Catalysts

15 pages, 6617 KiB

Open AccessArticle

Sustainable Hydrogen Production from Starch Aqueous Suspensions over a Cd_0.7Zn_0.3S-Based Photocatalyst

by Anna Y. Kurenkova, Tatiana B. Medvedeva, Nikolay V. Gromov, Andrey V. Bukhtiyarov, Evgeny Y. Gerasimov, Svetlana V. Cherepanova and Ekaterina A. Kozlova

Catalysts 2021, 11(7), 870; https://doi.org/10.3390/catal11070870 - 20 Jul 2021

Cited by 8 | Viewed by 3018

Abstract

We explored the photoreforming of rice and corn starch with simultaneous hydrogen production over a Cd_0.7Zn_0.3S-based photocatalyst under visible light irradiation. The photocatalyst was characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The influence of [...] Read more.

We explored the photoreforming of rice and corn starch with simultaneous hydrogen production over a Cd_0.7Zn_0.3S-based photocatalyst under visible light irradiation. The photocatalyst was characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The influence of starch pretreatment conditions, such as hydrolysis temperature and alkaline concentration, on the reaction rate was studied. The maximum rate of H₂ evolution was 730 μmol·h⁻¹·g⁻¹, with AQE = 1.8% at 450 nm, in the solution obtained after starch hydrolysis in 5 M NaOH at 70 °C. The composition of the aqueous phase of the suspension before and after the photocatalytic reaction was studied via high-performance liquid chromatography, and such products as glucose and sodium gluconate, acetate, formate, glycolate, and lactate were found after the photocatalytic reaction. Full article

(This article belongs to the Special Issue Innovative and Practical Trends in Photocatalytic Degradation of Environmental Pollutants)

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21 pages, 6484 KiB

Open AccessReview

Conversion of Green Methanol to Methyl Formate

by Doreen Kaiser, Luise Beckmann, Jan Walter and Martin Bertau

Catalysts 2021, 11(7), 869; https://doi.org/10.3390/catal11070869 - 20 Jul 2021

Cited by 36 | Viewed by 10762

Abstract

Methyl formate is a key component for both defossilized industry and mobility. The current industrial production via carbonylation of methanol has various disadvantages such as high requirements on reactant purity and low methanol conversion rates. In addition, there is a great interest in [...] Read more.

Methyl formate is a key component for both defossilized industry and mobility. The current industrial production via carbonylation of methanol has various disadvantages such as high requirements on reactant purity and low methanol conversion rates. In addition, there is a great interest in replacing the conventional homogeneous catalyst with a heterogeneous one, among other things to improve the downstream processing. This is why new approaches for methyl formate are sought. This review summarizes promising approaches for methyl formate production using methanol as a reactant. Full article

(This article belongs to the Special Issue New Catalysts and Reactors for the Synthesis or Conversion of Methanol)

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10 pages, 2422 KiB

Open AccessFeature PaperArticle

Highly Efficient Visible Light Photodegradation of Cr(VI) Using Electrospun MWCNTs-Fe₃O₄@PES Nanofibers

by Alaa Mohamed, Samy Yousef, Shady Ali, Mantas Sriubas, Sarunas Varnagiris, Simona Tuckute, Mohammed Ali Abdelnaby and Bahaa M. Kamel

Catalysts 2021, 11(7), 868; https://doi.org/10.3390/catal11070868 - 20 Jul 2021

Cited by 15 | Viewed by 2913

Abstract

The development of highly efficient photocatalysis has been prepared by two different methods for the photodegradation of Cr(VI) from an aqueous solution under visible light. The electrospun polyethersulfone (PES)/iron oxide (Fe₃O₄) and multi-wall carbon nanotubes (MWCNTs) composite nanofibers have [...] Read more.

The development of highly efficient photocatalysis has been prepared by two different methods for the photodegradation of Cr(VI) from an aqueous solution under visible light. The electrospun polyethersulfone (PES)/iron oxide (Fe₃O₄) and multi-wall carbon nanotubes (MWCNTs) composite nanofibers have been prepared using the electrospinning technique. The prepared materials were characterized by SEM and XRD analysis. The result reveals the successful fabrication of the composite nanofiber with uniformly and smooth nanofibers. The effect of numerous parameters were explored to investigate the effects of pH value, contact time, concentration of Cr(VI), and reusability. The MWCNTs-Fe₃O₄@PES composite nanofibers exhibited excellent photodegradation of Cr(VI) at pH 2 in 80 min. The photocatalysis materials are highly stable without significant reduction of the photocatalytic efficiency of Cr(VI) after five cycles. Therefore, due to its easy separation and reuse without loss of photocatalytic efficiency, the photocatalysis membrane has tremendous potential for the removal of heavy metals from aqueous solutions. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalysis Technology in Europe and Asia)

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25 pages, 32299 KiB

Open AccessFeature PaperReview

Mild Oxidation of Organosulfur Compounds with H₂O₂ over Metal-Containing Microporous and Mesoporous Catalysts

by Vasile Hulea, Emil Dumitriu and François Fajula

Catalysts 2021, 11(7), 867; https://doi.org/10.3390/catal11070867 - 20 Jul 2021

Cited by 8 | Viewed by 3840

Abstract

Mild catalytic oxidation of thioethers and thiophenes is an important reaction for the synthesis of molecules with pharmaceutical interest, as well as for the development of efficient processes able to remove sulfur-containing pollutants from fuels and wastewater. With respect to the green chemistry [...] Read more.

Mild catalytic oxidation of thioethers and thiophenes is an important reaction for the synthesis of molecules with pharmaceutical interest, as well as for the development of efficient processes able to remove sulfur-containing pollutants from fuels and wastewater. With respect to the green chemistry principles, hydrogen peroxide (H₂O₂) is the ideal oxidant and the Me-containing porous materials (Me = Ti, V, Mo, W, Zr) are among the best heterogeneous catalysts for these applications. The main classes of catalysts, including Me-microporous and mesoporous silicates, Me-layered double hydroxides, Me-metal–organic frameworks, are described in this review. The catalytic active species generated in the presence of H₂O₂, as well as the probable oxidation mechanisms, are also addressed. The reactivity of molecules in the sulfoxidation process and the role played by the solvents are explored. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Feature Papers in Nanostructured Catalysts)

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9 pages, 1250 KiB

Open AccessCommunication

Encapsulation of Combi-CLEAs of Glycosidases in Alginate Beads and Polyvinyl Alcohol for Wine Aroma Enhancement

by Luigi Tavernini, Carla Aburto, Oscar Romero, Andrés Illanes and Lorena Wilson

Catalysts 2021, 11(7), 866; https://doi.org/10.3390/catal11070866 - 20 Jul 2021

Cited by 5 | Viewed by 2196

Abstract

The aromatic expression of wines can be enhanced by the addition of specific glycosidases, although their poor stability remains a limitation. Coimmobilization of glycosidases as cross-linked enzyme aggregates (combi-CLEAs) offers a simple solution yielding highly stable biocatalysts. Nevertheless, the small particle size of [...] Read more.

