Catalysts

13 pages, 3413 KiB

Open AccessArticle

Supported Cu/W/Mo/Ni—Liquid Metal Catalyst with Core-Shell Structure for Photocatalytic Degradation

by Shuting Liang, Chaowei Wang, Fengjiao Li and Gang Song

Catalysts 2021, 11(11), 1419; https://doi.org/10.3390/catal11111419 - 22 Nov 2021

Cited by 9 | Viewed by 2609

Room-temperature liquid metal is a very ideal material for the design of catalytic materials. At low temperatures, the liquid metal enters the liquid state. It provides an opportunity to utilize the liquid phase in the catalysis, which is far superior to the traditional [...] Read more.

Room-temperature liquid metal is a very ideal material for the design of catalytic materials. At low temperatures, the liquid metal enters the liquid state. It provides an opportunity to utilize the liquid phase in the catalysis, which is far superior to the traditional solid-phase catalyst. Aiming at the low performance and narrow application scope of the existing single-phase liquid metal catalyst, this paper proposed a type of liquid metal/metal oxide core-shell composite multi-metal catalyst. The Ga₂O₃ core-shell heterostructure was formed by chemical modification of liquid metals with different nano metals Cu/W/Mo/Ni, and it was applied to photocatalytic degrading organic contaminated raw liquor. The effects of different metal species on the rate of catalytic degradation were explored. The selectivity and stability of the LM/MO core-shell composite catalytic material were clarified, and it was found that the Ni-LM catalyst could degrade methylene blue and Congo red by 92% and 79%, respectively. The catalytic mechanism and charge transfer mechanism were revealed by combining the optical band gap value. Finally, we provided a theoretical basis for the further development of liquid metal photocatalytic materials in the field of new energy environments. Full article

(This article belongs to the Topic Nanomaterials for Sustainable Energy Applications)

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12 pages, 3217 KiB

Open AccessArticle

Ceramized Fabrics and Their Integration in a Semi-Pilot Plant for the Photodegradation of Water Pollutants

by Lara Faccani, Simona Ortelli, Magda Blosi and Anna Luisa Costa

Catalysts 2021, 11(11), 1418; https://doi.org/10.3390/catal11111418 - 22 Nov 2021

Cited by 5 | Viewed by 1834

Abstract

The use of nano-photocatalysts for the water/wastewater purifications, particularly in developing regions, offers promising advantages over conventional technologies. TiO₂-based photocatalysts deposited on fabrics represent an efficient solution for obtaining heterogeneous photocatalysts, which are easily adaptable in the already installed water treatment [...] Read more.

The use of nano-photocatalysts for the water/wastewater purifications, particularly in developing regions, offers promising advantages over conventional technologies. TiO₂-based photocatalysts deposited on fabrics represent an efficient solution for obtaining heterogeneous photocatalysts, which are easily adaptable in the already installed water treatment plants or air purification systems. Despite the huge effort spent to develop and characterize novel nano-photocatalysts, which are especially active under solar light, knowledge gaps still persist for their full-scale application, starting from the reactor design and scale-up and the evaluation of the photocatalytic efficiency in pre-pilot scenarios. In this study, we offered easily scalable solutions for adapting TiO₂-based photocatalysts, which are deposited on different kinds of fabrics and implemented in a 6 L semi-pilot plant, using the photodegradation of Rhodamine B (RhB) as a model of water pollution. We took advantage of a multi-variable optimization approach to identify the best design options in terms of photodegradation efficiency and turnover frequency (TOF). Surprisingly, in the condition of use, the irradiation with a light-emitting diode (LED) visible lamp appeared as a valid alternative to the use of UV LED. The identification of the best design options in the semi-pilot plant allowed scaling up the technology in a 100 L pilot plant suitable for the treatment of industrial wastewater. Full article

(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)

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20 pages, 2524 KiB

Open AccessFeature PaperArticle

Understanding of the Key Factors Determining the Activity and Selectivity of CuZn Catalysts in Hydrogenolysis of Alkyl Esters to Alcohols

by Oleg Kikhtyanin, Jaroslav Aubrecht, Violetta Pospelova and David Kubička

Catalysts 2021, 11(11), 1417; https://doi.org/10.3390/catal11111417 - 22 Nov 2021

Cited by 4 | Viewed by 1780

Abstract

CuZn catalysts are perspective catalysts for esters hydrogenolysis, but more knowledge is needed to optimize their catalytic performance. In this work, we consider the impact of CuZn catalysts composition on their structure, activity, selectivity, and stability in esters hydrogenolysis. Four catalysts with various [...] Read more.

CuZn catalysts are perspective catalysts for esters hydrogenolysis, but more knowledge is needed to optimize their catalytic performance. In this work, we consider the impact of CuZn catalysts composition on their structure, activity, selectivity, and stability in esters hydrogenolysis. Four catalysts with various Cu/Zn ratio were synthesized by a co-precipitation and characterized in as-prepared, calcined, reduced, and spent state by XRF, XRD, N₂ physisorption, CO₂-TPD, NH₃-TPD, and N₂O chemisorption. XRD data revealed the effect of the composition on the size of Cu and ZnO particles. The catalytic performance was investigated using an autoclave. All catalysts exhibited high methyl hexanoate conversion about 48–60% after 3 h but their activity and selectivity were found to be dependent on Cu/Zn ratio. The conversion of methyl hexanoate and hexyl hexanoate was compared to explain the observed product selectivity. Moreover, the catalysts stability was investigated in three consecutive reaction cycles and correlated with changes in the size of constituent particles. Moreover, when different esters were tested, a slight decrease in conversion and increase in alcohol selectivity with a growth in molecule size was observed. Obtained results allow making a conclusion about the optimal composition that provides the good performance of CuZn catalysts in ester hydrogenolysis. Full article

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16 pages, 4466 KiB

Open AccessArticle

A Study on the Characteristic and Antibacterial Activity of Ti₃O_x Thin Films

by Endrika Widyastuti, Fu-Yang Xu, Chen-Tien Chiu, Jhen-Hau Jan, Jue-Liang Hsu and Ying-Chieh Lee

Catalysts 2021, 11(11), 1416; https://doi.org/10.3390/catal11111416 - 22 Nov 2021

Cited by 4 | Viewed by 1899

Abstract

A pure Ti target in Ar/O₂ gas mixture was used to synthesize Ti₃O_x thin film on a glass substrate by Reactive High-Power Impulse Magnetron Sputtering (HiPIMS) under different sputtering power (2 and 2.5 kW). The influence of HiPIMS parameters [...] Read more.

