Catalysts

8 pages, 20230 KiB

Open AccessArticle

Ion Composition of the Beam Plasma Generated by Electron-Beam Evaporation of Metals and Ceramic in the Forevacuum Range of Pressure

by Andrey V. Tyunkov, Efim M. Oks, Yury G. Yushkov and Denis B. Zolotukhin

Catalysts 2022, 12(5), 574; https://doi.org/10.3390/catal12050574 - 23 May 2022

Cited by 6 | Viewed by 2106

Abstract

We present the results of measurements of the ion composition of the plasma generated by an accelerated electron beam in the forevacuum pressure range. It has been found that the main contribution to ionization processes comes from beam electrons. It has been shown [...] Read more.

We present the results of measurements of the ion composition of the plasma generated by an accelerated electron beam in the forevacuum pressure range. It has been found that the main contribution to ionization processes comes from beam electrons. It has been shown that, during the electron-beam evaporation of metal or ceramic targets, the number of ions evaporated from the materials in the beam plasma significantly exceeds the number of ions produced from the residual atmosphere and admitted gases. Together, electron beams and beam-produced plasma can catalyze the processes of coatings deposition or modification of the surface layer of the samples. Full article

(This article belongs to the Special Issue Plasma Catalyzed Industrial and Biomedical Chemistry: Pathways and Applications)

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28 pages, 6085 KiB

Open AccessReview

Recent Advances in Carbon-Silica Composites: Preparation, Properties, and Applications

by Tianhao Wu, Quanli Ke, Mei Lu, Pengyun Pan, Ying Zhou, Zhenyu Gu, Guokai Cui and Hanfeng Lu

Catalysts 2022, 12(5), 573; https://doi.org/10.3390/catal12050573 - 23 May 2022

Cited by 20 | Viewed by 7199

Abstract

The thermal catalytic conversion of biomass is currently a prevalent method for producing activated carbon with superb textural properties and excellent adsorption performance. However, activated carbon suffers severely from its poor thermal stability, which can easily result in spontaneous burning. In contrast, silica [...] Read more.

The thermal catalytic conversion of biomass is currently a prevalent method for producing activated carbon with superb textural properties and excellent adsorption performance. However, activated carbon suffers severely from its poor thermal stability, which can easily result in spontaneous burning. In contrast, silica material is famed for its easy accessibility, high specific surface area, and remarkable thermal stability; however, its broader applications are restricted by its strong hydrophilicity. Based on this, the present review summarizes the recent progress made in carbon-silica composite materials, including the various preparation methods using diverse carbon (including biomass resources) and silica precursors, their corresponding structure–function relationship, and their applications in adsorption, insulation, batteries, and sensors. Through their combination, the drawbacks of the individual materials are circumvented while their original advantages are maintained. Finally, several bottlenecks existing in the field of carbon-silica composites, from synthesis to applications, are discussed in this paper, and possible solutions are given accordingly. Full article

(This article belongs to the Special Issue Catalytic Conversion of Cellulose and Lignin)

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13 pages, 3244 KiB

Open AccessArticle

Fabrication of 5 V High-Performance Solid-State Asymmetric Supercapacitor Device Based on MnO₂/Graphene/Ni Electrodes

by Ming-Chun Hsieh, Bo-Han Chen, Zhong-Yun Hong, Jue-Kai Liu, Pin-Cheng Huang and Chao-Ming Huang

Catalysts 2022, 12(5), 572; https://doi.org/10.3390/catal12050572 - 23 May 2022

Cited by 12 | Viewed by 2701

Abstract

To reach high energy density and excellent cycle stability, an asymmetric supercapacitor device combining a high-power electric double-layer capacitor (EDLC) anode and high energy density battery-type cathode has been designed and fabricated. A binder-free strategy was used to prepare cathode by coating graphene [...] Read more.

To reach high energy density and excellent cycle stability, an asymmetric supercapacitor device combining a high-power electric double-layer capacitor (EDLC) anode and high energy density battery-type cathode has been designed and fabricated. A binder-free strategy was used to prepare cathode by coating graphene (G) on Ni foam (Ni), then electrodepositing MnO₂, followed by calcination process. The potentiodynamic (PD) electrodeposition cycles of MnO₂ onto graphene significantly impact the electrochemical properties. Benefiting from the hierarchical structure and binder-free process of the designed 75 C/G/Ni hybrid cathode, potentiostatic (PS) electrodeposition followed by PD electrodeposition for 75 cycles demonstrates a high specific capacitance of 691 F g⁻¹ at 2 A g⁻¹. The enhanced capacitive performance can be attributed to the synergistic effect between MnO₂ nanosheets and graphene, in which graphene can serve as ideal support matrix and conductive channels. Furthermore, an asymmetric supercapacitor was fabricated with 75 C/G/Ni and (G + AC)/Ni as the cathode and anode, respectively, and a carboxymethyl cellulose–potassium hydroxide (CMC-KOH) gel electrolyte. The 75 C/G/Ni//(G + AC)/Ni asymmetric supercapacitor (ASC) exhibits a maximum energy density of 43 kW kg⁻¹ at a power density of 302 W kg⁻¹ with a potential window of 1.6 V and maintains good cycling stability of 88% capacitance retention at 2 A g⁻¹ (over 5000 cycles). Four solid-state asymmetric supercapacitors stack connected in series display an effective 5.0 V working potential to increase the voltage and output energy as a device. The device was charged using a 18,650 Li battery with a voltage of +3.8 V for 30 s and discharged six white LEDs for 20 min. The facile fabrication and remarkable capacitive performance of the MnO₂/G/Ni hybrid make it a promising electrode candidate in electrochemical energy conversion/storage devices. Full article

(This article belongs to the Special Issue Synthesis and Photocatalytic Activity of Composite)

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10 pages, 3907 KiB

Open AccessArticle

Pt/C-TiO₂ as Oxygen Reduction Electrocatalysts against Sulfur Poisoning

by Yuxin Liu, Jing Ye, Fanpeng Kong, Chunyu Du, Pengjian Zuo, Lei Du and Geping Yin

Catalysts 2022, 12(5), 571; https://doi.org/10.3390/catal12050571 - 23 May 2022

Cited by 5 | Viewed by 2559

Abstract

Proton exchange membrane (PEM) fuel cells using Pt-based materials as electrocatalysts have achieved a decent performance, represented by the launched Toyota Mirai vehicle. The ideal PEM fuel cells consume stored pure hydrogen and air. However, SO₂, as a primary air contaminant, [...] Read more.

Proton exchange membrane (PEM) fuel cells using Pt-based materials as electrocatalysts have achieved a decent performance, represented by the launched Toyota Mirai vehicle. The ideal PEM fuel cells consume stored pure hydrogen and air. However, SO₂, as a primary air contaminant, may be fed along with air at the cathode, leading to Pt site deactivation. Therefore, it is important to improve the SO₂ tolerance of catalysts for the stability of the oxygen reduction reaction (ORR). In this work, we develop the Pt/C-TiO₂ catalyst against SO₂ poisoning during ORR. Impressively, the hybrid Pt/C-TiO₂ catalyst with 20 mass % TiO₂ shows the best ORR and anti-toxic performance: the kinetic current density of ORR is 20.5% higher and the degradation rate after poisoning is 50% lower than Pt/C. The interaction between Pt and TiO₂ as well as the abundant hydroxyl groups on the surface of TiO₂ are both revealed to account for the accelerated removal of poisonous SO₂ on Pt surfaces. Full article

(This article belongs to the Special Issue Efficient Oxygen Electrocatalysts for Zn-Air Battery)

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15 pages, 2069 KiB

Open AccessFeature PaperReview

Glycerol and Catalysis by Waste/Low-Cost Materials—A Review

by Ana Alice Farias da Costa, Alex de Nazaré de Oliveira, Roberto Esposito, Christophe Len, Rafael Luque, Renata Coelho Rodrigues Noronha, Geraldo Narciso da Rocha Filho and Luís Adriano Santos do Nascimento

Catalysts 2022, 12(5), 570; https://doi.org/10.3390/catal12050570 - 23 May 2022

Cited by 22 | Viewed by 3846 | Correction

Abstract

The growing global demand for renewable energy sources can be reached using biofuels such as biodiesel, for example. The most used route to produce biodiesel is the transesterification reaction of oils or fats with short-chain alcohols, generating fatty acid esters (biodiesel) and a [...] Read more.