The aromatic expression of wines can be enhanced by the addition of specific glycosidases, although their poor stability remains a limitation. Coimmobilization of glycosidases as cross-linked enzyme aggregates (combi-CLEAs) offers a simple solution yielding highly stable biocatalysts. Nevertheless, the small particle size of combi-CLEAs hinders their recovery, preventing their industrial application. Encapsulation of combi-CLEAs of glycosidases in alginate beads and in polyvinyl alcohol is proposed as a solution. Combi-CLEAS of β-d-glucosidase and α-l-arabinofuranosidase were prepared and encapsulated. The effects of combi-CLEA loading and particle size on the expressed specific activity (IU/g_biocatalyst) of the biocatalysts were evaluated. Best results were obtained with 2.6 mm diameter polyvinyl alcohol particles at a loading of 60 mg_combi-CLEA/g_{polyvinyl alcohol}, exhibiting activities of 1.9 and 1.0 IU/g_biocatalyst for β-d-glucosidase and α-l-arabinofuranosidase, respectively. Afterwards, the stability of the biocatalysts was tested in white wine. All the encapsulated biocatalysts retained full activity after 140 incubation days, outperforming both free enzymes and nonencapsulated combi-CLEAs. Nevertheless, the alginate-encapsulated biocatalysts showed a brittle consistency, making recovery unfeasible. Conversely, the polyvinyl-encapsulated biocatalyst remained intact throughout the assay. The encapsulation of combi-CLEAs in polyvinyl alcohol proved to be a simple methodology that allows their recovery and reuse to harness their full catalytic potential. Full article

(This article belongs to the Special Issue Multienzymatic Catalysis and/or Enzyme Co-immobilization)

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10 pages, 2772 KiB

Open AccessArticle

Enhanced SO₂ Absorption Capacity of Sodium Citrate Using Sodium Humate

by Zhiguo Sun, Yue Zhou, Shichao Jia, Yaru Wang, Dazhan Jiang and Li Zhang

Catalysts 2021, 11(7), 865; https://doi.org/10.3390/catal11070865 - 20 Jul 2021

Cited by 5 | Viewed by 2729

Abstract

A novel method of improving the SO₂ absorption performance of sodium citrate (Ci-Na) using sodium humate (HA–Na) as an additive was put forward. The influence of different Ci-Na concentration, inlet SO₂ concentration and gas flow rate on desulfurization performance were studied. [...] Read more.

A novel method of improving the SO₂ absorption performance of sodium citrate (Ci-Na) using sodium humate (HA–Na) as an additive was put forward. The influence of different Ci-Na concentration, inlet SO₂ concentration and gas flow rate on desulfurization performance were studied. The synergistic mechanism of SO₂ absorption by HA–Na and Ci-Na was also analyzed. The consequence shows that the efficiency of SO₂ absorption by Ci-Na is above 90% and the desulfurization time added with the Ci-Na concentration rising from 0.01 to 0.1 mol/L. Both the desulfurization efficiency and time may increase with the adding of HA–Na quality in Ci-Na solution. Due to adding HA–Na, the desulfurization efficiency of Ci-Na increased from 90% to 99% and the desulfurization time increased from 40 to 55 min. Under the optimum conditions, the desulfurization time of Ci-Na can exceed 70 min because of adding HA–Na, which is nearly doubled. The growth of inlet SO₂ concentration has little effect on the desulfurization efficiency. The SO₂ adsorption efficiency decreases with the increase of inlet flow gas. The presence of O₂ improves the SO₂ removal efficiency and prolongs the desulfurization time. Therefore, HA–Na plays a key role during SO₂ absorption and can dramatically enhance the SO₂ adsorption performance of Ci-Na solution. Full article

(This article belongs to the Special Issue Environmental Friendly Catalysts for Energy and Pollution Control Applications)

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14 pages, 5752 KiB

Open AccessArticle

Plasma-Catalytic Process of Hydrogen Production from Mixture of Methanol and Water

by Bogdan Ulejczyk, Łukasz Nogal, Paweł Jóźwik, Michał Młotek and Krzysztof Krawczyk

Catalysts 2021, 11(7), 864; https://doi.org/10.3390/catal11070864 - 19 Jul 2021

Cited by 14 | Viewed by 3450

Abstract

In the present work the process of hydrogen production was conducted in the plasma-catalytic reactor, the substrates were first treated with plasma and then introduced into the catalyst bed. Plasma was produced by a spark discharge. The discharge power ranged from 15 to [...] Read more.

In the present work the process of hydrogen production was conducted in the plasma-catalytic reactor, the substrates were first treated with plasma and then introduced into the catalyst bed. Plasma was produced by a spark discharge. The discharge power ranged from 15 to 46 W. The catalyst was metallic nickel supported on Al₂O₃. The catalyst was active from a temperature of 400 °C. The substrate flow rate was 1 mol/h of water and 1 mol/h of methanol. The process generated H₂, CO, CO₂ and CH₄. The gas which formed the greatest amount was H₂. Its concentration in the gas was ~60%. The conversion of methanol and the production of hydrogen in the plasma-catalytic reactor were higher than in the plasma and catalytic reactors. The synergy effect of the interaction of two environments, i.e., plasma and the catalyst, was observed. The highest hydrogen production was 1.38 mol/h and the highest methanol conversion was 64%. The increased in the discharge power resulted in increasing methanol conversion and hydrogen production. Full article

(This article belongs to the Special Issue Towards Catalysts Prepared by Cold Plasma)

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11 pages, 5348 KiB

Open AccessArticle

Selective Oxidation of Cinnamyl Alcohol to Cinnamaldehyde over Functionalized Multi-Walled Carbon Nanotubes Supported Silver-Cobalt Nanoparticles

by Zahoor Iqbal, Muhammad Sufaid Khan, Rozina Khattak, Tausif Iqbal, Ivar Zekker, Muhammad Zahoor, Helal F. Hetta, Gaber El-Saber Batiha and Eida M. Alshammari

Catalysts 2021, 11(7), 863; https://doi.org/10.3390/catal11070863 - 19 Jul 2021

Cited by 8 | Viewed by 3719

Abstract

The selective oxidation of alcohols to aldehydes has attracted a lot of attention because of its potential use in agrochemicals, fragrances, and fine chemicals. However, due to homogenous catalysis, low yield, low selectivity, and hazardous oxidants, traditional approaches have lost their efficiency. The [...] Read more.