A pure Ti target in Ar/O₂ gas mixture was used to synthesize Ti₃O_x thin film on a glass substrate by Reactive High-Power Impulse Magnetron Sputtering (HiPIMS) under different sputtering power (2 and 2.5 kW). The influence of HiPIMS parameters on thin films’ structural, morphological, chemical composition, optical and photocatalytic, and antibacterial properties was investigated. In this study, Ti₃O_x thin films can be synthesized using the HiPIMS method without the post-annealing process. Two co-existence phases (hexagonal Ti₃O and base-centered monoclinic Ti₃O₅ phases) existed on the Ti₃O_x films. It is found that the peak intensity of (006) Ti₃O hexagonal slightly increased as the sputtering power increased from 2 to 2.5 kW. The Ti₃O_x thin-film bandgap values were 3.36 and 3.50 eV for 2 and 2.5 kW, respectively. The Ti₃O_x films deposited at 2.5 kW showed good photocatalytic activity under UV light irradiation, with a higher methylene blue dye degradation rate than TiO₂ thin films. The antibacterial study on Ti₃O_x thin films exhibited a high inhibition percentage against E. coli and S. aureus. This study demonstrates that Ti₃O_x thin films can promote high photocatalytic and antibacterial activity. Full article

(This article belongs to the Special Issue Photocatalytic Nanomaterials for Abatement of Microorganisms)

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17 pages, 1594 KiB

Open AccessArticle

Figures of Merit for Photocatalysis: Comparison of NiO/La-NaTaO₃ and Synechocystis sp. PCC 6803 as a Semiconductor and a Bio-Photocatalyst for Water Splitting

by Eike S. Welter, Sebastian Kött, Fabian Brandenburg, Jens Krömer, Michael Goepel, Andreas Schmid and Roger Gläser

Catalysts 2021, 11(11), 1415; https://doi.org/10.3390/catal11111415 - 22 Nov 2021

Cited by 5 | Viewed by 2119

Abstract

While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO [...] Read more.

While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO₃) and a bio-photocatalyst (Synechocystis sp. PCC 6803) in the same setup under similar reaction conditions, eliminating the often ill-defined influence of the setup on the FOMs obtained. Comparing the results enables the critical evaluation of existing FOMs and a quantitative comparison of both photocatalytic systems. A single FOM is insufficient to compare the photocatalysts, instead a combination of multiple FOMs (reaction rate, photocatalytic space time yield and a redefined apparent quantum yield) is superior for assessing a variety of photocatalytic systems. Full article

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

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15 pages, 4292 KiB

Open AccessArticle

Au@CoS-BiVO₄ {010} Constructed for Visible-Light-Assisted Peroxymonosulfate Activation

by Yekun Ji, Ye Zhou, Jinnan Wang, Aimin Li, Weilin Bian and Philippe François-Xavier Corvini

Catalysts 2021, 11(11), 1414; https://doi.org/10.3390/catal11111414 - 22 Nov 2021

Cited by 8 | Viewed by 1964

Abstract

A visible-light-Fenton-like reaction system was constructed for the selective conversion of peroxymonosulfate to sulfate radical. Au@CoS, when doped on monoclinic BiVO₄ {010} facets, promoted spatial charge separation due to the different energy band between the m-BiVO₄ {010} and {110} facets. The [...] Read more.

A visible-light-Fenton-like reaction system was constructed for the selective conversion of peroxymonosulfate to sulfate radical. Au@CoS, when doped on monoclinic BiVO₄ {010} facets, promoted spatial charge separation due to the different energy band between the m-BiVO₄ {010} and {110} facets. The visible-light response of m-BiVO₄ was enhanced, which was attributed to the SPR effect of Au. And the photogenerated electrons were transferred from the m-BiVO₄ {010} facet to Au via a Schottky junction. Owing to higher work function, CoS was able to capture these photoelectrons with acceleration of the Co(Ⅱ)/Co(Ⅲ) redox, enhancing peroxymonosulfate conversion to sulfate radical (Co²⁺ + HSO₅⁻→ Co³⁺ + •SO₄⁻ + OH⁻). On the other hand, holes accumulated on m-BiVO₄ {110} facets also contributed to organics oxidation. Thus, more than 95% of RhB was degraded within 40 min, and, even after five cycles, over 80% of RhB could be removed. The radical trapping experiments and EPR confirmed that both the sulfate radical and photogenerated hole were the main species for organics degradation. UV-vis DRS, photoluminescence (PL) and photoelectrochemical analyses also confirmed the enhancement of the visible-light response and charge separation. In a pilot scale experiment (PMS = 3 mM, initial TOC = 151 mg/L, reaction time = 4 h), CoS-Au-BiVO₄ loaded on glass fiber showed a high mineralization rate (>60%) of practical wastewater. Full article

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11 pages, 2214 KiB

Open AccessFeature PaperArticle

Revisiting Gas to Solids Ratio for Activated Sludge Clarification by Electrolytic Hydrogen Bubbles: Theoretical and Experimental Evaluations

by Jiseon Kim, Chong Min Chung, Kangwoo Cho and Tai Hak Chung

Catalysts 2021, 11(11), 1413; https://doi.org/10.3390/catal11111413 - 22 Nov 2021

Cited by 3 | Viewed by 1818

Abstract

Molecular hydrogen (H₂), as the green energy carrier from water electrolysis, can be utilized for separation of suspended micro-particles as electroflotation (EF). This study provides practical guidelines for the gas to solids (G/S) ratio as the governing parameter in EF, based [...] Read more.