The growing global demand for renewable energy sources can be reached using biofuels such as biodiesel, for example. The most used route to produce biodiesel is the transesterification reaction of oils or fats with short-chain alcohols, generating fatty acid esters (biodiesel) and a very important by-product, glycerol (Gly). Gly is widely used in different sectors of the industry, and in order to add value to this by-product, heterogeneous catalysis becomes a relevant tool, whether to transform glycerol into other chemical products of interest or even use it in the production of catalysts. Among the several studies found in the literature, the use of low-cost materials and/or wastes from the most diverse activities to prepare active catalytic materials for the transformation of Gly has been increasingly reported due to its valuable advantages, especially related to the cost of raw materials and environmental aspects. Thus, this brief review article presents the relationship between catalysis, low-cost materials, waste, and glycerol, through different studies that show glycerol being transformed through reactions catalyzed by materials produced from low-cost sources/waste or with the glycerol itself used as a catalyst. Full article

(This article belongs to the Special Issue Catalytic Valorization of Glycerol: Strategies and Perspectives)

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18 pages, 7549 KiB

Open AccessFeature PaperArticle

Mechanism Insight into Catalytic Performance of Ni₁₂P₅ over Ni₂P toward the Catalytic Deoxygenation of Butyric Acid

by Shuai Fu, Dan Li, Tinghao Liu, Lijuan Liu, Huaqing Yang and Changwei Hu

Catalysts 2022, 12(5), 569; https://doi.org/10.3390/catal12050569 - 21 May 2022

Cited by 1 | Viewed by 2097

Abstract

The Ni/P ratio of nickel phosphide has an important effect on the catalytic performance toward the deoxygenation of fatty acids to biofuel. The Ni₁₂P₅ cluster is preferred to model Ni₁₂P₅ catalyst with butyric acid as the reactant [...] Read more.

The Ni/P ratio of nickel phosphide has an important effect on the catalytic performance toward the deoxygenation of fatty acids to biofuel. The Ni₁₂P₅ cluster is preferred to model Ni₁₂P₅ catalyst with butyric acid as the reactant model of palmitic acid. The catalytic deoxygenation mechanism of butyric acid over Ni₁₂P₅ cluster has been theoretically investigated at GGA-PBE/DSPP, DNP level in dodecane solution. From butyric acid, the hydrodehydration is predominated to form n-butanal. Then, from n-butanal, low temperature benefits the hydroreduction to form butanol and then hydrodehydration to produce n-butane, whereas high temperature favors the direct decarbonylation to yield propane. n-Butane originates from n-butanol through hydrodehydration and not from n-butylene. Propane comes from n-butanal through decarbonylation and not from propanol and/or propylene. Additionally, CO stems from n-butanal through decarbonylation, whereas CO₂ is ruled out from butyric acid through decarboxylation. Compared with Ni₁₂P₆ cluster, Ni₁₂P₅ cluster exhibits higher catalytic activity for the formation of butanal, n-butanol, and n-butane, while it displays lower catalytic activity toward the direct decarbonylation and dehydration to yield propylene. These results can be attributed to less negative charges of Ni-sites over Ni₁₂P₅ cluster, compared with Ni₁₂P₆ cluster. Full article

(This article belongs to the Topic Catalysis for Sustainable Chemistry and Energy)

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11 pages, 2497 KiB

Open AccessArticle

Cobalt-Containing Nitrogen-Doped Carbon Materials Derived from Saccharides as Efficient Electrocatalysts for Oxygen Reduction Reaction

by Kaidi Veske, Ave Sarapuu, Maike Käärik, Arvo Kikas, Vambola Kisand, Helle-Mai Piirsoo, Alexey Treshchalov, Jaan Leis, Aile Tamm and Kaido Tammeveski

Catalysts 2022, 12(5), 568; https://doi.org/10.3390/catal12050568 - 20 May 2022

Cited by 6 | Viewed by 3322

Abstract

The development of non-precious metal electrocatalysts towards oxygen reduction reaction (ORR) is crucial for the commercialisation of polymer electrolyte fuel cells. In this work, cobalt-containing nitrogen-doped porous carbon materials were prepared by a pyrolysis of mixtures of saccharides, cobalt nitrate and dicyandiamide, which [...] Read more.

The development of non-precious metal electrocatalysts towards oxygen reduction reaction (ORR) is crucial for the commercialisation of polymer electrolyte fuel cells. In this work, cobalt-containing nitrogen-doped porous carbon materials were prepared by a pyrolysis of mixtures of saccharides, cobalt nitrate and dicyandiamide, which acts as a precursor for reactive carbon nitride template and a nitrogen source. The rotating disk electrode (RDE) experiments in 0.1 M KOH solution showed that the glucose-derived material with optimised cobalt content had excellent ORR activity, which was comparable to that of 20 wt% Pt/C catalyst. In addition, the catalyst exhibited high tolerance to methanol, good stability in short-time potential cycling test and low peroxide yield. The materials derived from xylan, xylose and cyclodextrin displayed similar activities, indicating that various saccharides can be used as inexpensive and sustainable precursors to synthesise active catalyst materials for anion exchange membrane fuel cells. Full article

(This article belongs to the Special Issue Heterogeneous Electrocatalysis: Fundamentals and Applications)

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13 pages, 3334 KiB

Open AccessArticle

Substrate Specificity of an Aminopropyltransferase and the Biosynthesis Pathway of Polyamines in the Hyperthermophilic Crenarchaeon Pyrobaculum calidifontis

by Wakao Fukuda, Mamoru Osaki, Yusuke Yasuda, Ryota Hidese, Tsunehiko Higuchi, Naoki Umezawa, Shinsuke Fujiwara and Eiichi Mizohata

Catalysts 2022, 12(5), 567; https://doi.org/10.3390/catal12050567 - 20 May 2022

Cited by 1 | Viewed by 2767

Abstract

The facultative anaerobic hyperthermophilic crenarchaeon Pyrobaculum calidifontis possesses norspermine (333), norspermidine (33), and spermidine (34) as intracellular polyamines (where the number in parentheses represents the number of methylene CH₂ chain units between NH₂, or [...] Read more.