The selective oxidation of alcohols to aldehydes has attracted a lot of attention because of its potential use in agrochemicals, fragrances, and fine chemicals. However, due to homogenous catalysis, low yield, low selectivity, and hazardous oxidants, traditional approaches have lost their efficiency. The co-precipitation method was used to synthesize the silver-cobalt bimetallic catalyst supported on functionalized multi-walled carbon nanotubes (Ag-Co/S). Brunauer Emmet Teller (BET), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) were used to characterize the catalyst. For the oxidation of cinnamyl alcohol (CA) with O₂ as an oxidant, the catalyst’s selectivity and activity were investigated. The impacts of several parameters on catalyst’s selectivity and activity, such as time, temperature, solvents, catalyst dosage, and stirring speed, were comprehensively studied. The results revealed that in the presence of Ag-Co/S as a catalyst, O₂ could be employed as an effective oxidant for the catalytic oxidation of cinnamyl alcohol to cinnamaldehyde (CD) with 99% selectivity and 90% conversion. In terms of cost effectiveness, catalytic activity, selectivity, and recyclability, Ag-Co/S outperforms the competition. As a result, under the green chemistry methodology, it can be utilized as an effective catalyst for the conversion of CA to CD. Full article

(This article belongs to the Special Issue Oxidation Catalysis under Unconventional Methods)

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13 pages, 1483 KiB

Open AccessArticle

A Thermophilic GH5 Endoglucanase from Aspergillus fumigatus and Its Synergistic Hydrolysis of Mannan-Containing Polysaccharides

by Xinxi Gu, Haiqiang Lu, Lijuan Zhang and Xiangchen Meng

Catalysts 2021, 11(7), 862; https://doi.org/10.3390/catal11070862 - 19 Jul 2021

Cited by 5 | Viewed by 2981

Abstract

In this study, we isolated and identified a thermophilic strain of Aspergillus fumigatus from the “Daqu” samples. Transcriptomic analysis of A. fumigatus identified 239 carbohydrate-active enzymes (CAZy)-encoding genes, including 167 glycoside hydrolase (GH)-encoding genes, 58 glycosyltransferase (GT)-encoding genes, 2 polysaccharide lyase (PLs)-encoding genes [...] Read more.

In this study, we isolated and identified a thermophilic strain of Aspergillus fumigatus from the “Daqu” samples. Transcriptomic analysis of A. fumigatus identified 239 carbohydrate-active enzymes (CAZy)-encoding genes, including 167 glycoside hydrolase (GH)-encoding genes, 58 glycosyltransferase (GT)-encoding genes, 2 polysaccharide lyase (PLs)-encoding genes and 12 carbohydrate esterase (CEs)-encoding genes, which indicates that the strain has a strong potential for application for enzyme production. Furthermore, we also identified a novel endoglucanase gene (AfCel5A), which was expressed in Pichia pastoris and characterized. The novel endoglucanase AfCel5A exhibited the highest hydrolytic activity against CMC-Na and the optimal activity at 80 °C and pH 4.0 and also showed good stability at pH 3.0–11.0 and below 70 °C. The Km and Vmax values of AfCel5 were 0.16 ± 0.05 mg·mL⁻¹ and 7.23 ± 0.33 mol mg⁻¹·min⁻¹, respectively, using CMC-Na as a substrate. Further, the endoglucanase exhibited a high tolerance toward NaCl as well as glucose. In addition, the finding that the endoglucanase AfCel5A in combination with β-mannanse (ManBK) clearly increased the release of total reducing sugars of glucomannan by up to 74% is significant. Full article

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21 pages, 3153 KiB

Open AccessFeature PaperReview

Heterogeneous Catalysts for the Conversion of Glucose into 5-Hydroxymethyl Furfural

by Christiaan H. L. Tempelman, Ryan Oozeerally and Volkan Degirmenci

Catalysts 2021, 11(7), 861; https://doi.org/10.3390/catal11070861 - 19 Jul 2021

Cited by 34 | Viewed by 6073

Abstract

Lignocellulosic biomass, a cheap and plentiful resource, could play a key role in the production of sustainable chemicals. The simple sugars contained in the renewable lignocellulosic biomass can be converted into commercially valuable products such as 5-hydroxymethyl furfural (HMF). A platform molecule, HMF [...] Read more.

Lignocellulosic biomass, a cheap and plentiful resource, could play a key role in the production of sustainable chemicals. The simple sugars contained in the renewable lignocellulosic biomass can be converted into commercially valuable products such as 5-hydroxymethyl furfural (HMF). A platform molecule, HMF can be transformed into numerous chemical products with potential applications in a wide variety of industries. Of the hexoses contained in the lignocellulosic biomass, the successful production of HMF from glucose has been a challenge. Various heterogeneous catalysts have been proposed over the last decade, ranging from zeolites to metal organic frameworks. The reaction conditions vary in the reports in the literature, which makes it difficult to compare catalysts reported in different studies. In addition, the slight variations in the synthesis of the same material in different laboratories may affect the activity results, because the selectivity towards desired products in this transformation strongly depends on the nature of the active sites. This poses another difficulty for the comparison of different reports. Furthermore, over the last decade the new catalytic systems proposed have increased profoundly. In this article, we summarize the heterogeneous catalysts: Metal Organic Frameworks (MOFs), zeolites and conventional supported catalysts, that have been reported in the recent literature and provide an overview of the observed catalytic activity, in order to provide a comparison. Full article

(This article belongs to the Special Issue Advances in Catalysis for Fuel and Chemical Production from Biomass Feedstocks)

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8 pages, 1780 KiB

Open AccessArticle

Decomposition of Tars on a Nickel Honeycomb Catalyst

by Joanna Woroszył-Wojno, Michał Młotek, Michalina Perron, Paweł Jóźwik, Bogdan Ulejczyk and Krzysztof Krawczyk

Catalysts 2021, 11(7), 860; https://doi.org/10.3390/catal11070860 - 19 Jul 2021

Cited by 2 | Viewed by 2908

Abstract

Biomass can be considered a renewable energy source. It undergoes a gasification process to obtain gaseous fuel, which converts it into combustible gaseous products such as hydrogen, carbon monoxide, and methane. The process also generates undesirable tars that can condense in gas lines [...] Read more.

Biomass can be considered a renewable energy source. It undergoes a gasification process to obtain gaseous fuel, which converts it into combustible gaseous products such as hydrogen, carbon monoxide, and methane. The process also generates undesirable tars that can condense in gas lines and cause corrosion, and after processing, can be an additional source of combustible gases. This study focused on the processing of tar substances with toluene as a model substance. The effect of discharge power and carrier gas composition on toluene conversion was tested. The process was conducted in a plasma-catalytic system with a new Ni₃Al system in the form of a honeycomb. The toluene conversion reached 90%, and small amounts of ethane, ethylene, acetylene, benzene, and C₃ and C₄ hydrocarbons were detected in the post-reaction mixture. Changes in the surface composition of the Ni₃Al catalyst were observed throughout the experiments. These changes did not affect the toluene conversion. Full article

(This article belongs to the Special Issue Towards Catalysts Prepared by Cold Plasma)

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11 pages, 1871 KiB

Open AccessArticle

An Investigation into the Bulk and Surface Phase Transformations of Bimetallic Pd-In/Al₂O₃ Catalyst during Reductive and Oxidative Treatments In Situ

by Nadezhda S. Smirnova, Evgeny V. Khramov, Galina N. Baeva, Pavel V. Markov, Andrey V. Bukhtiyarov, Yan V. Zubavichus and Aleksander Y. Stakheev

Catalysts 2021, 11(7), 859; https://doi.org/10.3390/catal11070859 - 18 Jul 2021

Cited by 5 | Viewed by 2826

Abstract

A series of oxidative treatments of PdIn-supported intermetallic nanoparticles at different temperatures were performed. The bulk and surface structure of catalyst during phase transformation was investigated by bulk- and surface-sensitive techniques (in situ XAFS, DRIFTS of adsorbed CO). It was found that comparison [...] Read more.