Molecular hydrogen (H₂), as the green energy carrier from water electrolysis, can be utilized for separation of suspended micro-particles as electroflotation (EF). This study provides practical guidelines for the gas to solids (G/S) ratio as the governing parameter in EF, based on theoretical estimations and experiments for clarification of activated sludge. The G/S ratio in EF was controlled linearly by current density (j), under quasi-consistent current efficiency (at j > 8 mA/cm²) for H₂ (~1) and O₂ (~0.4) bubble generations on Ti cathode and IrTaO_x anode, respectively. Based on the measured sizes of bubbles (approximated to 35 µm) and biological flocs (discretized to mean sizes of 22.5, 40, 60, 135, and 150 µm), batch flotation experiments estimated the maximum collision-attachment efficiency of 0.057. The rise velocities of floc-bubble aggregate were computed to derive the limiting G/S ratio to overcome the given influent hydraulic loading. Consequently, the estimates (5.23 × 10⁻⁴ and 5.92 × 10⁻⁴ at hydraulic loading of 0.87 and 1.73 cm/min, respectively) were compatible with the continuous EF experiments. Full article

(This article belongs to the Special Issue Applications of Electrocatalysts for Water Treatment: Recent Advances)

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14 pages, 2870 KiB

Open AccessArticle

Methanation of CO₂ Using MIL-53-Based Catalysts: Ni/MIL-53–Al₂O₃ versus Ni/MIL-53

by Oana Grad, Gabriela Blanita, Mihaela D. Lazar and Maria Mihet

Catalysts 2021, 11(11), 1412; https://doi.org/10.3390/catal11111412 - 21 Nov 2021

Cited by 5 | Viewed by 2418

Abstract

MIL-53 and the MIL-53–Al₂O₃ composite synthesized by a solvothermal procedure, with water as the only solvent besides CrCl₃ and benzene-1,4-dicarboxylic acid (BDC), were used as catalytic supports to obtain the novel MIL-53-based catalysts Ni(10 wt.%)/MIL-53 and Ni(10 wt.%)/MIL-53–Al₂ [...] Read more.

MIL-53 and the MIL-53–Al₂O₃ composite synthesized by a solvothermal procedure, with water as the only solvent besides CrCl₃ and benzene-1,4-dicarboxylic acid (BDC), were used as catalytic supports to obtain the novel MIL-53-based catalysts Ni(10 wt.%)/MIL-53 and Ni(10 wt.%)/MIL-53–Al₂O₃. Ni nanoparticle deposition by an adapted double-solvent method leads to the uniform distribution of metallic particles, both smaller (≤10 nm) and larger ones (10–30 nm). MIL-53–Al₂O₃ and Ni/MIL-53–Al₂O₃ show superior thermal stability to MIL-53 and Ni/MIL-53, while MIL-53–Al₂O₃ samples combine the features of both MIL-53 and alumina in terms of porosity. The investigation of temperature’s effect on the catalytic performance in the methanation process (CO₂:H₂ = 1:5.2, GHSV = 4650 h⁻¹) revealed that Ni/MIL-53 is more active at temperatures below 300 °C, and Ni/MIL-53–Al₂O₃ above 300 °C. Both catalysts show maximum CO₂ conversion at 350 °C: 75.5% for Ni/MIL-53 (methane selectivity of 93%) and 88.8% for Ni/MIL-53–Al₂O₃ (methane selectivity of 98%). Stability tests performed at 280 °C prove that Ni/MIL-53–Al₂O₃ is a possible candidate for the CO₂ methanation process due to its high CO₂ conversion and CH₄ selectivity, corroborated by the preservation of the structure and crystallinity of MIL-53 after prolonged exposure in the reaction medium. Full article

(This article belongs to the Special Issue Frontiers in Catalysis for CO₂ Methanation)

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14 pages, 5594 KiB

Open AccessFeature PaperArticle

Ethanol Dehydrogenation to Acetaldehyde over Co@N-Doped Carbon

by Aleksey N. Chernov, Tatiana V. Astrakova, Konstantin Yu. Koltunov and Vladimir I. Sobolev

Catalysts 2021, 11(11), 1411; https://doi.org/10.3390/catal11111411 - 21 Nov 2021

Cited by 5 | Viewed by 2077

Abstract

Cobalt and nitrogen co-doped carbon materials (Co@CN) have recently attracted significant attention as highly efficient noble-metal-free catalysts exhibiting a large application range. In a similar research interest, and taking into account the ever-increasing importance of bioethanol as a renewable raw material, here, we [...] Read more.

Cobalt and nitrogen co-doped carbon materials (Co@CN) have recently attracted significant attention as highly efficient noble-metal-free catalysts exhibiting a large application range. In a similar research interest, and taking into account the ever-increasing importance of bioethanol as a renewable raw material, here, we report the results on ethanol dehydrogenation to acetaldehyde over Co@NC catalysts. The catalyst samples were synthesized by a variety of affordable techniques, ensuring generation of various types of Co species incorporated in carbon, such as subnanosized cobalt sites and nano-sized particles of metallic cobalt and cobalt oxides. The catalytic activity was tested under both oxidative and non-oxidative gas-phase conditions at 200–450 °C using a fixed-bed flow reactor. The non-oxidative conditions proved to be much more preferable for the target reaction, competing, however, with ethanol dehydration to ethylene. Under specified reaction conditions, ethanol conversion achieved a level of 66% with 84% selectivity to acetaldehyde at 400 °C. The presence of molecular oxygen in the feed led mainly to deep oxidation of ethanol to CO_x, giving acetaldehyde in a comparatively low yield. The potential contribution of carbon itself and supported cobalt forms to the observed reaction pathways is discussed. Full article

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16 pages, 1702 KiB

Open AccessEditor’s ChoiceArticle

Application Potential of Cyanide Hydratase from Exidia glandulosa: Free Cyanide Removal from Simulated Industrial Effluents

by Anastasia Sedova, Lenka Rucká, Pavla Bojarová, Michaela Glozlová, Petr Novotný, Barbora Křístková, Miroslav Pátek and Ludmila Martínková

Catalysts 2021, 11(11), 1410; https://doi.org/10.3390/catal11111410 - 21 Nov 2021

Cited by 6 | Viewed by 2234

Abstract

Industries such as mining, cokemaking, (petro)chemical and electroplating produce effluents that contain free cyanide (fCN = HCN + CN⁻). Currently, fCN is mainly removed by (physico)chemical methods or by biotreatment with activated sludge. Cyanide hydratases (CynHs) (EC 4.2.1.66), which convert fCN [...] Read more.