The facultative anaerobic hyperthermophilic crenarchaeon Pyrobaculum calidifontis possesses norspermine (333), norspermidine (33), and spermidine (34) as intracellular polyamines (where the number in parentheses represents the number of methylene CH₂ chain units between NH₂, or NH). In this study, the polyamine biosynthesis pathway of P. calidifontis was predicted on the basis of the enzymatic properties and crystal structures of an aminopropyltransferase from P. calidifontis (Pc-SpeE). Pc-SpeE shared 75% amino acid identity with the thermospermine synthase from Pyrobaculum aerophilum, and recombinant Pc-SpeE could synthesize both thermospermine (334) and spermine (343) from spermidine and decarboxylated S-adenosyl methionine (dcSAM). Recombinant Pc-SpeE showed high enzymatic activity when aminopropylagmatine and norspermidine were used as substrates. By comparison, Pc-SpeE showed low affinity toward putrescine, and putrescine was not stably bound in its active site. Norspermidine was produced from thermospermine by oxidative degradation using a cell-free extract of P. calidifontis, whereas 1,3-diaminopropane (3) formation was not detected. These results suggest that thermospermine was mainly produced from arginine via agmatine, aminopropylagmatine, and spermidine. Norspermidine was produced from thermospermine by an unknown polyamine oxidase/dehydrogenase followed by norspermine formation by Pc-SpeE. Full article

(This article belongs to the Special Issue Biocatalysis and Biotransformation of Extremozymes)

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15 pages, 4740 KiB

Open AccessArticle

Selective Deoxygenation of Sludge Palm Oil into Diesel Range Fuel over Mn-Mo Supported on Activated Carbon Catalyst

by Abdulkareem Ghassan Alsultan, Nurul Asikin-Mijan, Laith K. Obeas, Aminul Islam, Nasar Mansir, Siow Hwa Teo, Siti Zulaika Razali, Maadh F. Nassar, Surahim Mohamad and Yun Hin Taufiq-Yap

Catalysts 2022, 12(5), 566; https://doi.org/10.3390/catal12050566 - 20 May 2022

Cited by 10 | Viewed by 2442

Abstract

Originating from deoxygenation (DO) technology, green diesel was innovated in order to act as a substitute for biodiesel, which contains unstable fatty acid alkyl ester owing to the existence of oxygenated species. Green diesel was manufactured following a process of catalytic DO of [...] Read more.

Originating from deoxygenation (DO) technology, green diesel was innovated in order to act as a substitute for biodiesel, which contains unstable fatty acid alkyl ester owing to the existence of oxygenated species. Green diesel was manufactured following a process of catalytic DO of sludge palm oil (SPO). An engineered Mn_(0.5%)-Mo_(0.5%)/AC catalyst was employed in a hydrogen-free atmosphere. The influence of Manganese (Mn) species (0.1–1 wt.%) on DO reactivity and the dissemination of the product were examined. The Mn_(0.5%)-Mo_(0.5%)/AC formulation gave rise to a superior harvest of approximately 89% liquid hydrocarbons; a higher proportion of diesel fraction selectivity n-(C₁₅+C₁₇) was obtained in the region of 93%. Where acid and basic active sites were present on the Mn_(0.5%)-Mo_(0.5%)/AC catalyst, decarboxylation and decarbonylation reaction mechanisms of SPO to DO were enhanced. Evidence of the high degree of stability of the Mn_(0.5%)-Mo_(0.5%)/AC catalyst during five continuous runs was presented, which, in mild reaction conditions, gave rise to a consistent hydrocarbon harvest of >72% and >94% selectivity for n-(C₁₅+C₁₇). Full article

(This article belongs to the Special Issue Conversion of Biomass and Biomass Derivatives with Zeolite-Based Catalysts)

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20 pages, 2360 KiB

Open AccessArticle

The Role of Nickel and Brønsted Sites on Ethylene Oligomerization with Ni-H-Beta Catalysts

by Gabriel V. S. Seufitelli, Jason J. W. Park, Phuong N. Tran, Anthony Dichiara, Fernando L. P. Resende and Rick Gustafson

Catalysts 2022, 12(5), 565; https://doi.org/10.3390/catal12050565 - 20 May 2022

Cited by 5 | Viewed by 2590

Abstract

The present work studies the adsorption of ethylene on Ni-H-Beta particles to unravel the roles of nickel and Brønsted sites in the catalytic oligomerization of ethylene. Three models (i.e., two based on the Cossee–Arlman mechanism and one based on the metallacycle mechanism) are [...] Read more.

The present work studies the adsorption of ethylene on Ni-H-Beta particles to unravel the roles of nickel and Brønsted sites in the catalytic oligomerization of ethylene. Three models (i.e., two based on the Cossee–Arlman mechanism and one based on the metallacycle mechanism) are examined in terms of the nature of the active sites and the adsorption mechanism involved in the ethylene coordination step. The results are consistent with the participation of two active sites in the formation of [Ni(II)-H]⁺ Cossee–Arlman centers and also suggest that ethylene dissociates upon adsorption on [Ni(II)-H]⁺ sites. Further characterization of Ni-H-Beta catalysts prepared at different nickel loadings and silica-to-alumina ratios reveals that highly dispersed Ni²⁺ exists on the catalyst surface and interacts with the catalyst’s lattice oxygen and free NiO crystals. At the same time, the kinetic results indicate that Brønsted sites may form isolated nickel-hydride ([Ni(II)-H]⁺) centers on the catalyst surface. In addition, the presence of residual, noncoordinated Ni²⁺ and Brønsted sites (not involved in the formation of [Ni(II)-H]⁺ sites) shows a reduced probability of the formation of nickel-hydride sites, hindering the conversion rate of ethylene. A mechanism for forming [Ni(II)-H]⁺ centers is proposed, involving ethylene adsorption over Ni²⁺ and a Brønsted site. This research has important implications for improving ethylene oligomerization processes over nickel-based heterogeneous catalysts. Full article

(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)

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12 pages, 2192 KiB

Open AccessArticle

Visible Light-Induced Photocatalyst with Au/TiO₂ Nanocomposites Fabricated through Pulsed Laser-Induced Photolysis

by Bing-Yen Wang, Ya-Shing Hsiao, Pei-Ching Wei, Yuan-Tung Liu, Chih-Chien Chu and Vincent K. S. Hsiao

Catalysts 2022, 12(5), 564; https://doi.org/10.3390/catal12050564 - 20 May 2022

Cited by 8 | Viewed by 2522

Abstract

Gold–titanium oxide nanocomposites (Au–TiO₂ NCPs) were fabricated through pulsed laser-induced photolysis (PIPS) and verified to be usable for the visible light catalytic degradation of methylene blue (MB). The PIPS method can produce a sufficient amount of NCPs quickly and has potential to [...] Read more.

Gold–titanium oxide nanocomposites (Au–TiO₂ NCPs) were fabricated through pulsed laser-induced photolysis (PIPS) and verified to be usable for the visible light catalytic degradation of methylene blue (MB). The PIPS method can produce a sufficient amount of NCPs quickly and has potential to be commercialized. In contrast to other studies, we clarified the optical spectrum of the light sources, including peak power, bandwidth, and total intensity used for photodegradation reactions and discovered that the photodegradation efficiency of the produced Au–TiO₂ NCPs in the wavelength range of 405 nm could reach 37% in 30 min due to the charge transfer between Au and TiO₂. The control experiment shows that the addition of individual Au and TiO₂ nanoparticles (NPs) to an MB solution has no enhancement of degradation ability under visible light illumination. The photodegradation of Au–TiO₂ NCPs can be further improved by increasing the concentrations of auric acid and TiO₂ NPs in a precursor under PIPS fabrication. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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18 pages, 7326 KiB

Open AccessReview

Recent Achievements in the Synthesis of Cyclic Carbonates from Olefins and CO₂: The Rational Design of the Homogeneous and Heterogeneous Catalytic System

by Ting Yan, Zixian Wang, Li Guo, Ran Zhang, Haijuan Zhan, Jialing Chen and Xiaoqin Wu

Catalysts 2022, 12(5), 563; https://doi.org/10.3390/catal12050563 - 20 May 2022

Cited by 4 | Viewed by 3169

Abstract

With the consumption of fossil fuels, the level of CO₂ in the atmosphere is growing rapidly, which leads to global warming. Hence, the chemical conversion of CO₂ into high value-added products is one of the most important approaches to reducing CO [...] Read more.