A series of oxidative treatments of PdIn-supported intermetallic nanoparticles at different temperatures were performed. The bulk and surface structure of catalyst during phase transformation was investigated by bulk- and surface-sensitive techniques (in situ XAFS, DRIFTS of adsorbed CO). It was found that comparison of palladium and indium fractions in bulk and on the surface suggests the formation of a «core-shell» structure. According to obtained results, the core consists of In-depleted intermetallic compound or inhomogeneous bimetallic phase with the inner core of metallic Pd, when a mixture of indium oxide, metallic palladium and small part of PdIn is present on the surface. Full article

(This article belongs to the Special Issue Mono- and Bimetallic Nanoparticles in Catalysis)

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11 pages, 4222 KiB

Open AccessArticle

Direct Cross-Coupling of Alcohols with O-Nucleophiles Mediated by N-Iodosuccinimide as a Precatalyst under Mild Reaction Conditions

by Njomza Ajvazi and Stojan Stavber

Catalysts 2021, 11(7), 858; https://doi.org/10.3390/catal11070858 - 17 Jul 2021

Cited by 2 | Viewed by 3186

Abstract

We report N-iodosuccinimide as the most efficient and selective precatalyst among the N-halosuccinimides for dehydrative O-alkylation reactions between various alcohols under high-substrate concentration reaction conditions. The protocol is non-metal, one-pot, selective, and easily scalable, with excellent yields; enhancing the green [...] Read more.

We report N-iodosuccinimide as the most efficient and selective precatalyst among the N-halosuccinimides for dehydrative O-alkylation reactions between various alcohols under high-substrate concentration reaction conditions. The protocol is non-metal, one-pot, selective, and easily scalable, with excellent yields; enhancing the green chemical profiles of these transformations. Full article

(This article belongs to the Special Issue Current State-of-the-Art of Catalysts)

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14 pages, 4257 KiB

Open AccessFeature PaperArticle

Thermal Treatment of Polyvinyl Alcohol for Coupling MoS₂ and TiO₂ Nanotube Arrays toward Enhancing Photoelectrochemical Water Splitting Performance

by Tho Truong Nguyen, Thi Minh Cao, Narmina O. Balayeva and Viet Van Pham

Catalysts 2021, 11(7), 857; https://doi.org/10.3390/catal11070857 - 17 Jul 2021

Cited by 17 | Viewed by 3594

Abstract

Solar-driven photoelectrochemical (PEC) water splitting, using semiconductor photoelectrodes, is considered a promising renewable energy source and solution for environmental sustainability. Herein, we report polyvinyl alcohol (PVA) as a binder material for combining MoS₂ and TiO₂ nanotube arrays (TNAs) to improve PEC [...] Read more.

Solar-driven photoelectrochemical (PEC) water splitting, using semiconductor photoelectrodes, is considered a promising renewable energy source and solution for environmental sustainability. Herein, we report polyvinyl alcohol (PVA) as a binder material for combining MoS₂ and TiO₂ nanotube arrays (TNAs) to improve PEC water splitting ability. By a thermal treatment process, the formation of the π conjunction in the PVA structure enhanced the PEC performance of MoS₂/TNAs, exhibiting linear sweeps in an anodic direction with the current density over 65 μA/cm² at 0 V vs. Ag/AgCl. Besides, the photoresponse ability of MoS₂/TNAs is approximately 6-fold more significant than that of individual TNAs. Moreover, a Tafel slope of 140.6 mV/decade has been obtained for the oxygen evolution reaction (OER) of MoS₂/TNAs materials. Full article

(This article belongs to the Special Issue Recent Advances in Visible-Light-Driven Heterogeneous Photocatalysis)

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12 pages, 5029 KiB

Open AccessArticle

Fabrication of Six Manganese Containing Polyoxometalate Modified Graphite C₃N₄ Nanosheets Catalysts Used to Catalyze Water Decomposition

by Yue Wu, Xiaoxia Yu, Zhijing Fu, Jianye Pei and Lihua Bi

Catalysts 2021, 11(7), 856; https://doi.org/10.3390/catal11070856 - 17 Jul 2021

Cited by 6 | Viewed by 2543

Abstract

With the increase in gas population, the demand for clean and renewable energy is increasing. Hydrogen energy has a high combustion conversion energy while water is its combustion product. In recent years, a way to convert water into hydrogen and oxygen has been [...] Read more.

With the increase in gas population, the demand for clean and renewable energy is increasing. Hydrogen energy has a high combustion conversion energy while water is its combustion product. In recent years, a way to convert water into hydrogen and oxygen has been found by human beings inspired by plant photosynthesis. However, water decomposition consumes a significant amount of energy and is expensive. People expect to obtain a water decomposition catalyst with low cost and high efficiency. This work selected a six-manganese containing polyoxometalate with a similar structure characteristic to photosynthesizing PSII to fabricate with graphite C₃N₄ nanosheets for the construction of composite film (Mn₆SiW/g-C₃N₄NSs) electrode via layer by layer self-assembly technology, which was used for the photo-electrochemical decomposition of water under visible light conditions. The binary composite film electrode displayed good catalytic efficiency. The photoelectric density of the composite electrode is 46 μA/cm² (at 1.23 V vs. Ag/AgCl) and 239 μA/cm² (at 1.5 V vs. Ag/AgCl). Compared with the g-C₃N₄NSs electrode alone, the photoelectric density of the composite electrode increased by 1 time. The reason is attributed to the fact that Mn₆SiW has a similar structure characteristic to photosynthesizing PSII and high electron transferability. The construction of the composite film containing low-cost Mn₆SiW to modify g-C₃N₄NSs can effectively improve the photocatalytic decomposition of water, thus this study provides valuable reference information for the development of low-cost and high-performance photo-electrocatalytic materials. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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17 pages, 3829 KiB

Open AccessArticle

Photocatalytic Treatment of Wastewater Containing Simultaneous Organic and Inorganic Pollution: Competition and Operating Parameters Effects

by Ahmed Amine Azzaz, Salah Jellali, Nasser Ben Harharah Hamed, Atef El Jery, Lotfi Khezami, Aymen Amine Assadi and Abdeltif Amrane

Catalysts 2021, 11(7), 855; https://doi.org/10.3390/catal11070855 - 16 Jul 2021

Cited by 28 | Viewed by 2597

Abstract

In the present study, methylene blue (MB) removal from aqueous solutions via the photocatalytic process using TiO₂ as a catalyst in the presence of external ultra-violet light (UV) was investigated. The results of adsorption in the absence of UV radiation showed that [...] Read more.