Industries such as mining, cokemaking, (petro)chemical and electroplating produce effluents that contain free cyanide (fCN = HCN + CN⁻). Currently, fCN is mainly removed by (physico)chemical methods or by biotreatment with activated sludge. Cyanide hydratases (CynHs) (EC 4.2.1.66), which convert fCN to the much less toxic formamide, have been considered for a mild approach to wastewater decyanation. However, few data are available to evaluate the application potential of CynHs. In this study, we used a new CynH from Exidia glandulosa (protein KZV92691.1 designated NitEg by us), which was overproduced in Escherichia coli. The purified NitEg was highly active for fCN with 784 U/mg protein, k_cat 927/s and k_cat/K_M 42/s/mM. It exhibited optimal activities at pH approximately 6–9 and 40–45 °C. It was quite stable in this pH range, and retained approximately 40% activity at 37 °C after 1 day. Silver and copper ions (1 mM) decreased its activity by 30–40%. The removal of 98–100% fCN was achieved for 0.6–100 mM fCN. Moreover, thiocyanate, sulfide, ammonia or phenol added in amounts typical of industrial effluents did not significantly reduce the fCN conversion, while electroplating effluents may need to be diluted due to high fCN and metal content. The ease of preparation of NitEg, its high specific activity, robustness and long shelf life make it a promising biocatalyst for the detoxification of fCN. Full article

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

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17 pages, 3188 KiB

Open AccessArticle

Synthesis and Catalytic Properties of Novel Ruthenacarboranes Based on nido-[5-Me-7,8-C₂B₉H₁₀]²⁻ and nido-[5,6-Me₂-7,8-C₂B₉H₉]²⁻ Dicarbollide Ligands

by Ivan D. Grishin, Anastasiya M. Zimina, Sergey A. Anufriev, Nadezhda A. Knyazeva, Alexander V. Piskunov, Fedor M. Dolgushin and Igor B. Sivaev

Catalysts 2021, 11(11), 1409; https://doi.org/10.3390/catal11111409 - 21 Nov 2021

Cited by 9 | Viewed by 1693

Abstract

The effect of methyl substituents in the lower belt of dicarbollide ligands on the redox potential of ruthenacarboranes based thereof, as well as the ability of the metallacarboranes obtained to catalyze radical polymerization with atom transfer were studied. For this purpose, a new [...] Read more.

The effect of methyl substituents in the lower belt of dicarbollide ligands on the redox potential of ruthenacarboranes based thereof, as well as the ability of the metallacarboranes obtained to catalyze radical polymerization with atom transfer were studied. For this purpose, a new approach to the synthesis of closo-ruthenacarboranes based on substituted dicarbollide ligands was developed and six new complexes 3,3-(Ph₂P(CH₂)₄PPh₂)-3-H-3-Cl-9-Me-12-X-closo-3,1,2-RuC₂B₉H₉, 3,3,8-(Ph₂P(CH₂)₄PPh-μ-(C₆H₄-o))-3-Cl-9-Me-12-X-closo-3,1,2-RuC₂B₉H₈ and 3,3,4,8-(Ph₂P(CH₂)₄P-μ-(C₆H₄-o)₂)-3-Cl-9-Me-9-X-closo-3,1,2-RuC₂B₉H₇ (X = H, Me) were synthetized and characterized by single crystal X-ray diffraction, NMR and ESR spectroscopy and MALDI TOF mass-spectrometry. Comparison of the values of the redox potentials of the synthesized ruthenium complexes in 1,2-dichloroethane with the values previously found for the corresponding ruthenacarboranes based on the parent dicarbollide anion showed that the introduction of methyl substituents into the carborane cage led to a decrease in the redox potentials of the complexes, which made them more preferable catalysts for ATRP. Test experiments on the polymerization of MMA showed that the synthesized ruthenacarboranes were effective catalysts for ATRP, the most active being the complex with two methyl groups and two ortho-phenylenecycloboronated fragments. Full article

(This article belongs to the Special Issue Late Transition Metal Complexes: Catalytic and/or Biological Activities)

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15 pages, 4695 KiB

Open AccessArticle

Halide-Doping Effect of Strontium Cobalt Oxide Electrocatalyst and the Induced Activity for Oxygen Evolution in an Alkaline Solution

by Mohamed A. Ghanem, Mabrook S. Amer, Abdullah M. Al-Mayouf, Prabhakarn Arunachalam and Mark T. Weller

Catalysts 2021, 11(11), 1408; https://doi.org/10.3390/catal11111408 - 20 Nov 2021

Cited by 7 | Viewed by 2524

Abstract

Perovskites of strontium cobalt oxyhalides having the chemical formulae Sr₂CoO_4-xH_x (H = F, Cl, and Br; x = 0 and 1) were prepared using a solid-phase synthesis approach and comparatively evaluated as electrocatalysts for oxygen evolution in an [...] Read more.

Perovskites of strontium cobalt oxyhalides having the chemical formulae Sr₂CoO_4-xH_x (H = F, Cl, and Br; x = 0 and 1) were prepared using a solid-phase synthesis approach and comparatively evaluated as electrocatalysts for oxygen evolution in an alkaline solution. The perovskite electrocatalyst crystal phase, surface morphology, and composition were examined by X-ray diffraction, a scanning electron microscope, and energy-dispersive X-ray (EDX) mapping. The electrochemical investigations of the oxyhalides catalysts showed that the doping of F, Cl, or Br into the Sr₂CoO₄ parent oxide enhances the electrocatalytic activity for the oxygen evolution reaction (OER) with the onset potential as well as the potential required to achieve a current density of 10 mA/cm² shifting to lower potential values in the order of Sr₂CoO₄ (1.64, 1.73) > Sr₂CoO₃Br (1.61, 1.65) > Sr₂CoO₃Cl (1.53, 1.60) > Sr₂CoO₃F (1.50, 1.56) V vs. HRE which indicates that Sr₂CoO₃F is the most active electrode among the studied catalysts under static and steady-state conditions. Moreover, Sr₂CoO₃F demonstrates long-term stability and remarkably less charge transfer resistance (R_ct = 36.8 ohm) than the other oxyhalide counterparts during the OER. The doping of the perovskites with halide ions particularly the fluoride-ion enhances the surface oxygen vacancy density due to electron withdrawal away from the Co-atom which improves the ionic and electronic conductivity as well as the electrochemical activity of the oxygen evolution in alkaline solution. Full article

(This article belongs to the Special Issue Advancements in Electrochemical Energy Catalysts)