With the consumption of fossil fuels, the level of CO₂ in the atmosphere is growing rapidly, which leads to global warming. Hence, the chemical conversion of CO₂ into high value-added products is one of the most important approaches to reducing CO₂ emissions. Due to being simple, inexpensive and environmentally friendly, the direct synthesis of cyclic carbonates from olefins and CO₂ is a promising project for industrial application. In this review, we discuss the design of the homogeneous and heterogeneous catalytic system for the synthesis of cyclic carbonates from the reaction of olefins and CO₂. Usually, the catalyst contains the epoxidation active site and the cycloaddition active site, which could achieve the oxidation of oleifins and the CO₂-insert, respectively. This review will provide a comprehensive overview of the direct synthesis of cyclic carbonates from olefins and CO₂ catalyzed by homogeneous and heterogeneous catalysts. The focus mainly lies on the rational fabrication of multifunctional catalysts, and provides a new perspective for the design of catalysts. Full article

(This article belongs to the Topic Catalysis: Homogeneous and Heterogeneous)

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29 pages, 8659 KiB

Open AccessArticle

Preparation and Characterization of Supported Molybdenum Doped TiO₂ on α-Al₂O₃ Ceramic Substrate for the Photocatalytic Degradation of Ibuprofen (IBU) under UV Irradiation

by Chukwuka Bethel Anucha, Emin Bacaksiz, Vassilis N. Stathopoulos, Pavlos K. Pandis, Christos Argirusis, Constantina-Dia Andreouli, Zoi Tatoudi and Ilknur Altin

Catalysts 2022, 12(5), 562; https://doi.org/10.3390/catal12050562 - 19 May 2022

Cited by 7 | Viewed by 2557

Abstract

TiO₂-based photocatalyst materials have been widely studied for the abatement of contaminants of emerging concerns (CECs) in water sources. In this study, 1.5 wt% Mo-doped HRTiO₂ was obtained by the sonochemical method. The material was analyzed and characterized for thermal, [...] Read more.

TiO₂-based photocatalyst materials have been widely studied for the abatement of contaminants of emerging concerns (CECs) in water sources. In this study, 1.5 wt% Mo-doped HRTiO₂ was obtained by the sonochemical method. The material was analyzed and characterized for thermal, structural/textural, morphological, and optical properties using TGA-DSC, XRD, TEM, FTIR, XPS, SEM-EDS, BET (N₂ adsorption-desorption measurement and BJH application method), and UV-Vis/DRS measurement. By the dip-coating technique, ~5 mg of Mo/HRTiO₂ as an active topcoat was deposited on ceramic. In suspension and for photocatalyst activity performance evaluation, 1 g/L of 1.5 wt% (Mo)/HRTiO₂ degraded ~98% of initial 50 mg/L IBU concentration after 80 min of 365 nm UV light irradiation and under natural (unmodified) pH conditions. Effects of initial pH condition, catalyst dosage, and initial pollutant concentration were also investigated in the photocatalyst activity performance in suspension. The photocatalyst test on the supported catalyst removed ~60% of initial 5mg/L IBU concentration, while showing an improved performance with ~90% IBU removal employing double and triple numbers of coated disk tablets. After three successive cycle test runs, XRD phase reflections of base TiO₂ component of the active photocatalyst supported layer remained unchanged: An indication of surface coat stability after 360 min of exposure under 365 nm UV irradiation. Full article

(This article belongs to the Special Issue Photocatalytic Activity of TiO₂ and Its Applications)

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13 pages, 4600 KiB

Open AccessArticle

Study of Intermolecular Interaction between Small Molecules and Carbon Nanobelt: Electrostatic, Exchange, Dispersive and Inductive Forces

by Chen Lu, Panpan Chen, Cunlei Li and Jingang Wang

Catalysts 2022, 12(5), 561; https://doi.org/10.3390/catal12050561 - 19 May 2022

Cited by 5 | Viewed by 2538

Abstract

The conjugated structure of carbon is used in chemical sensing and small molecule catalysis because of its high charge transfer ability, and the interaction between carbon materials and small molecules is the main factor determining the performance of sensing and catalytic reactions. In [...] Read more.

The conjugated structure of carbon is used in chemical sensing and small molecule catalysis because of its high charge transfer ability, and the interaction between carbon materials and small molecules is the main factor determining the performance of sensing and catalytic reactions. In this work, Reduced Density Gradient (RDG) and Symmetry-Adapted Perturbation Theory (SAPT) energy decomposition methods were used in combination to investigate the heterogeneity of catalytic substrates commonly used in energy chemistry with [6, 6] the carbon nanobelt ([6, 6] CNB, the interaction properties and mechanisms inside and outside the system). The results show that most of the attractive forces between dimers are provided by dispersive interactions, but electrostatic interactions cannot be ignored either. The total energy of the internal adsorption of [6, 6] CNB was significantly smaller than that of external adsorption, which led to the small molecules being more inclined to adsorb in the inner region of [6, 6] CNB. The dispersive interactions of small molecules adsorbed on [6, 6] CNB were also found to be very high. Furthermore, the dispersive interactions of the same small molecules adsorbed inside [6, 6] CNB were significantly stronger than those adsorbed outside. In [6, 6] CNB dimers, dispersion played a major role in the mutual attraction of molecules, accounting for 70% of the total attraction. Full article

(This article belongs to the Special Issue Functional Materials for Application in Adsorption & Catalysis)

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17 pages, 9347 KiB

Open AccessFeature PaperArticle

Unraveling the Reaction Mechanism of HCHO Catalytic Oxidation on Pristine Co₃O₄ (110) Surface: A Theoretical Study

by Rong Li, Tingting Huang, Yu Huang, Meijuan Chen, Shun-cheng Lee, Wingkei Ho and Junji Cao

Catalysts 2022, 12(5), 560; https://doi.org/10.3390/catal12050560 - 19 May 2022

Cited by 6 | Viewed by 2600

Abstract

Various reaction mechanisms for the catalytic degradation of formaldehyde (HCHO) remain to be debated. Density functional theory (DFT) was applied to investigate whether the catalytic oxidation of HCHO on pristine Co₃O₄ (110) surface follows the Mars-van Krevelen (MvK) mechanism or [...] Read more.

Various reaction mechanisms for the catalytic degradation of formaldehyde (HCHO) remain to be debated. Density functional theory (DFT) was applied to investigate whether the catalytic oxidation of HCHO on pristine Co₃O₄ (110) surface follows the Mars-van Krevelen (MvK) mechanism or the Langmuir–Hinshelwood (L-H) mechanism. Firstly, HCHO and O₂ co-adsorb on the surface and two H atoms from HCHO are peculiarly prone to transfer to O₂, forming CO and HOOH. For the MvK mechanism, CO₂ is generated through CO grabbing a lattice oxygen. Meanwhile, the O–O bond of HOOH is broken into two OH groups. One OH fills the oxygen vacancy and its H atom moves to another OH group for H₂O formation. For the L-H mechanism, CO directly obtains one OH group to generate COOH. Subsequently, the H atom of COOH transfers to another OH group along with CO₂ and H₂O generation. Both two mechanisms exhibit a similar maximum activation barrier. The lattice oxygen in the MvK mechanism and the surface-absorbed OH group in the L-H mechanism are the key reactive oxygen species. The small difference in energetic span further suggests that the catalytic cycle through the two mechanisms is feasible. This theoretical study provides new insight into the catalytic reaction path of HCHO oxidation on pristine Co₃O₄ surface. Full article

(This article belongs to the Special Issue Environmental Catalysis for Air Pollution Applications)

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13 pages, 2072 KiB

Open AccessFeature PaperArticle

Yttria-Stabilized Zirconia of Balanced Acid-Base Pair for Selective Dehydration of 4-Methyl-2-pentanol to 4-Methyl-1-pentene

by Jae-Hong Lee, Minseok Kim, Suhyun Lim, Dinesh Kumar Mishra and Young-Woong Suh

Catalysts 2022, 12(5), 559; https://doi.org/10.3390/catal12050559 - 19 May 2022

Cited by 5 | Viewed by 3049

Abstract

The selective transformation of secondary alcohols to alpha-olefins is a challenging task in heterogeneous catalysis, as is the case of 4-methyl-2-pentanol (4M2Pol) conversion to 4-methyl-1-pentene (4M1P). Herein, the co-precipitated yttria-stabilized zirconia (YSZ) catalysts exhibit superior performance to both bare and Y-impregnated ZrO₂ [...] Read more.