In the present study, methylene blue (MB) removal from aqueous solutions via the photocatalytic process using TiO₂ as a catalyst in the presence of external ultra-violet light (UV) was investigated. The results of adsorption in the absence of UV radiation showed that adsorption reached an equilibrium state at 60 min. The experimental kinetic data were found to be well fitted by the pseudo-second-order model. Furthermore, the isotherm study suggested that dye uptake by TiO₂ is a chemisorption process with a maximum retention capacity of 34.0 mg/g. The photodegradation of MB was then assessed under various experimental conditions. The related data showed that dye mineralization decreased when dye concentrations were increased and was favored at high pH values and low salt concentrations. The simultaneous presence of organic and inorganic pollution (Zinc) was also evaluated. The effect of the molar ratio Zn²⁺/MB⁺ in the solution at different pH values and NaCl concentrations was also monitored. The corresponding experimental results showed that at low values of Zn²⁺ in the solution (30 mg/L), the kinetic of the MB removal became faster until reaching an optimum at Zn²⁺/MB⁺ concentrations of 60/60 mg/L; it then slowed down for higher concentrations. The solutions’ carbon contents were measured during the degradation process and showed total mineralization after about 5 h for the optimal Zn²⁺/MB⁺ condition. Full article

(This article belongs to the Special Issue Photoelectrochemical and Photocatalytic Performance: Catalysts for Renewable Energy Production and Wastewater Remediation)

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15 pages, 6378 KiB

Open AccessFeature PaperArticle

Perovskite Zinc Titanate Photocatalysts Synthesized by the Sol–Gel Method and Their Application in the Photocatalytic Degradation of Emerging Contaminants

by Wei-Yu Chen, Ching-Ping Wang, Po-Chou Chen, Kun-Yi Andrew Lin, Surajit Ghosh, Chao-Wei Huang and Van-Huy Nguyen

Catalysts 2021, 11(7), 854; https://doi.org/10.3390/catal11070854 - 16 Jul 2021

Cited by 26 | Viewed by 4635

Abstract

In this study, perovskite ZnTiO₃ photocatalysts were fabricated by the sol–gel method. The photocatalytic capability was verified by the degradation of the emerging contaminant, the antibiotic amoxicillin (AMX). For the preparation, the parameters of the calcination temperature and the additional amount of [...] Read more.

In this study, perovskite ZnTiO₃ photocatalysts were fabricated by the sol–gel method. The photocatalytic capability was verified by the degradation of the emerging contaminant, the antibiotic amoxicillin (AMX). For the preparation, the parameters of the calcination temperature and the additional amount of polyvinylpyrrolidone (PVP) and ammonia are discussed, including the calcining temperature (500, 600, 700, 800 °C), the volume of ammonia (750, 1500, 3000 μL), and the weight of PVP (3 g and 5 g). The prepared perovskite ZnTiO₃ was characterized by XRD, FESEM, BET, and UV-Vis. It is shown that the perovskite ZnTiO₃ photocatalysts are structurally rod-like and ultraviolet light-responsive. Consequently, the synthesis conditions for fabricating the perovskite ZnTiO₃ photocatalysts with the highest photocatalytic performance were a calcining temperature of 700 °C, an additional ammonia amount of 1500 μL, and added PVP of 5 g. Moreover, the photocatalytic degradation of perovskite ZnTiO₃ photocatalysts on other pollutants, including the antibiotic tetracycline (TC), methyl orange (MO), and methylene blue (MB) dyes, was also examined. This provides the basis for the application of perovskite ZnTiO₃ as a photocatalyst to decompose emerging contaminants and organic pollutants in wastewater treatment. Full article

(This article belongs to the Special Issue Recent Advances in Catalytic Materials toward Renewable Energy and the Removal of Environmental Pollutants)

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13 pages, 7451 KiB

Open AccessArticle

Sustainable Production of Glycolipids by Biocatalyst on Renewable Deep Eutectic Solvents

by Laura V. Hoyos, Laura Ramírez, Cristhian J. Yarce, Carlos Alvarez-Vasco and Nelson H. Caicedo Ortega

Catalysts 2021, 11(7), 853; https://doi.org/10.3390/catal11070853 - 16 Jul 2021

Cited by 4 | Viewed by 3124

Abstract

Glycolipids have become an ecofriendly alternative to chemically obtained surfactants, mainly for the cosmetic, pharmaceutical, and food industries. However, the sustainable production of these compounds is still challenging, because: (i) water is a recognized inhibitor, (ii) multiphases make the [...] Read more.

Glycolipids have become an ecofriendly alternative to chemically obtained surfactants, mainly for the cosmetic, pharmaceutical, and food industries. However, the sustainable production of these compounds is still challenging, because: (i) water is a recognized inhibitor, (ii) multiphases make the use of cosolvent reaction medium necessary, and (iii) there are difficulties in finding a source for both starting materials. This study used sugars and lipids from peach palm fruit shells or model compounds as substrates to synthesize glycolipids on five different renewable deep eutectic solvents (Re-DES) alone or with a cosolvent system. Substrate conversions up to 24.84% (so far, the highest reported for this reaction on DES), showing (1) the non-precipitation of glucose in the solvent, (2) emulsification and (3) low viscosity (e.g., more favorable mass transfer) as the main limiting factors for these heterogeneous enzymatic processes. The resulting conversion was reached using a cosolvent system Re-DES:DMSO:t-butanol that was robust enough to allow conversions in the range 19–25%, using either model compounds or sugar and fatty acid extracts, with free or immobilized enzymes. Finally, the characterization of the in-house synthesized glycolipids by surface tension demonstrated their potential as biosurfactants, for instance, as an alternative to alcohol ethoxylates, industrially produced using less sustainable methods. Full article

(This article belongs to the Special Issue Recent Advances in Ionic Liquids and Deep Eutectic Solvents for Task-Specific Catalysts)

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13 pages, 3259 KiB

Open AccessArticle

Quarry Residue: Treatment of Industrial Effluent Containing Dye

by Lariana Negrão Beraldo de Almeida, Tatiana Gulminie Josué, Othavio Henrique Lupepsa Nogueira, Daniele Toniolo Dias, Angelo Marcelo Tusset, Onélia Aparecida Andreo dos Santos and Giane Gonçalves Lenzi

Catalysts 2021, 11(7), 852; https://doi.org/10.3390/catal11070852 - 16 Jul 2021

Cited by 1 | Viewed by 2617

Abstract

This work is devoted to the investigation of the discoloration of the synthetic and industrial effluent, using a quarry residue (MbP), which is a material naturally composed of mixed oxides, compared to zinc oxide (ZnO), acting as photocatalysts and adsorbents. The optimization of [...] Read more.