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24 pages, 9909 KiB

Open AccessFeature PaperArticle

A 5-(2-Pyridyl)tetrazolate Complex of Molybdenum(VI), Its Structure, and Transformation to a Molybdenum Oxide-Based Hybrid Heterogeneous Catalyst for the Epoxidation of Olefins

by Martinique S. Nunes, Diana M. Gomes, Ana C. Gomes, Patrícia Neves, Ricardo F. Mendes, Filipe A. Almeida Paz, André D. Lopes, Anabela A. Valente, Isabel S. Gonçalves and Martyn Pillinger

Catalysts 2021, 11(11), 1407; https://doi.org/10.3390/catal11111407 - 20 Nov 2021

Cited by 9 | Viewed by 3324

Abstract

There is a considerable practical interest in discovering new ways to obtain organomolybdenum heterogeneous catalysts for olefin epoxidation that are easier to recover and reuse and display enhanced productivity. In this study, the complex salt (H₂pytz)[MoO₂Cl₂(pytz)] ( [...] Read more.

There is a considerable practical interest in discovering new ways to obtain organomolybdenum heterogeneous catalysts for olefin epoxidation that are easier to recover and reuse and display enhanced productivity. In this study, the complex salt (H₂pytz)[MoO₂Cl₂(pytz)] (1) (Hpytz = 5-(2-pyridyl)tetrazole) has been prepared, structurally characterized, and employed as a precursor for the hydrolysis-based synthesis of a microcrystalline molybdenum oxide/organic hybrid material formulated as [MoO₃(Hpytz)] (2). In addition to single-crystal X-ray diffraction (for 1), compounds 1 and 2 were characterized by FT-IR and Raman spectroscopies, solid-state ¹³C{¹H} cross-polarization (CP) magic-angle spinning (MAS) NMR, and scanning electron microscopy (SEM). Compounds 1 and 2 were evaluated as olefin epoxidation catalysts using the model reaction of cis-cyclooctene (Cy8) with tert-butyl hydroperoxide (TBHP), at 70 °C, which gave 100% epoxide selectivity up to 100% conversion. While 1 behaved as a homogeneous catalyst, hybrid 2 behaved as a heterogeneous catalyst and could be recovered for recycling without showing structural degradation or loss of catalytic performance over consecutive reaction cycles. The substrate scope was broadened to monoterpene DL-limonene (Lim) and biobased unsaturated fatty acid methyl esters, methyl oleate (MeOle), and methyl linoleate (MeLin), which gave predominantly epoxide products. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Molecular Catalysis)

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15 pages, 3540 KiB

Open AccessArticle

Au-Ag/TiO₂ Thin Films Preparation by Laser Ablation and Sputtering Plasmas for Its Potential Use as Photoanodes in Electrochemical Advanced Oxidation Processes (EAOP)

by Luis Alejandro Martínez-Chávez, Eric Mauricio Rivera-Muñoz, Rodrigo Rafael Velázquez-Castillo, Luis Escobar-Alarcón and Karen Esquivel

Catalysts 2021, 11(11), 1406; https://doi.org/10.3390/catal11111406 - 20 Nov 2021

Cited by 9 | Viewed by 2242

Abstract

Titanium dioxide (TiO₂) is widely used, studied, and synthesized using different methodologies. By a modification of the material, it can be applied to wastewater treatment. A combined sputtering-laser ablation setup was used to deposit TiO₂ thin films modified, individually and [...] Read more.

Titanium dioxide (TiO₂) is widely used, studied, and synthesized using different methodologies. By a modification of the material, it can be applied to wastewater treatment. A combined sputtering-laser ablation setup was used to deposit TiO₂ thin films modified, individually and simultaneously, with gold (Au) and silver (Ag). To investigate the effect of the metal incorporation in titanium and its impact on the photocatalytic activity, with dye discoloration as a pollutant compound model, the deposited films were characterized by UV–Vis, photoluminescence, and Raman spectroscopies, as well as by parallel beam X-ray diffraction. The results showed that films with different Au and Ag loads, and an 18 nm average crystallite size, were obtained. These metals have an essential effect on the deposited film’s compositional, structural, and optical properties, directly reflected in its photocatalytic activity. The photocatalytic test results using UV-Vis showed that, after 1 h of applying a 4.8 V electric voltage, a discoloration of up to 80% of malachite green (MG) was achieved, using ultraviolet (UV) light. Full article

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

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22 pages, 4625 KiB

Open AccessFeature PaperArticle

Use of NaNO₃/SiAl as Heterogeneous Catalyst for Fatty Acid Methyl Ester Production from Rapeseed Oil

by José María Encinar, Juan Félix González, Gloria Martínez and Sergio Nogales-Delgado

Catalysts 2021, 11(11), 1405; https://doi.org/10.3390/catal11111405 - 20 Nov 2021

Cited by 5 | Viewed by 1997

Abstract

The use of heterogeneous catalysts to produce fatty acid methyl esters (FAME) through transesterification with methanol might contribute to both green chemistry and a circular economy, as the process can be simplified, not requiring additional stages to recover the catalyst once the reaction [...] Read more.

The use of heterogeneous catalysts to produce fatty acid methyl esters (FAME) through transesterification with methanol might contribute to both green chemistry and a circular economy, as the process can be simplified, not requiring additional stages to recover the catalyst once the reaction takes place. For this purpose, different catalysts are used, including a wide range of possibilities. In this research the use of NaNO₃/SiAl as a heterogeneous catalyst for FAME production through transesterification of rapeseed oil with methanol is considered. A thorough characterization of the catalyst (including XDR and XPS analysis, SEM microscopy, lixiviation and reusability tests, among others), specific optimization of transesterification by using the final catalyst (considering catalyst amount, stirring rate, methanol/oil ratio, and temperature), and quality determination of the final biodiesel (following the UNE-EN 14214 standard) were carried out. In conclusion, 20 mmol_Na·g_support⁻¹ (that is, NaNO₃/SiAl 20/1) offered the best results, with a high activity (exceeding 99% w/w of FAMEs) without requiring higher impregnation amounts. The best chemical conditions for this heterogeneous catalyst were 5% w/w catalyst, 700 rpm, 9:1 methanol/oil ratio, and 65 °C, obtaining E_a = 73.3 kJ·mol⁻¹ and a high-quality biodiesel, similar to those obtained through homogeneous catalysis. Consequently, this catalyst could be a suitable precursor for FAME production. Full article