The selective transformation of secondary alcohols to alpha-olefins is a challenging task in heterogeneous catalysis, as is the case of 4-methyl-2-pentanol (4M2Pol) conversion to 4-methyl-1-pentene (4M1P). Herein, the co-precipitated yttria-stabilized zirconia (YSZ) catalysts exhibit superior performance to both bare and Y-impregnated ZrO₂ in selective 4M2Pol dehydration. In order to track the activity origin of YSZ, temperature-programmed desorption experiments using NH₃ and CO₂ are performed along with X-ray photoelectron spectroscopy. The conversion of 4M2Pol (max. 85%) is proportional to weak acidity and inverse to medium basicity. In contrast, the selectivity of 4M1P increases to 80% as the ratio of weak acidity to medium basicity is close to and exceeds the unity. These indications corroborate that the balanced acid–base pair of YSZ leads to the selective formation of 4M1P from 4M2Pol, which is caused by strong interaction between zirconia and yttria in the YSZ. Additionally, the dehydration activity over YSZ of 4 mol% yttrium is sustained at 450 °C for 50 h. Therefore, the YSZ, which is often used for electrocatalysis, is believed to be a promising catalyst in the dehydration of 4M2Pol and, further, secondary alcohols. Full article

(This article belongs to the Special Issue Metal Oxide Catalysts: Synthesis and Applications)

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12 pages, 2543 KiB

Open AccessArticle

Fagonia cretica-Mediated Synthesis of Manganese Oxide (MnO₂) Nanomaterials Their Characterization and Evaluation of Their Bio-Catalytic and Enzyme Inhibition Potential for Maintaining Flavor and Texture in Apples

by Shah Faisal, Shahzar Khan, Abdullah, Sania Zafar, Muhammad Rizwan, Muhammad Ali, Riaz Ullah, Ghadeer M. Albadrani, Hanan R. H. Mohamed and Fazal Akbar

Catalysts 2022, 12(5), 558; https://doi.org/10.3390/catal12050558 - 19 May 2022

Cited by 25 | Viewed by 3212

Abstract

The apple is the most widely used fruit globally. Apples are more prone to fungal spoilage, which leads to browning and subsequent changes in their flavor and texture. Browning is also caused by the tyrosinase enzyme. By inhibiting tyrosinase initiation and fungal spoilage [...] Read more.

The apple is the most widely used fruit globally. Apples are more prone to fungal spoilage, which leads to browning and subsequent changes in their flavor and texture. Browning is also caused by the tyrosinase enzyme. By inhibiting tyrosinase initiation and fungal spoilage in fruits, the natural flavor and texture of fruits can be maintained. Biogenic NPs can act as antioxidants to inhibit tyrosinase and due to oxidative stress, it also catalyzes the deformation of fungal hyphae and spores. Nanotechnology is a research hotspot that has gained considerable interest due to its potential inferences in biosciences and food preservation technology. The present study aims to use biomass from the Fagonia cretica to create bio-inspired manganese oxide MnO₂ NPs and to evaluate its bio-catalytic potential for antifungal anti-browning through the inhibition of tyrosinase and its antioxidant potential for preserving apple flavor and texture. The green synthesized nanoparticles were extensively analyzed using UV spectroscopy, XRD, SEM, EDX, and FTIR techniques. Moreover, the synthesized manganese oxide nanoparticles (MnO₂ NPs) were evaluated for their bio-catalytic potential as anti-fungal and anti-spoiling agents. The values of antifungal activity among all the samples were 14.2 ± 86 mm, 8.9 ± 6.0 mm, 17.7 ± 1.26, and 20.7 ± 4.38 mm for Penicillium expansum, Monilinia fructigena, Penicillium chrysogenum, and Aspergillus oryzae at 200 µg/well, respectively. Moreover, the biogenic NPs were evaluated for their anti-browning potential through the inhibition of tyrosinase. MnO₂ NPs have been shown to have considerable inhibitory effects on tyrosinase up to 64.8 ± 0.16 at 200 µg/mL and (27.2 ± 0.58) at 25 µg/mL. Biogenic MnO₂ NPs can also act as antioxidants to inhibit tyrosinase and fungal growth by the formation of free radicals that damage the fungal hyphae and, as a result, slow down browning. The maximum DPPH free radical scavenging activity was 74.5 ± 0.39% at 200 µg/mL, and the minimum was 12.4 ± 0.27 at 25 µg/mL. The biogenic MnO₂ NPs are biocompatible and play a potent role in maintaining the flavor and texture of apples. Full article

(This article belongs to the Special Issue Catalysis for Flavours and Fragrances)

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22 pages, 1572 KiB

Open AccessReview

Photocatalytic Degradation of Recalcitrant Pollutants of Greywater

by Mohammad Aslam, Dawood Bin Fazal, Faizan Ahmad, Abdullah Bin Fazal, Ahmad Zuhairi Abdullah, Mukhtar Ahmed, Mohammad Qamar and Mohd Rafatullah

Catalysts 2022, 12(5), 557; https://doi.org/10.3390/catal12050557 - 18 May 2022

Cited by 11 | Viewed by 4248

Abstract

These days, many countries have a water shortage and have limited access to clean water. To overcome this, a new treatment is emerging, namely, the photocatalytic processing of greywater. Photocatalytic processes to remove the organic matter from different greywater sources are critically reviewed. [...] Read more.

These days, many countries have a water shortage and have limited access to clean water. To overcome this, a new treatment is emerging, namely, the photocatalytic processing of greywater. Photocatalytic processes to remove the organic matter from different greywater sources are critically reviewed. Their efficiency in degrading the organic matter in greywater is scrutinized along with factors that can affect the activity of photocatalysts. Modified TiO₂, ZnO and TiO₂ catalysts show great potential in degrading organic materials that are present in greywater. There are several methods that can be used to modify TiO₂ by using sol-gel, microwave and ultrasonication. Overall, the photocatalytic approach alone is not efficient in mineralizing the organic compounds, but it works well when the photocatalysis is combined with oxidants and Fe³⁺. However, factors such as pH, concentration and catalyst-loading of organic compounds can significantly affect photocatalytic efficiency. Full article

(This article belongs to the Special Issue Advances in Photoassisted and Photocatalytic Processes for Water Remediation)

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11 pages, 3515 KiB

Open AccessArticle

Facile Preparation of Porous Carbon Flake-Supported Nickel Nanoplates as Effective Catalysts for Methanol Electrooxidation

by Ali Aldalbahi, Mohamed H. El-Newehy, Hany El-Hamshary, Edmund Samuel and Sam S. Yoon

Catalysts 2022, 12(5), 556; https://doi.org/10.3390/catal12050556 - 18 May 2022

Cited by 1 | Viewed by 1837

Abstract

Herein, we report a facile and efficient method for fabricating porous carbon flakes (PCFs)-supported nickel nanoplates (Ni NPs) as electrocatalysts for methanol oxidation in alkaline media. The catalyst was fabricated in one step using molten salt synthesis. Various techniques were used to characterize [...] Read more.