This work is devoted to the investigation of the discoloration of the synthetic and industrial effluent, using a quarry residue (MbP), which is a material naturally composed of mixed oxides, compared to zinc oxide (ZnO), acting as photocatalysts and adsorbents. The optimization of the pH and catalyst concentration parameters was carried out, and the industrial effluent was then treated by photocatalytic reactions, adsorption, and photolysis. Industrial effluent was supplied by a packaging company and was collected for a period of seven consecutive days, showing the oscillation of the parameters in the process. The material characterizations were obtained by scanning electron microscopy (SEM-EDS), X-Ray diffraction (XRD), and photoacoustic spectroscopy (PAS). The results indicated that the composition of the quarry waste is mainly silica and has E_gap 2.16 eV. The quarry residue as photocatalyst was active for the artificial effluent (synthetic dye solution), with a maximum of 98% discoloration, and as an adsorbent for industrial effluent, with a maximum of 57% of discoloration. Although the quarry residue has shown results lower than ZnO, it is considered a promising material in adsorption processes and photocatalytic reactions for discoloration of aqueous solutions. Full article

(This article belongs to the Special Issue Photocatalysis in the Wastewater Treatment)

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21 pages, 388 KiB

Open AccessReview

Exogenous Enzymes as Zootechnical Additives in Animal Feed: A Review

by Brianda Susana Velázquez-De Lucio, Edna María Hernández-Domínguez, Matilde Villa-García, Gerardo Díaz-Godínez, Virginia Mandujano-Gonzalez, Bethsua Mendoza-Mendoza and Jorge Álvarez-Cervantes

Catalysts 2021, 11(7), 851; https://doi.org/10.3390/catal11070851 - 15 Jul 2021

Cited by 48 | Viewed by 10166

Abstract

Enzymes are widely used in the food industry. Their use as a supplement to the raw material for animal feed is a current research topic. Although there are several studies on the application of enzyme additives in the animal feed industry, it is [...] Read more.

Enzymes are widely used in the food industry. Their use as a supplement to the raw material for animal feed is a current research topic. Although there are several studies on the application of enzyme additives in the animal feed industry, it is necessary to search for new enzymes, as well as to utilize bioinformatics tools for the design of specific enzymes that work in certain environmental conditions and substrates. This will allow the improvement of the productive parameters in animals, reducing costs and making the processes more efficient. Technological needs have considered these catalysts as essential in many industrial sectors and research is constantly being carried out to optimize their use in those processes. This review describes the enzymes used in animal nutrition, their mode of action, their production and new sources of production as well as studies on different animal models to evaluate their effect on the productive performance intended for the production of animal feed. Full article

(This article belongs to the Special Issue Enzymes and Biocatalysis)

19 pages, 3869 KiB

Open AccessFeature PaperArticle

Oxidation of Sulfamethoxazole by Rice Husk Biochar-Activated Persulfate

by Efstathios Avramiotis, Zacharias Frontistis, Ioannis D. Manariotis, John Vakros and Dionissios Mantzavinos

Catalysts 2021, 11(7), 850; https://doi.org/10.3390/catal11070850 - 15 Jul 2021

Cited by 41 | Viewed by 4610

Abstract

In the present study, biochars from rice husk were synthesized via pyrolysis at 400, 550, 700 and 850 °C for 1 h under a limited O₂ atmosphere, characterized with a various techniques of and used as catalysts to activate persulfate and to [...] Read more.

In the present study, biochars from rice husk were synthesized via pyrolysis at 400, 550, 700 and 850 °C for 1 h under a limited O₂ atmosphere, characterized with a various techniques of and used as catalysts to activate persulfate and to degrade sulfamethoxazole (SMX). After physicochemical characterization of biochars. SMX degradation tests were performed using different water matrices, persulfate biochar and SMX concentrations and different initial pH solutions. Also, spiked solutions with bicarbonate, chloride, calcium nitrate, humic acid or alcohols were tested. It was found that catalytic reactivity rises with the pyrolysis temperature. Biochar is crucial for the oxidation of SMX and it can be described with a pseudo first–order kinetic model. Real matrices hinder the oxidation process, in waste water the SMX removal is 41% in 90 min, comparable with the inhibition obtained with spiked with bicarbonates solution (52% removal within 90 min) while complete removal can be achieved in ultrapure water matrices. The presence of alcohol slightly inhibits degradation contrary to the addition of sodium azide which causes significant inhibition, this is an evidence that degradation either under electron transfer/singlet oxygen control or dominated by surface-bound radicals. Full article

(This article belongs to the Special Issue Advances in the Application of Biochar in Catalytic Processes)

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17 pages, 3159 KiB

Open AccessArticle

Catalytic Hydrothermal Liquefaction of Penicillin Residue for the Production of Bio-Oil over Different Homogeneous/Heterogeneous Catalysts

by Chen Hong, Zhiqiang Wang, Yanxiao Si, Yi Xing, Jian Yang, Lihui Feng, Yijie Wang, Jiashuo Hu, Zaixing Li and Yifei Li

Catalysts 2021, 11(7), 849; https://doi.org/10.3390/catal11070849 - 15 Jul 2021

Cited by 12 | Viewed by 2621

Abstract

In this study, penicillin residue (PR) was used to prepare bio-oil by hydrothermal liquefaction. The effects of homogeneous (organic acid and alkaline catalysts) and heterogeneous catalysts (zeolite molecular sieve) on the yield and properties of bio-oil were investigated. The results show that there [...] Read more.

In this study, penicillin residue (PR) was used to prepare bio-oil by hydrothermal liquefaction. The effects of homogeneous (organic acid and alkaline catalysts) and heterogeneous catalysts (zeolite molecular sieve) on the yield and properties of bio-oil were investigated. The results show that there are significant differences in the catalytic performance of the catalysts. The effect of homogeneous catalysts on the bio-oil yield was not significant, which only increased from 26.09 (no catalysts) to 31.44 wt.% (Na₂CO₃, 8 wt.%). In contrast, heterogeneous catalysts had a more obvious effect, and the oil yield reached 36.44 wt.% after adding 5 wt.% MCM-48. Increasing the amount of catalyst enhanced the yield of bio-oil, but excessive amounts of catalyst led to a secondary cracking reaction, resulting in a reduction in bio-oil. Catalytic hydrothermal liquefaction reduced the contents of heteroatoms (oxygen, mainly), slightly increased the contents of C and H in the bio-oil and increased the higher heating value (HHV) and energy recovery (ER) of bio-oil. FTIR and GC-MS analyses showed that the addition of catalysts was beneficial in increasing hydrocarbons and oxygen-containing hydrocarbons in bio-oil and reducing the proportion of nitrogen-containing substances. Comprehensive analyses of the distribution of aromatic, nitrogen-containing and oxygen-containing components in bio-oil were also performed. This work is beneficial for further research on the preparation of bio-oil by hydrothermal liquefaction of antibiotic fermentation residue. Full article

(This article belongs to the Section Biomass Catalysis)

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10 pages, 2956 KiB

Open AccessFeature PaperArticle

Development of Visible-Light-Driven Rh–TiO₂–CeO₂ Hybrid Photocatalysts for Hydrogen Production

by Jong-Wook Hong

Catalysts 2021, 11(7), 848; https://doi.org/10.3390/catal11070848 - 15 Jul 2021

Cited by 10 | Viewed by 3002

Abstract

Visible-light-driven hydrogen production through photocatalysis has attracted enormous interest owing to its great potential to address energy and environmental issues. However, photocatalysis possesses several limitations to overcome for practical applications, such as low light absorption efficiency, rapid charge recombination, and poor stability of [...] Read more.