(This article belongs to the Special Issue Catalysts in Sustainable, Industrial Processes in Biorefinery and Bioeconomy)

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16 pages, 4927 KiB

Open AccessFeature PaperArticle

Hybrids of Reduced Graphene Oxide Aerogel and CNT for Electrochemical O₂ Reduction

by Javier Hernández-Ferrer, Ana M. Benito, Wolfgang K. Maser and Enrique García-Bordejé

Catalysts 2021, 11(11), 1404; https://doi.org/10.3390/catal11111404 - 20 Nov 2021

Cited by 3 | Viewed by 1852

Abstract

Carbon nanotubes (CNTs), graphene aerogels (GAs), and their hybrid (CNT-GA) prepared by hydrothermal treatment were tested in the electrocatalytic oxygen reduction reaction (ORR). The importance of porous structure derived from the combination of mesoporosity coming from CNTs with macroporosity stemming from GAs was [...] Read more.

Carbon nanotubes (CNTs), graphene aerogels (GAs), and their hybrid (CNT-GA) prepared by hydrothermal treatment were tested in the electrocatalytic oxygen reduction reaction (ORR). The importance of porous structure derived from the combination of mesoporosity coming from CNTs with macroporosity stemming from GAs was evidenced because the hybrid carbon material exhibited synergistic performance in terms of kinetic current and onset potential. Different electrocatalysts were prepared based on these hybrids doped with nitrogen using different precursors and also supporting Fe nanoparticles. N-doped carbon hybrids showed higher electrocatalytic activity than their undoped counterparts. Nevertheless, both doped and undoped materials provided a mixed two and four electron reduction. On the other hand, the addition of a Fe precursor and phenanthroline to the CNT-GA allowed preparing an N-doped hybrid containing Fe nanoparticles which favored the 4-electron oxygen reduction to water, thus being an excellent candidate as a structured cathode in fuel cells. Full article

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

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11 pages, 3039 KiB

Open AccessArticle

Separable Magnetic Fe₃O₄@MoS₂ Composite for Adsorption and Piezo-Catalytic Degradation of Dye

by Chi Zhou, Wencheng Liu, Hanqing Li, Miao Yang and Zixin Yang

Catalysts 2021, 11(11), 1403; https://doi.org/10.3390/catal11111403 - 20 Nov 2021

Cited by 11 | Viewed by 2608

Abstract

Well-designed composite catalysts are of increasing concern due to their improved performance compared to individual components. Herein, we designed and synthesized an Fe₃O₄@MoS₂ composite via a simple hydrothermal method. As for the resultant composite, the MoS₂ nanolayers [...] Read more.

Well-designed composite catalysts are of increasing concern due to their improved performance compared to individual components. Herein, we designed and synthesized an Fe₃O₄@MoS₂ composite via a simple hydrothermal method. As for the resultant composite, the MoS₂ nanolayers presented a novel piezo-catalytic effect, while the Fe₃O₄ core provided a magnetic separation property. The structure and properties of Fe₃O₄@MoS₂ were determined by relevant experiments. It was found that Fe₃O₄@MoS₂ exhibited enhanced piezo-catalytic degradation of rhodamine B and good magnetic recovery/recycling features. The k_obs for rhodamine B degradation over Fe₃O₄@MoS₂ was 0.019 min⁻¹—a little longer than that over MoS₂ (0.013 min⁻¹). Moreover, Fe₃O₄@MoS₂ also showed a favorable ability to adsorb rhodamine B in solution, with a saturation adsorption of 26.8 mg/g. Further studies revealed that piezo-electrons, holes, and superoxide anions were key species in the piezo-catalytic degradation of rhodamine B. Notably, the step where oxygen trapped electrons to produce superoxide anions had a significant impact on the degradation of the dye. This work, not limited to the development of a high-performance MoS₂-based piezo-catalyst, is expected to provide new insights into the working mechanisms and process profiles of composite piezo-catalysts. Full article

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17 pages, 3644 KiB

Open AccessArticle

Epoxidation of 1,5,9-Cyclododecatriene with Hydrogen Peroxide over Ti-MCM-41 Catalyst

by Agnieszka Wróblewska, Marcin Kujbida, Grzegorz Lewandowski, Adrianna Kamińska, Zvi C. Koren and Beata Michalkiewicz

Catalysts 2021, 11(11), 1402; https://doi.org/10.3390/catal11111402 - 19 Nov 2021

Cited by 3 | Viewed by 1499

Abstract

This work presents the results of our research on the epoxidation of 1,5,9-cyclododecatriene (CDT) with hydrogen peroxide over the Ti-MCM-41 catalyst. The influence of the following parameters on the course of the process was investigated: temperature, CDT:H₂O₂ molar ratio, solvent [...] Read more.

This work presents the results of our research on the epoxidation of 1,5,9-cyclododecatriene (CDT) with hydrogen peroxide over the Ti-MCM-41 catalyst. The influence of the following parameters on the course of the process was investigated: temperature, CDT:H₂O₂ molar ratio, solvent composition and its type, and catalyst content. The highest selectivity of CDT transformation to 1,2-epoxy-5,9-cyclododecadiene (ECDD)—approximately 100 mol%, the highest yet reported—was obtained at the CDT conversion of 13 mol% and with the following parameter values: a catalyst content of 5 wt%; a molar ratio of CDT:H₂O₂ = 2; isopropyl alcohol (i-PrOH) as the solvent, with a composition of 80 wt% in the reaction mixture; a temperature of 80 °C; and a reaction time of 240 min. The highest conversion of CDT (37 mol%) was obtained at the ECDD selectivity of 56 mol% and using the following process parameters: a catalyst content of 5 wt%; a molar ratio of CDT:H₂O₂ = 0.5; i-PrOH used as the solvent, with solvent composition of 80 wt%; a temperature of 80 °C; and a reaction time of 60 min. It should be emphasized that the CDT conversion obtained in the current study is higher (by 9 mol%) than that described in the literature on heterogeneous catalysts. Full article

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

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20 pages, 8615 KiB

Open AccessFeature PaperArticle

Oxy-Steam Reforming of Liquefied Natural Gas (LNG) on Mono- and Bimetallic (Ag, Pt, Pd or Ru)/Ni Catalysts

by Pawel Mierczynski, Magdalena Mosinska, Waldemar Maniukiewicz, Krasimir Vasilev and Malgorzata Iwona Szynkowska-Jozwik

Catalysts 2021, 11(11), 1401; https://doi.org/10.3390/catal11111401 - 19 Nov 2021

Cited by 4 | Viewed by 2279

Abstract

This work presents, for the first time, the comparative physicochemical and reactivity studies of a range of bimetallic Pt-Ni, Pd-Ni, Ru-Ni, and Ag-Ni catalysts in the oxy-steam reforming (OSR) of liquefied natural gas (LNG) reaction towards hydrogen generation. In order to achieve the [...] Read more.

