly(pyrazolyl)borate-Copper(I) Catalysts: An Experimental and Computational Study

by Lahoucine Bahsis, Hicham Ben El Ayouchia, Hafid Anane, Carmen Ramirez de Arellano, Abdeslem Bentama, El Mestafa El Hadrami, Miguel Julve, Luis R. Domingo and Salah-Eddine Stiriba

Catalysts 2019, 9(8), 687; https://doi.org/10.3390/catal9080687 - 14 Aug 2019

Cited by 8 | Viewed by 3866

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

(This article belongs to the Special Issue Computational Chemistry and Catalysis: Prediction and Design)

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16 pages, 4050 KiB

Open AccessArticle

Effect of Chlorine-Containing VOCs on Silver Migration and Sintering in ZSM-5 Used in a TSA Process

by Arnaud Monpezat, Gabriel Couchaux, Vincent Thomas, Antoine Artheix, Ludovic Deliere, Claire Gréau, Sylvain Topin, Benoit Coasne, Lucian Roiban, Luis Cardenas and David Farrusseng

Catalysts 2019, 9(8), 686; https://doi.org/10.3390/catal9080686 - 14 Aug 2019

Cited by 7 | Viewed by 3804

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 (Ag@ZSM-5) 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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15 pages, 2918 KiB

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

by Guofu Liu, Wenjie Zhang, Pengfei He, Dekui Shen, Chunfei Wu and Chenghong Gong

Catalysts 2019, 9(8), 685; https://doi.org/10.3390/catal9080685 - 13 Aug 2019

Cited by 7 | Viewed by 3544

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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14 pages, 4509 KiB

Open AccessArticle

Improved Hydrothermal Stability in Glass Diesel Soot Oxidation Catalysts

by James Zokoe, Xiaoxiang Feng, Changsheng Su and Paul J. McGinn

Catalysts 2019, 9(8), 684; https://doi.org/10.3390/catal9080684 - 13 Aug 2019

Cited by 4 | Viewed by 2933

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 (ΔG_i) 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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12 pages, 1643 KiB

Open AccessArticle

Performance Analysis of Biocathode in Bioelectrochemical CO₂ Reduction

by Anirudh Bhanu Teja Nelabhotla, Rune Bakke and Carlos Dinamarca

Catalysts 2019, 9(8), 683; https://doi.org/10.3390/catal9080683 - 12 Aug 2019

Cited by 13 | Viewed by 3940

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

(This article belongs to the Special Issue CO₂ Capture and / or Its Transformation into Fuels or Valuable Chemicals)

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15 pages, 4667 KiB

Open AccessArticle

Insights into the Pyrolysis Processes of Ce-MOFs for Preparing Highly Active Catalysts of Toluene Combustion

by Wenjie Sun, Xiaomin Li, Chao Sun, Zhen Huang, Hualong Xu and Wei Shen

Catalysts 2019, 9(8), 682; https://doi.org/10.3390/catal9080682 - 10 Aug 2019

Cited by 66 | Viewed by 9258

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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10 pages, 3868 KiB

Open AccessFeature PaperArticle

Improvement of Photocatalytic H₂-Generation under Visible Light Irradiation by Controlling the Band Gap of ZnIn₂S₄ with Cu and In

by Ikki Tateishi, Mai Furukawa, Hideyuki Katsumata and Satoshi Kaneco

Catalysts 2019, 9(8), 681; https://doi.org/10.3390/catal9080681 - 10 Aug 2019

Cited by 11 | Viewed by 3763

Abstract

The band gap controlled photocatalyst (Zn_0.74Cu_0.13In₂S_3.805) 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 (Zn_0.74Cu_0.13In₂S_3.805) 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 Zn_0.74Cu_0.13In₂S_3.805, which was about five times higher than that of untreated ZnIn₂S₄ under visible light (λ ≥ 420 nm). The band gap of Zn_0.74Cu_0.13In₂S_3.805 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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32 pages, 9254 KiB