Visible-light-driven hydrogen production through photocatalysis has attracted enormous interest owing to its great potential to address energy and environmental issues. However, photocatalysis possesses several limitations to overcome for practical applications, such as low light absorption efficiency, rapid charge recombination, and poor stability of photocatalysts. Here, the preparation of efficient noble metal–semiconductor hybrid photocatalysts for photocatalytic hydrogen production is presented. The prepared ternary Rh–TiO₂–CeO₂ hybrid photocatalysts exhibited excellent photocatalytic performance toward the hydrogen production reaction compared with their counterparts, ascribed to the synergistic combination of Rh, TiO₂, and CeO₂. Full article

(This article belongs to the Special Issue Photo(electro)catalytic Reactions Combined with Ozone Oxidation Technique)

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17 pages, 3495 KiB

Open AccessReview

Epoxidation of Terpenes

by Yacoub Mahamat Ahmat, Sara Madadi, Luc Charbonneau and Serge Kaliaguine

Catalysts 2021, 11(7), 847; https://doi.org/10.3390/catal11070847 - 14 Jul 2021

Cited by 27 | Viewed by 6493

Abstract

Terpene epoxides are considered as potential primary intermediates in the synthesis of numerous green polymers including epoxy resins, polycarbonates, nonisocyanate polyurethanes and even some polyamides. In this chapter we describe recent efforts from our group to develop catalytic and noncatalytic processes for terpene [...] Read more.

Terpene epoxides are considered as potential primary intermediates in the synthesis of numerous green polymers including epoxy resins, polycarbonates, nonisocyanate polyurethanes and even some polyamides. In this chapter we describe recent efforts from our group to develop catalytic and noncatalytic processes for terpene epoxidation using a variety of oxidizing agents and process intensification methods. Most experimental tests deal with limonene epoxidation with applicability to some other terpenes also demonstrated. Full article

(This article belongs to the Special Issue Catalytic Epoxidation Reaction)

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15 pages, 9406 KiB

Open AccessFeature PaperArticle

Effect of Temperature, Syngas Space Velocity and Catalyst Stability of Co-Mn/CNT Bimetallic Catalyst on Fischer Tropsch Synthesis Performance

by Omid Akbarzadeh, Solhe F. Alshahateet, Noor Asmawati Mohd Zabidi, Seyedehmaryam Moosavi, Amir Kordijazi, Arman Amani Babadi, Nor Aliya Hamizi, Yasmin Abdul Wahab, Zaira Zaman Chowdhury and Suresh Sagadevan

Catalysts 2021, 11(7), 846; https://doi.org/10.3390/catal11070846 - 14 Jul 2021

Cited by 7 | Viewed by 5083

Abstract

The effect of reaction temperature, syngas space velocity, and catalyst stability on Fischer-Tropsch reaction was investigated using a fixed-bed microreactor. Cobalt and Manganese bimetallic catalysts on carbon nanotubes (CNT) support (Co-Mn/CNT) were synthesized via the strong electrostatic adsorption (SEA) method. For testing the [...] Read more.

The effect of reaction temperature, syngas space velocity, and catalyst stability on Fischer-Tropsch reaction was investigated using a fixed-bed microreactor. Cobalt and Manganese bimetallic catalysts on carbon nanotubes (CNT) support (Co-Mn/CNT) were synthesized via the strong electrostatic adsorption (SEA) method. For testing the performance of the catalyst, Co-Mn/CNT catalysts with four different manganese percentages (0, 5, 10, 15, and 20%) were synthesized. Synthesized catalysts were then analyzed by TEM, FESEM, atomic absorption spectrometry (AAS), and zeta potential sizer. In this study, the temperature was varied from 200 to 280 °C and syngas space velocity was varied from 0.5 to 4.5 L/g.h. Results showed an increasing reaction temperature from 200 °C to 280 °C with reaction pressure of 20 atm, the Space velocity of 2.5 L/h.g and H₂/CO ratio of 2, lead to the rise of CO % conversion from 59.5% to 88.2% and an increase for C₅₊ selectivity from 83.2% to 85.8%. When compared to the other catalyst formulation, the catalyst sample with 95% cobalt and 5% manganese on CNT support (95Co5Mn/CNT) performed more stable for 48 h on stream. Full article

(This article belongs to the Special Issue Current Advanced Technologies in Catalysts/Catalyzed Reactions)

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18 pages, 3288 KiB

Open AccessArticle

Adsorption Followed by Plasma Assisted Catalytic Conversion of Toluene into CO₂ on Hopcalite in an Air Stream

by Shilpa Sonar, Jean-Marc Giraudon, Savita Kaliya Perumal Veerapandian, Jean-François Lamonier, Rino Morent, Axel Löfberg and Nathalie De Geyter

Catalysts 2021, 11(7), 845; https://doi.org/10.3390/catal11070845 - 14 Jul 2021

Cited by 5 | Viewed by 2902

Abstract

The abatement of toluene was studied in a sequential adsorption-plasma catalysis (APC) process. Within this process, Hopcalite was used as bifunctional material: as adsorbent (storage stage) and as catalyst via the oxidation of adsorbed toluene (discharge stage). It was observed that the desorption [...] Read more.

The abatement of toluene was studied in a sequential adsorption-plasma catalysis (APC) process. Within this process, Hopcalite was used as bifunctional material: as adsorbent (storage stage) and as catalyst via the oxidation of adsorbed toluene (discharge stage). It was observed that the desorption and oxidation activity of the adsorbed toluene was significantly affected the process variables. In addition, the adsorption time influenced the CO₂ selectivity and CO₂ yield by changing the interaction between the catalyst and the plasma generated species. At least four APC sequences were performed for each examined condition suggesting that Hopcalite is very stable under plasma exposure during all the sequences. Consequently, these results could contribute to advance the plasma–catalyst system with an optimal VOC oxidation efficiency. The catalytic activity, amount of toluene adsorbed, amount of toluene desorbed and product formation have been quantified by FT-IR. Moreover, the catalyst was characterized by XRD, H₂-TPR, N₂ adsorption–desorption analysis and XPS. Hopcalite shows a good CO₂ selectivity and CO₂ yield when the APC process is performed with an adsorption time of 20 min and a plasma treatment with a discharge power of 46 W which leads to a low energy cost of 11.6 kWh·m⁻³ and energy yields of toluene and CO₂ of 0.18 (±0.01) g·kWh⁻¹ and 0.48 (±0.06) g·kWh⁻¹ respectively. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Environmental Catalysis—Contributions for a More Sustainable Society)

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7 pages, 2058 KiB

Open AccessArticle

3D Co-Ni-C Network from Milk as Competitive Bifunctional Catalysts for Methanol and Urea Electrochemical Oxidation

by Dana Ao, Yue Shi, Shuyuan Li, Ying Chang, Aiju Xu, Jingchun Jia and Meilin Jia

Catalysts 2021, 11(7), 844; https://doi.org/10.3390/catal11070844 - 14 Jul 2021

Cited by 5 | Viewed by 2555

Abstract

Methanol oxidation (MOR) and urea oxidation (UOR) have been considered for new types of fuel cells, but the lack of highly active nonnoble metal catalysts restricts such cells. A NiCo-modified biomass carbon (milk as the carbon source)-based catalyst with a 3D structure is [...] Read more.