This work presents, for the first time, the comparative physicochemical and reactivity studies of a range of bimetallic Pt-Ni, Pd-Ni, Ru-Ni, and Ag-Ni catalysts in the oxy-steam reforming (OSR) of liquefied natural gas (LNG) reaction towards hydrogen generation. In order to achieve the intended purpose of this work, a binary oxide CeO₂·ZrO₂ (1:2) support was prepared via a co-precipitation method. The catalysts’ physicochemical properties were studied using X-ray diffraction (XRD), BET, TPR-H₂, TPD-NH₃, SEM-EDS and XPS methods. The highest activity in the studied process was exhibited by the 1%Pt-5%Ni catalyst supported on CeO₂·ZrO₂ (1:2) system. The highest activity of this system is explained by the specific interactions occurring between the components of the active phase and between the components of the active phase and the carrier itself. The activity results showed that this catalytic system exhibited above 71% of the methane conversion at 600 °C and 60% yield of hydrogen formation. The results of this work demonstrate that the Pt-Ni and Ru-Ni catalytic systems hold promise to be applied in the production of hydrogen to power solid oxide fuel cells. Full article

(This article belongs to the Special Issue Recent Advances in Nickel-Based Catalysts)

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12 pages, 3811 KiB

Open AccessArticle

An Effective Strategy to Enhance the Electrocatalytic Activity of Ruddlesden−Popper Oxides Sr₃Fe₂O₇₋_δ Electrodes for Solid Oxide Fuel Cells

by Longsheng Peng, Qiang Li, Liping Sun and Hui Zhao

Catalysts 2021, 11(11), 1400; https://doi.org/10.3390/catal11111400 - 18 Nov 2021

Cited by 7 | Viewed by 2051

Abstract

The target of this work is to develop advanced electrode materials with excellent performance compared to conventional cathodes. Cobalt-free Ruddlesden−Popper oxides Sr₃Fe_2−xCu_xO₇₋_δ (SFCx, x = 0, 0.1, 0.2) were successfully synthesized and [...] Read more.

The target of this work is to develop advanced electrode materials with excellent performance compared to conventional cathodes. Cobalt-free Ruddlesden−Popper oxides Sr₃Fe_2−xCu_xO₇₋_δ (SFCx, x = 0, 0.1, 0.2) were successfully synthesized and assessed as cathode materials for solid oxide fuel cells (SOFCs). Herein, a Cu-doping strategy is shown to increase the electrical conductivity and improve the electrochemical performance of the pristine Sr₃Fe₂O₇₋_δ. Among all the cathode materials, the Sr₃Fe_1.9Cu_0.1O₇₋_δ (SFC10) cathode exhibits the best electrocatalytic activity for oxygen reduction reaction (ORR). The polarization resistance is 0.11 Ω cm² and the peak power density of the single-cell with an SFC10 cathode reaches 955 mW cm⁻² at 700 °C, a measurement comparable to cobalt-based electrodes. The excellent performance is owed to favorable oxygen surface exchange capabilities and larger oxygen vacancy concentrations at elevated temperatures. Moreover, the electrochemical impedance spectra and distribution of relaxation time results indicate that the charge transfer process at the triple-phase boundary is the rate-limiting step for ORR on the electrode. This work provides an effective strategy for designing novel cathode electrocatalysts for SOFCs. Full article

(This article belongs to the Special Issue Frontiers in Electrocatalysis: Oxygen Reduction, Oxygen Evolution, and Hydrogen Evolution Reactions)

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20 pages, 5005 KiB

Open AccessFeature PaperArticle

New Insight into the Interplay of Method of Deposition, Chemical State of Pd, Oxygen Storage Capability and Catalytic Activity of Pd-Containing Perovskite Catalysts for Combustion of Methane

by Silva Stanchovska, Georgy Ivanov, Sonya Harizanova, Krasimir Tenchev, Ekaterina Zhecheva, Anton Naydenov and Radostina Stoyanova

Catalysts 2021, 11(11), 1399; https://doi.org/10.3390/catal11111399 - 18 Nov 2021

Cited by 1 | Viewed by 1658

Abstract

Elaboration of Pd-supported catalysts for catalytic combustion is, nowadays, considered as an imperative task to reduce the emissions of methane. This study provides new insight into the method of deposition, chemical state of Pd and oxygen storage capability of transition metal ions and [...] Read more.

Elaboration of Pd-supported catalysts for catalytic combustion is, nowadays, considered as an imperative task to reduce the emissions of methane. This study provides new insight into the method of deposition, chemical state of Pd and oxygen storage capability of transition metal ions and their effects on the catalytic reactivity of supported catalysts for the combustion of methane. The catalyst with nominal composition La(Co_0.8Ni_0.1Fe_0.1)_0.85Pd_0.15O₃ was supported on SiO₂-modified/γ-alumina using two synthetic procedures: (i) aerosol assisted chemical vapor deposition (U-AACVD) and (ii) wet impregnation (Imp). A comparative analysis shows that a higher catalytic activity is established for supported catalyst obtained by wet impregnation, where the PdO-like phase is well dispersed and the transition metal ions display a high oxygen storage capability. The reaction pathway over both catalysts proceeds most probably through Mars–van Krevelen mechanism. The supported catalysts are thermally stable when they are aged at 505 °C for 120 h in air containing 1.2 vol.% water vapor. Furthermore, the experimentally obtained data on La(Co_0.8Ni_0.1Fe_0.1)_0.85Pd_0.15O₃—based catalyst, supported on monolithic substrate VDM^®Aluchrom Y Hf are simulated by using a two-dimensional heterogeneous model for monolithic reactor in order to predict the performance of an industrial catalytic reactor for abatement of methane emissions. Full article