Open AccessFeature PaperReview

Insights into the TiO₂-Based Photocatalytic Systems and Their Mechanisms

by Mohan Sakar, Ravikumar Mithun Prakash and Trong-On Do

Catalysts 2019, 9(8), 680; https://doi.org/10.3390/catal9080680 - 9 Aug 2019

Cited by 95 | Viewed by 15103

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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20 pages, 14640 KiB

Open AccessFeature PaperArticle

In Silico Acetylene [2+2+2] Cycloadditions Catalyzed by Rh/Cr Indenyl Fragments

by Shah Masood Ahmad, Marco Dalla Tiezza and Laura Orian

Catalysts 2019, 9(8), 679; https://doi.org/10.3390/catal9080679 - 9 Aug 2019

Cited by 7 | Viewed by 4251

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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18 pages, 5202 KiB

Open AccessArticle

Laboratory and On-Road Evaluation of a GPF-Equipped Gasoline Vehicle

by Ricardo Suarez-Bertoa, Tero Lähde, Jelica Pavlovic, Victor Valverde, Michael Clairotte and Barouch Giechaskiel

Catalysts 2019, 9(8), 678; https://doi.org/10.3390/catal9080678 - 9 Aug 2019

Cited by 25 | Viewed by 4253

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 NO_x 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 Diesel and Gasoline Particulate Filters)

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19 pages, 6237 KiB

Open AccessArticle

High Performance of Mn-Doped MgAlO_x Mixed Oxides for Low Temperature NO_x Storage and Release

by Chenchen Cui, Junwei Ma, Zhongpeng Wang, Wei Liu, Wenxu Liu and Liguo Wang

Catalysts 2019, 9(8), 677; https://doi.org/10.3390/catal9080677 - 9 Aug 2019

Cited by 10 | Viewed by 3224

Abstract

NO_x storage-reduction (NSR) is a potential approach for the effective removal of NO_x under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlO_x) with high performance for low temperature NO_x storage and release were derived from [...] Read more.

NO_x storage-reduction (NSR) is a potential approach for the effective removal of NO_x under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlO_x) with high performance for low temperature NO_x 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 MgAlO_x catalysts exhibited high NO_x 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 NO_x adsorption at 200 °C on Mn15 catalyst (the sample containing 15 wt% of Mn). The in situ DRIFTS spectra of NO_x adsorption proved that the Mn-doped hydrotalcite catalysts are preferred for low temperature NO_x storage and release due to their ability to store NO_x mainly in the form of thermally labile nitrites. NSR cycling tests revealed the NO_x 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 NO_x storage performance of Mn15 catalyst was also studied. In all, owning to their excellent NO_x storage capacity, NSR cycling performance, and resistance to CO₂, soot, SO₂ and H₂O, the Mn-doped MgAlO_x NSR catalysts have broad application prospects in NO_x 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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22 pages, 12929 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Relationship between Reaction Temperature and Carbon Deposition on Nickel Catalysts Based on Al₂O₃, ZrO₂ or SiO₂ Supports during the Biogas Dry Reforming Reaction

by Nikolaos D. Charisiou, Savvas L. Douvartzides, Georgios I. Siakavelas, Lazaros Tzounis, Victor Sebastian, Vlad Stolojan, Steven J. Hinder, Mark A. Baker, Kyriaki Polychronopoulou and Maria A. Goula

Catalysts 2019, 9(8), 676; https://doi.org/10.3390/catal9080676 - 9 Aug 2019

Cited by 76 | Viewed by 7187

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, O^2– 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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18 pages, 3752 KiB

Open AccessArticle

Gel-Type and Macroporous Cross-Linked Copolymers Functionalized with Acid Groups for the Hydrolysis of Wheat Straw Pretreated with an Ionic Liquid

by Giulia Lavarda, Silvia Morales-delaRosa, Paolo Centomo, Jose M. Campos-Martin, Marco Zecca and Jose L. G. Fierro