Methanol oxidation (MOR) and urea oxidation (UOR) have been considered for new types of fuel cells, but the lack of highly active nonnoble metal catalysts restricts such cells. A NiCo-modified biomass carbon (milk as the carbon source)-based catalyst with a 3D structure is synthesized by using salt templates. The results show that 3D-C-NiCo (1:1) exhibits excellent MOR and UOR properties with a potential of 1.33 V vs. RHE and 1.35 V vs. RHE at 10 mA cm⁻², respectively. MOR and UOR reactions not only can replace the oxygen evolution reaction (OER) in consumption of electrolytic water but also can effectively degrade wastewater pollution rich in methanol and urea. Full article

(This article belongs to the Section Electrocatalysis)

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27 pages, 9528 KiB

Open AccessArticle

Effect of Textural Properties and Presence of Co-Cation on NH₃-SCR Activity of Cu-Exchanged ZSM-5

by Magdalena Jabłońska, Kinga Góra-Marek, Miha Grilc, Paolo Cleto Bruzzese, David Poppitz, Kamila Pyra, Michael Liebau, Andreas Pöppl, Blaž Likozar and Roger Gläser

Catalysts 2021, 11(7), 843; https://doi.org/10.3390/catal11070843 - 13 Jul 2021

Cited by 18 | Viewed by 4370

Abstract

Comparative studies over micro-/mesoporous Cu-containing zeolites ZSM-5 prepared by top-down treatment involving NaOH, TPAOH or mixture of NaOH/TPAOH (tetrapropylammonium hydroxide) were conducted. The results of the catalytic data revealed the highest activity of the Cu-ZSM-5 catalyst both in the absence and presence of [...] Read more.

Comparative studies over micro-/mesoporous Cu-containing zeolites ZSM-5 prepared by top-down treatment involving NaOH, TPAOH or mixture of NaOH/TPAOH (tetrapropylammonium hydroxide) were conducted. The results of the catalytic data revealed the highest activity of the Cu-ZSM-5 catalyst both in the absence and presence of water vapor. The physico-chemical characterization (diffuse reflectance UV-Vis (DR UV-Vis), Fourier transform infrared (FT-IR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, temperature-programmed desorption of NO_x (TPD-NO_x), and microkinetic modeling) results indicated that the microporous structure of ZSM-5 effectively stabilized isolated Cu ion monomers. Besides the attempts targeted to the modification of the textural properties of the parent ZSM-5, in the next approach, we studied the effect of the co-presence of sodium and copper cations in the microporous H-ZSM-5. The presence of co-cation promoted the evolution of [Cu–O–Cu]²⁺ dimers that bind NO_x strongly with the desorption energy barrier of least 80 kJ mol⁻¹. Water presence in the gas phase significantly decreases the rate of ammonia oxidation, while the reaction rates and activation energies of NH₃-SCR remain unaffected. Full article

(This article belongs to the Special Issue Structured Materials for Catalytic Applications)

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31 pages, 7358 KiB

Open AccessArticle

Comparison of Support Effects on Phillips and Metallocene Catalysts

by Qing Yang and Max Paul McDaniel

Catalysts 2021, 11(7), 842; https://doi.org/10.3390/catal11070842 - 13 Jul 2021

Cited by 11 | Viewed by 4992

Abstract

Both metallocene and Phillips chromium catalysts are used in the commercial manufacture of polyethylene. Unlike most other commercial metallocene systems, the Chevron Phillips Chemical (CPC) platform does not use methylaluminoxane or fluoroorganic boranes. Instead, the support itself serves to activate (ionize) the metallocenes, [...] Read more.

Both metallocene and Phillips chromium catalysts are used in the commercial manufacture of polyethylene. Unlike most other commercial metallocene systems, the Chevron Phillips Chemical (CPC) platform does not use methylaluminoxane or fluoroorganic boranes. Instead, the support itself serves to activate (ionize) the metallocenes, which then polymerize ethylene at high activity. Most of these solid acid supports can also be used to anchor Cr to make a Phillips catalyst. This provides an interesting opportunity to compare the polymerization responses by these two disparate systems, Phillips Cr and CPC metallocene, when supported on the same solid acid carriers. In this study, both chromium oxide and several metallocenes were deposited onto a variety of solid oxides, under a variety of conditions, and the resulting support effects were observed and compared. Although using seemingly different chemistries, the two catalyst systems exhibited a surprising number of similarities, which can be attributed to the acidity and porosity of these diverse supports. Full article

(This article belongs to the Special Issue New Trends in Phillips and Other Catalysts for Ethylene Polymerization)

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14 pages, 1563 KiB

Open AccessArticle

Elucidating Synergistic Effects of Different Metal Ratios in Bimetallic Fe/Co-N-C Catalysts for Oxygen Reduction Reaction

by Marius Gollasch, Julia Müller-Hülstede, Henrike Schmies, Dana Schonvogel, Peter Wagner, Alexander Dyck and Michael Wark

Catalysts 2021, 11(7), 841; https://doi.org/10.3390/catal11070841 - 13 Jul 2021

Cited by 13 | Viewed by 3161

Abstract

Lowering or eliminating the noble-metal content in oxygen reduction fuel cell catalysts could propel the large-scale introduction of commercial fuel cell systems. Several noble-metal free catalysts are already under investigation with the metal-nitrogen-carbon (Me-N-C) system being one of the most promising. In this [...] Read more.

Lowering or eliminating the noble-metal content in oxygen reduction fuel cell catalysts could propel the large-scale introduction of commercial fuel cell systems. Several noble-metal free catalysts are already under investigation with the metal-nitrogen-carbon (Me-N-C) system being one of the most promising. In this study, a systematic approach to investigate the influence of metal ratios in bimetallic Me-N-C fuel cells oxygen reduction reaction (ORR) catalysts has been taken. Different catalysts with varying ratios of Fe and Co have been synthesized and characterized both physically and electrochemically in terms of activity, selectivity and stability with the addition of an accelerated stress test (AST). The catalysts show different electrochemical properties depending on the metal ratio such as a high electrochemical mass activity with increasing Fe ratio. Properties do not change linearly with the metal ratio, with a Fe/Co ratio of 5:3 showing a higher mass activity with simultaneous higher stability. Selectivity indicators plateau for catalysts with a Co content of 50% metal ratio and less, showing the same values as a monometallic Co catalyst. These findings indicate a deeper relationship between the ratio of different metals and physical and electrochemical properties in bimetallic Me-N-C catalysts. Full article

(This article belongs to the Section Electrocatalysis)

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