Herein, we report a facile and efficient method for fabricating porous carbon flakes (PCFs)-supported nickel nanoplates (Ni NPs) as electrocatalysts for methanol oxidation in alkaline media. The catalyst was fabricated in one step using molten salt synthesis. Various techniques were used to characterize the morphology and composition of the Ni NPs@PCFs catalyst, and these revealed that the Ni NPs were dispersed finely across the PCFs with a highly crystalline structure. The Ni NPs@PCFs catalyst demonstrated high electrocatalytic activity for methanol oxidation (121 mA/cm² vs. Ag/AgCl), and it had an onset potential of 0.35 V. It also exhibited high stability in an alkaline electrolyte for the duration of the experiment (up to 2000 s). Full article

(This article belongs to the Special Issue Novel Catalyst Materials for Low-Temperature Fuel Cells and Electrolyzers)

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18 pages, 8250 KiB

Open AccessArticle

Highly Efficient and Selective Carbon-Doped BN Photocatalyst Derived from a Homogeneous Precursor Reconfiguration

by Qiong Lu, Jing An, Yandong Duan, Qingzhi Luo, Yunyun Shang, Qiunan Liu, Yongfu Tang, Jianyu Huang, Chengchun Tang, Rong Yin and Desong Wang

Catalysts 2022, 12(5), 555; https://doi.org/10.3390/catal12050555 - 18 May 2022

Cited by 9 | Viewed by 2795

Abstract

The modification of inert boron nitride by carbon doping to make it an efficient photocatalyst has been considered as a promising strategy. Herein, a highly efficient porous BCN (p-BCN) photocatalyst was synthesized via precursor reconfiguration based on the recrystallization of a new homogeneous [...] Read more.

The modification of inert boron nitride by carbon doping to make it an efficient photocatalyst has been considered as a promising strategy. Herein, a highly efficient porous BCN (p-BCN) photocatalyst was synthesized via precursor reconfiguration based on the recrystallization of a new homogeneous solution containing melamine diborate and glucose. Two crystal types of the p-BCN were obtained by regulating the recrystallization conditions of the homogeneous solution, which showed high photocatalytic activities and a completely different CO₂ reduction selectivity. The CO generation rate and selectivity of the p-BCN-1 were 63.1 μmol·g⁻¹·h⁻¹ and 54.33%; the corresponding values of the p-BCN-2 were 42.6 μmol·g⁻¹·h⁻¹ and 80.86%. The photocatalytic activity of the p-BCN was significantly higher than those of equivalent materials or other noble metals-loaded nanohybrids reported in the literature. It was found that the differences in the interaction sites between the hydroxyl groups in the boric acid and the homolateral hydroxyl groups in the glucose were directly correlated with the structures and properties of the p-BCN photocatalyst. We expect that the developed approach is general and could be extended to incorporate various other raw materials containing hydroxyl groups into the melamine diborate solution and could modulate precursors to obtain porous BN-based materials with excellent performance. Full article

(This article belongs to the Special Issue Advances in Heterojunction Photocatalysts)

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23 pages, 8445 KiB

Open AccessArticle

Synthetic Routes to Crystalline Complex Metal Alkyl Carbonates and Hydroxycarbonates via Sol–Gel Chemistry—Perspectives for Advanced Materials in Catalysis

by Schirin Hanf, Carlos Lizandara-Pueyo, Timo Philipp Emmert, Ivana Jevtovikj, Roger Gläser and Stephan Andreas Schunk

Catalysts 2022, 12(5), 554; https://doi.org/10.3390/catal12050554 - 18 May 2022

Cited by 3 | Viewed by 2712

Abstract

Metal alkoxides are easily available and versatile precursors for functional materials, such as solid catalysts. However, the poor solubility of metal alkoxides in organic solvents usually hinders their facile application in sol–gel processes and complicates access to complex carbonate or oxidic compounds after [...] Read more.

Metal alkoxides are easily available and versatile precursors for functional materials, such as solid catalysts. However, the poor solubility of metal alkoxides in organic solvents usually hinders their facile application in sol–gel processes and complicates access to complex carbonate or oxidic compounds after hydrolysis of the precursors. In our contribution we have therefore shown three different solubilization strategies for metal alkoxides, namely the derivatization, the hetero-metallization and CO₂ insertion. The latter strategy leads to a stoichiometric insertion of CO₂ into the metal–oxygen bond of the alkoxide and the subsequent formation of metal alkyl carbonates. These precursors can then be employed advantageously in sol–gel chemistry and, after controlled hydrolysis, result in chemically defined crystalline carbonates and hydroxycarbonates. Cu- and Zn-containing carbonates and hydroxycarbonates were used in an exemplary study for the synthesis of Cu/Zn-based bulk catalysts for methanol synthesis with a final comparable catalytic activity to commercial standard reference catalysts. Full article

(This article belongs to the Special Issue Synthesis and Application of Metal Mixed Oxide Catalysts (MMOs Catalysts))

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13 pages, 3607 KiB

Open AccessArticle

SnO₂/UV/H₂O₂ and TiO₂/UV/H₂O₂ Efficiency for the Degradation of Reactive Yellow 160A: By-Product Distribution, Cytotoxicity and Mutagenicity Evaluation

by Tasneem Kousar, Tanveer Hussain Bokhari, Awais Altaf, Atta ul Haq, Majid Muneer, Lamia Ben Farhat, Norah Alwadai, Nada Alfryyan, Muhammad Idrees Jilani, Munawar Iqbal, Muhammad I. Khan and Muhammad Kaleem Khosa

Catalysts 2022, 12(5), 553; https://doi.org/10.3390/catal12050553 - 18 May 2022

Cited by 11 | Viewed by 2367

Abstract

Advanced oxidation processes (AOPs) have emerged as a promising approach for the removal of organic dyes from effluents. Different AOPs were employed for the degradation of Reactive Yellow 160A (RY-160A) dye, i.e., SnO₂/UV/H₂O₂ and TiO₂/UV/H₂ [...] Read more.

Advanced oxidation processes (AOPs) have emerged as a promising approach for the removal of organic dyes from effluents. Different AOPs were employed for the degradation of Reactive Yellow 160A (RY-160A) dye, i.e., SnO₂/UV/H₂O₂ and TiO₂/UV/H₂O₂. In the case of UV treatment, maximum degradation of 28% was observed, while UV/H₂O₂ furnished 77.78% degradation, and UV/H₂O₂/TiO₂ degraded the RY-160A dye up to 90.40% (RY-160A 30 mg/L, 0.8 mL of H₂O₂). The dye degradation was 82.66% in the case of UV/H₂O₂/SnO₂ at pH 3. FTIR and LC-MS analyses were performed in order to monitor the degradation by-products. The cytotoxicity and mutagenicity of RY-160A dye were evaluated by hemolytic and Ames (TA98 and TA100 strains) assays. It was observed that the RY-160A dye solution was toxic before treatment, and toxicity was reduced significantly after treatment. Results indicated that UV/H₂O₂/TiO₂ is more efficient at degrading RY-160A versus other AOPs, which have potential application for the remediation of dyes in textile effluents. Full article

(This article belongs to the Section Environmental Catalysis)

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15 pages, 3400 KiB

Open AccessArticle

Assessment of a Novel Photocatalytic TiO₂-Zirconia Ultrafiltration Membrane and Combination with Solar Photo-Fenton Tertiary Treatment of Urban Wastewater

by Dennis Deemter, Fabricio Eduardo Bortot Coelho, Isabel Oller, Sixto Malato and Ana M. Amat

Catalysts 2022, 12(5), 552; https://doi.org/10.3390/catal12050552 - 18 May 2022

Cited by 4 | Viewed by 2527

Abstract

The objective of this study was to assess the combination of a photocatalytic TiO₂-coated ZrO₂ UF membrane with solar photo-Fenton treatment at circumneutral pH for the filtration and treatment of urban wastewater treatment plant (UWWTP) effluents. Photocatalytic self-cleaning properties were [...] Read more.