Catalysts 2019, 9(8), 675; https://doi.org/10.3390/catal9080675 - 8 Aug 2019

Cited by 14 | Viewed by 3286

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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4 pages, 178 KiB

Open AccessEditorial

Catalytic Processes for The Valorization of Biomass Derived Molecules

by Claudia Espro and Francesco Mauriello

Catalysts 2019, 9(8), 674; https://doi.org/10.3390/catal9080674 - 8 Aug 2019

Cited by 3 | Viewed by 2475

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)

18 pages, 4079 KiB

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

by Jan Philipp Burghardt, Markus Baas, Doreen Gerlach and Peter Czermak

Catalysts 2019, 9(8), 673; https://doi.org/10.3390/catal9080673 - 7 Aug 2019

Cited by 11 | Viewed by 5250

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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9 pages, 1753 KiB

Open AccessCommunication

Synthesis of Hierarchical Titanium Silicalite-1 Using a Carbon-Silica-Titania Composite from Xerogel Mild Carbonization

by Xinya Pei, Xiaoxue Liu, Xiaoyu Liu, Jinling Shan, Hui Fu, Ying Xie, Xuemin Yan, Xianzhu Meng, Yancheng Zheng, Geng Li, Qi Wang and Hao Li

Catalysts 2019, 9(8), 672; https://doi.org/10.3390/catal9080672 - 7 Aug 2019

Cited by 10 | Viewed by 3706

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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11 pages, 1037 KiB

Open AccessReview

Microbial Phosphotriesterase: Structure, Function, and Biotechnological Applications

by Wahhida Latip, Victor Feizal Knight, Norhana Abdul Halim, Keat Khim Ong, Noor Azilah Mohd Kassim, Wan Md Zin Wan Yunus, Siti Aminah Mohd Noor and Mohd Shukuri Mohamad Ali

Catalysts 2019, 9(8), 671; https://doi.org/10.3390/catal9080671 - 7 Aug 2019

Cited by 25 | Viewed by 5362

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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13 pages, 1962 KiB

Open AccessArticle

Catalytic Dehydration of Ethanol over WO_x Nanoparticles Supported on MFI (Mobile Five) Zeolite Nanosheets

by Haneul Kim, Muhammad Numan and Changbum Jo

Catalysts 2019, 9(8), 670; https://doi.org/10.3390/catal9080670 - 6 Aug 2019

Cited by 6 | Viewed by 3946

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 WO_x nanoparticles were homogeneously distributed over the entire void space of nanosheet samples up to a loading of 2 mol %, after which large WO_x nanoparticles with needle-like morphology were formed on the surface of the zeolite nanosheet beyond 2mol%. The number of acid sites increased with WO_x loading and, as a result, EtOH conversion progressively increased with WO_x loading up to 6 mol %. At reaction temperatures of >390 °C, homogeneously distributed WO_x nanoparticles showed slightly higher ethylene selectivity than nano-needle structured WO_x. However, nano-needle structured WO_x exhibited greater catalytic stability. In terms of ethylene yield over 8 h, needle-like WO_x nanoparticles were found to be more suitable for the acid-catalyzed dehydration of ethanol than small-sized WO_x nanoparticles. Full article

(This article belongs to the Special Issue Synthesis and Application of Zeolite Catalysts)

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15 pages, 6645 KiB

Open AccessArticle

In situ Decolorization Monitoring of Textile Dyes for an Optimized UV-LED/TiO₂ Reactor

by Tecilli Tapia-Tlatelpa, Jose Trull and Luis Romeral

Catalysts 2019, 9(8), 669; https://doi.org/10.3390/catal9080669 - 6 Aug 2019

Cited by 12 | Viewed by 3752

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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Catalysts, Volume 9, Issue 8 (August 2019) – 68 articles

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