The objective of this study was to assess the combination of a photocatalytic TiO₂-coated ZrO₂ UF membrane with solar photo-Fenton treatment at circumneutral pH for the filtration and treatment of urban wastewater treatment plant (UWWTP) effluents. Photocatalytic self-cleaning properties were tested with a UWWTP effluent under irradiation in a solar simulator. Then, both the permeates and retentates from the membrane process were treated using the solar photo-Fenton treatment. The UWWTP effluent was spiked with caffeine (CAF), imidacloprid (IMI), thiacloprid (THI), carbamazepine (CBZ) and diclofenac (DCF) at an initial concentration of 100 µg/L each. Retention on the membrane of Pseudomonas Aeruginosa (P. Aeruginosa), a Gram-negative bacterial strain, was tested with and without irradiation. It was demonstrated that filtration of a certain volume of UWWTP effluent in the dark is possible, and the original conditions can then be recovered after illumination. The photocatalytic membrane significantly reduces the turbidity of the UWWTP effluent, significantly increasing the degradation efficiency of the subsequent solar photo-Fenton treatment. The results showed that the membrane allowed consistent retention of P. Aeruginosa at an order of magnitude of 1 × 10³–1 × 10⁴ CFU/mL. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Water Pollutants)

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10 pages, 1641 KiB

Open AccessCommunication

Continuous Flow Glycolipid Synthesis Using a Packed Bed Reactor

by Rebecca Hollenbach, Delphine Muller, André Delavault and Christoph Syldatk

Catalysts 2022, 12(5), 551; https://doi.org/10.3390/catal12050551 - 18 May 2022

Cited by 5 | Viewed by 2210

Abstract

Glycolipids are a class of biodegradable biosurfactants that are non-toxic and based on renewables, making them a sustainable alternative to petrochemical surfactants. Enzymatic synthesis allows a tailor-made production of these versatile compounds using sugar and fatty acid building blocks with rationalized structures for [...] Read more.

Glycolipids are a class of biodegradable biosurfactants that are non-toxic and based on renewables, making them a sustainable alternative to petrochemical surfactants. Enzymatic synthesis allows a tailor-made production of these versatile compounds using sugar and fatty acid building blocks with rationalized structures for targeted applications. Therefore, glycolipids can be comprehensively designed to outcompete conventional surfactants regarding their physicochemical properties. However, enzymatic glycolipid processes are struggling with both sugars and fatty acid solubilities in reaction media. Thus, continuous flow processes represent a powerful tool in designing efficient syntheses of sugar esters. In this study, a continuous enzymatic glycolipid production catalyzed by Novozyme 435^® is presented as an unprecedented concept. A biphasic aqueous–organic system was investigated, allowing for the simultaneous solubilization of sugars and fatty acids. Owing to phase separation, the remaining non-acylated glucose was easily separated from the product stream and was refed to the reactor forming a closed-loop system. Productivity in the continuous process was higher compared to a batch one, with space–time yields of up to 1228 ± 65 µmol/L/h. A temperature of 70 °C resulted in the highest glucose-6-O-decanoate concentration in the Packed Bed Reactor (PBR). Consequently, the design of a continuous biocatalytic production is a step towards a more competitive glycolipid synthesis in the aim for industrialization. Full article

(This article belongs to the Special Issue Biocatalysis in Non-conventional Media)

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16 pages, 5627 KiB

Open AccessArticle

Stability of a NiAl₂O₄ Derived Catalyst in the Ethanol Steam Reforming in Reaction-Regeneration Cycles: Effect of Reduction Temperature

by Sergio Iglesias-Vázquez, José Valecillos, Aingeru Remiro, Javier Bilbao and Ana Guadalupe Gayubo

Catalysts 2022, 12(5), 550; https://doi.org/10.3390/catal12050550 - 17 May 2022

Cited by 8 | Viewed by 2772

Abstract

The catalyst regeneration is still a challenge to make the ethanol steam reforming (ESR) process feasible for sustainable H₂ production. NiAl₂O₄ spinel derived catalysts are highly active and selective for ESR, but they require avoiding irreversible deactivation to ensure [...] Read more.

The catalyst regeneration is still a challenge to make the ethanol steam reforming (ESR) process feasible for sustainable H₂ production. NiAl₂O₄ spinel derived catalysts are highly active and selective for ESR, but they require avoiding irreversible deactivation to ensure their regeneration. Their stability depends on the catalyst structure, and herein we report different Ni/Al₂O₃-NiAl₂O₄ catalysts obtained upon reduction of a NiAl₂O₄ spinel at 700, 750, or 850 °C. The catalysts were tested in ESR reaction-regeneration cycles, with reaction at 600 °C and regeneration by coke combustion at 850 °C followed by reduction at the corresponding temperature. The fresh, spent, and regenerated catalysts were characterized using X-ray diffraction, N₂ physisorption, temperature programmed reduction and oxidation, and scanning electron microscopy. The irreversible deactivation is due to Ni volatilization and catalyst particle fragmentation. These phenomena are prompted by a high filamentous carbon deposition favored by the Al₂O₃ content in the catalyst. The reduction in the 700–750 °C range is optimum for controlling the Al₂O₃ content, increasing the NiAl₂O₄/Al₂O₃ ratio in the resulting catalyst. These catalysts show a period of partial reversible deactivation by coke with a change in the H₂ formation mechanism reaching a pseudo-stable state with a H₂ yield of 40% and a reproducible performance in successive reaction-regeneration cycles. Full article

(This article belongs to the Section Catalysis for Sustainable Energy)

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12 pages, 6220 KiB

Open AccessArticle

Ce_1−xFe_xVO₄ with Improved Activity for Catalytic Reduction of NO with NH₃

by Li Wang, Junbo Wang, Heping Cheng, Xiangxiang Zhou and Zhen Ma

Catalysts 2022, 12(5), 549; https://doi.org/10.3390/catal12050549 - 17 May 2022

Cited by 1 | Viewed by 1970

Abstract

A series of Ce_1−xFe_xVO₄ (x = 0, 0.25, 0.50, 0.75, 1) catalysts prepared by modified hydrothermal synthesis were used for selective catalytic reduction (SCR) of NO_x with NH₃. Among them, Ce_0.5Fe_0.5VO [...] Read more.

A series of Ce_1−xFe_xVO₄ (x = 0, 0.25, 0.50, 0.75, 1) catalysts prepared by modified hydrothermal synthesis were used for selective catalytic reduction (SCR) of NO_x with NH₃. Among them, Ce_0.5Fe_0.5VO₄ showed the highest catalytic activity. The catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction using H₂ (H₂-TPR), and temperature-programmed desorption of NH₃ (NH₃-TPD). The results indicated the formation of Ce-Fe-V-O solid solutions. The average oxidation states (AOS) of Ce, Fe, V, and O atoms changed obviously with the incorporation of Fe³⁺ into CeVO₄, and the acidity of Ce_0.5Fe_0.5VO₄ differs from that of CeVO₄ and FeVO₄. The presence of more acid sites and a sharp increase in active oxygen species in Ce_0.5Fe_0.5VO₄ effectively improved the selective catalytic reduction (SCR) activity. Full article

(This article belongs to the Section Catalytic Materials)

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19 pages, 6448 KiB

Open AccessFeature PaperArticle

Nitrogen and Sulfur Co-Doped Graphene Quantum Dots Anchored TiO₂ Nanocomposites for Enhanced Photocatalytic Activity

by Jishu Rawal, Urooj Kamran, Mira Park, Bishweshwar Pant and Soo-Jin Park

Catalysts 2022, 12(5), 548; https://doi.org/10.3390/catal12050548 - 17 May 2022

Cited by 15 | Viewed by 3540

Abstract

Herein, nitrogen (N) and sulfur (S) co-doped graphene quantum dots (GQDs) using different one-dimensional (1-D) carbon nanomaterials as precursors were synthesized, followed by heterojunction formation with TiO₂. GQDs exhibit unlike physiochemical properties due to the disproportionate ratio of N and S [...] Read more.

Herein, nitrogen (N) and sulfur (S) co-doped graphene quantum dots (GQDs) using different one-dimensional (1-D) carbon nanomaterials as precursors were synthesized, followed by heterojunction formation with TiO₂. GQDs exhibit unlike physiochemical properties due to the disproportionate ratio of N and S heteroatoms and dissimilar reaction parameters. Tailored type-II band gap (E_g) alignment was formed with narrowed E_g value that improves photogenerated electron transfer due to π-conjugation. GQDs-TiO₂ nanocomposites exhibit remarkably high methylene blue (MB) degradation up to 99.78% with 2.3–3 times elevated rate constants as compared with TiO₂. CNF-GQDs-TiO₂ demonstrates the fastest MB degradation (60 min) due to the synergistic effect of nitrogen and sulfur doping, and is considered the most stable photocatalyst among prepared nanocomposites as tested up to three cyclic runs. Whereas, C–O–Ti bonds were not only responsible for nanocomposites strengthening but also provide a charge transfer pathway. Moreover, charge transport behavior, generation of active species, and reaction mechanism were scrutinized via free-radical scavenger analysis. Full article

(This article belongs to the Special Issue Catalytic Processes for Water and Wastewater Treatment)

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27 pages, 14374 KiB

Open AccessReview

Recent Advances in the Synthesis of Five-Membered Cyclic Carbonates and Carbamates from Allylic or Propargylic Substrates and CO₂

by Filip Vranješević, Maria Kolympadi Markovic, Dario Matulja, Gabriela Ambrožić, José Ángel Sordo, Sylvain Laclef, Valerije Vrček and Dean Marković

Catalysts 2022, 12(5), 547; https://doi.org/10.3390/catal12050547 - 17 May 2022

Cited by 5 | Viewed by 3750

Abstract

The organic carbamates and carbonates are highly desirable compounds that have found a wide range of applications in drug design, medicinal chemistry, material science, and the polymer industry. The development of new catalytic carbonate and carbamate forming reactions, which employ carbon dioxide as [...] Read more.

The organic carbamates and carbonates are highly desirable compounds that have found a wide range of applications in drug design, medicinal chemistry, material science, and the polymer industry. The development of new catalytic carbonate and carbamate forming reactions, which employ carbon dioxide as a cheap, green, abundant, and easily available reagent, would thus represent an ideal substitution for existing methods. In this review, the advancements in the catalytic conversion of allylic and propargylic alcohols and amines to corresponding five-membered cyclic carbonates and carbamates are summarized. Both the metal- and the organocatalyzed methods are reviewed, as well as the proposed mechanisms and key intermediates of the illustrated carbonate and carbamate forming reactions. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Pierre Vogel)

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20 pages, 4046 KiB

Open AccessFeature PaperArticle

Expanding Access to Optically Active Non-Steroidal Anti-Inflammatory Drugs via Lipase-Catalyzed KR of Racemic Acids Using Trialkyl Orthoesters as Irreversible Alkoxy Group Donors

by Beata Zdun, Piotr Cieśla, Jan Kutner and Paweł Borowiecki

Catalysts 2022, 12(5), 546; https://doi.org/10.3390/catal12050546 - 17 May 2022

Cited by 5 | Viewed by 3971

Abstract

Studies into the enzymatic kinetic resolution (EKR) of 2-arylpropanoic acids (‘profens’), as the active pharmaceutical ingredients (APIs) of blockbuster non-steroidal anti-inflammatory drugs (NSAIDs), by using various trialkyl orthoesters as irreversible alkoxy group donors in organic media, were performed. The enzymatic reactions of target [...] Read more.

Studies into the enzymatic kinetic resolution (EKR) of 2-arylpropanoic acids (‘profens’), as the active pharmaceutical ingredients (APIs) of blockbuster non-steroidal anti-inflammatory drugs (NSAIDs), by using various trialkyl orthoesters as irreversible alkoxy group donors in organic media, were performed. The enzymatic reactions of target substrates were optimized using several different immobilized preparations of lipase type B from the yeast Candida antarctica (CAL-B). The influence of crucial parameters, including the type of enzyme and alkoxy agent, as well as the nature of the organic co-solvent and time of the process on the conversion and enantioselectivity of the enzymatic kinetic resolution, is described. The optimal EKR procedure for the racemic profens consisted of a Novozym 435-STREM lipase preparation suspended in a mixture of 3 equiv of trimethyl or triethyl orthoacetate as alkoxy donor and toluene or n-hexane as co-solvent, depending on the employed racemic NSAIDs. The reported biocatalytic system provided optically active products with moderate-to-good enantioselectivity upon esterification lasting for 7–48 h, with most promising results in terms of enantiomeric purity of the pharmacologically active enantiomers of title APIs obtained on the analytical scale for: (S)-flurbiprofen (97% ee), (S)-ibuprofen (91% ee), (S)-ketoprofen (69% ee), and (S)-naproxen (63% ee), respectively. In turn, the employment of optimal conditions on a preparative-scale enabled us to obtain the (S)-enantiomers of: flurbiprofen in 28% yield and 97% ee, ibuprofen in 45% yield and 56% ee, (S)-ketoprofen in 23% yield and 69% ee, and naproxen in 42% yield and 57% ee, respectively. The devised method turned out to be inefficient toward racemic etodolac regardless of the lipase and alkoxy group donor used, proving that it is unsuitable for carboxylic acids possessing tertiary chiral centers. Full article

(This article belongs to the Special Issue Applications of Hydrolases in Medicinal Chemistry)

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17 pages, 3840 KiB

Open AccessArticle

Tuning the Electronic Properties of Homoleptic Silver(I) bis-BIAN Complexes towards Efficient Electrocatalytic CO₂ Reduction

by Dominik Krisch, He Sun, Kevinjeorjios Pellumbi, Kirill Faust, Ulf-Peter Apfel and Wolfgang Schöfberger

Catalysts 2022, 12(5), 545; https://doi.org/10.3390/catal12050545 - 17 May 2022

Cited by 7 | Viewed by 2999

Abstract

We report herein the preparation and characterization of six readily assembled bis-coordinated homoleptic silver(I) N,N′-bis(arylimino)acenaphthene (BIAN) complexes of general structure [Ag(I)(BIAN)₂]BF₄ and the influence of the electronic properties of the ligand substitution pattern on their performance in [...] Read more.

We report herein the preparation and characterization of six readily assembled bis-coordinated homoleptic silver(I) N,N′-bis(arylimino)acenaphthene (BIAN) complexes of general structure [Ag(I)(BIAN)₂]BF₄ and the influence of the electronic properties of the ligand substitution pattern on their performance in electrochemical CO₂ reduction (CO₂R). All the explored catalysts displayed substantial current enhancements in carbon-dioxide-saturated solvents dependent on the ligated BIAN and no significant concurrent H₂ evolution when utilizing 2% H₂O as a proton source. Additionally, preliminary studies, employing a drop-casted ink of 0.4 mg cm⁻² [Ag(I)(4-OMe-BIAN)₂]BF₄ (Ag4) immobilized onto carbon paper gas diffusion electrodes in a flow cell with 1M KHCO₃ aqueous electrolyte, resulted in a propitious Faradaic efficiency of 51% for CO at a current density of 50 mA cm⁻². Full article

(This article belongs to the Section Electrocatalysis)

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