(This article belongs to the Special Issue Kinetics and Mechanism of Catalytic Reactions—Integrity of Experiment and Theory)

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20 pages, 3867 KiB

Open AccessArticle

Effect of Adding Chelating Ligands on the Catalytic Performance of Rh-Promoted MoS₂ in the Hydrodesulfurization of Dibenzothiophene

by Siphumelele Majodina, Zenixole R. Tshentu and Adeniyi S. Ogunlaja

Catalysts 2021, 11(11), 1398; https://doi.org/10.3390/catal11111398 - 18 Nov 2021

Cited by 3 | Viewed by 2011

Abstract

Hydrodesulfurization (HDS) is a widely used process currently employed in petroleum refineries to eliminate organosulfur compounds in fuels. The current hydrotreating process struggles to remove organosulfur compounds with a steric hindrance due to the electronic nature of the current catalysts employed. In this [...] Read more.

Hydrodesulfurization (HDS) is a widely used process currently employed in petroleum refineries to eliminate organosulfur compounds in fuels. The current hydrotreating process struggles to remove organosulfur compounds with a steric hindrance due to the electronic nature of the current catalysts employed. In this work, the effects of adding chelating ligands such as ethylenediaminetetraacetic acid (EDTA), citric acid (CA) and acetic acid (AA) to rhodium (Rh) and active molybdenum (Mo) species for dibenzothiophene (DBT) HDS catalytic activity was evaluated. HDS activities followed the order of RhMo/ɣ-Al₂O₃ (88%) > RhMo-AA/ɣ-Al₂O₃ (73%) > RhMo-CA/ɣ-Al₂O₃ (72%) > RhMo-EDTA/ɣ-Al₂O₃ (68%). The observed trend was attributed to the different chelating ligands with varying electronic properties, thus influencing the metal–support interaction and the favorable reduction of the Mo species. RhMo/ɣ-Al₂O₃ offered the highest HDS activity due to its (i) lower metal–support interaction energy, as observed from the RhMo/ɣ-Al₂O₃ band gap of 3.779 eV and the slight shift toward the lower BE of Mo 3d, (ii) increased Mo-O-Mo species (N_Mo-O-Mo ~1.975) and (iii) better sulfidation of Rh and MoO in RhMo/ɣ-Al₂O₃ compared to the chelated catalysts. The obtained data provides that HDS catalytic activity was mainly driven by the structural nature of the RhMo-based catalyst, which influences the formation of more active sites that can enhance the HDS activity. Full article

(This article belongs to the Special Issue Frontiers in Heterogeneous Catalysts for Desulfurization of Fuel Oil)

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16 pages, 7805 KiB

Open AccessFeature PaperArticle

Manganese Molybdenum Oxide Micro Rods Adorned Porous Carbon Hybrid Electrocatalyst for Electrochemical Determination of Furazolidone in Environmental Fluids

by Sivakumar Musuvadhi Babulal, Tse-Wei Chen, Shen-Ming Chen, Wedad A. Al-Onazi and Amal M. Al-Mohaimeed

Catalysts 2021, 11(11), 1397; https://doi.org/10.3390/catal11111397 - 18 Nov 2021

Cited by 4 | Viewed by 2154

Abstract

The frequent occurrence of furazolidone (FZD) in environmental fluids reveals the ongoing increase in use and raises concerns about the need of monitoring it. To investigate the electrochemical behavior of FZD, a novel sensor of manganese molybdenum oxide (MMO) micro rods adorned three-dimensional [...] Read more.

The frequent occurrence of furazolidone (FZD) in environmental fluids reveals the ongoing increase in use and raises concerns about the need of monitoring it. To investigate the electrochemical behavior of FZD, a novel sensor of manganese molybdenum oxide (MMO) micro rods adorned three-dimensional porous carbon (PC) electrocatalyst was constructed. The crystalline structure and surface morphology of the MMO/PC composite was characterized by XRD, Raman, FESEM, and HR-TEM. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and amperometric(i-t) methods were used to assess the electrocatalytic activity of modified electrodes. In the presence of FZD, the as-fabricated MMO/PC modified glassy carbon electrode (GCE) performed better at lower potentials with a greater peak current than other modified GCE. These results emanate from the synergistic effect of the MMO/PC suspension on the GCE. The electrochemical behavior of the amperometric(i-t) technique was used to determine FZD. Amperometric(i-t) detection yielded linear dynamic ranges of 150 nM to 41.05 µM and 41.05 to 471.05 µM with detection limits of 30 nM. The MMO/PC hybrid sensor was also effectively used to detect FZD in environmental fluids, yielding ultra-trace level detection. Full article

(This article belongs to the Special Issue Transition Metals/Oxides/Oxyanions Based Catalysts for Photo-/Electro-Chemical Application)

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16 pages, 6480 KiB

Open AccessArticle

Influence of Synthesis Approach on Controlled Microstructures and Photocatalytic Properties of Ag/AgBr-Activated Carbon Composites on Visible Light Degradation of Tetracycline

by Saheed O. Sanni, Hendrik G. Brink and Elvera L. Viljoen

Catalysts 2021, 11(11), 1396; https://doi.org/10.3390/catal11111396 - 18 Nov 2021

Cited by 4 | Viewed by 1748

Abstract

The influence of the synthesis approach (thermal polyol and deposition–precipitation) regarding the dispersion of Ag/AgBr nanoparticles dispersed on activated carbon prepared from chemical impregnated pinecone (TP-AABR-ACK, and DP-AABR-ACK) was studied, to increase their photocatalytic efficiency on the degradation of tetracycline (TC). The physicochemical [...] Read more.

The influence of the synthesis approach (thermal polyol and deposition–precipitation) regarding the dispersion of Ag/AgBr nanoparticles dispersed on activated carbon prepared from chemical impregnated pinecone (TP-AABR-ACK, and DP-AABR-ACK) was studied, to increase their photocatalytic efficiency on the degradation of tetracycline (TC). The physicochemical characterization evidenced the significance of the ACK catalyst promoter in enhancing controlled microstructures (morphologies and particle size distributions), synergistic interface interaction between AABR NPs and the carbonaceous support, and efficient photogenerated charge carriers separation within TP-AABR-ACK, and DP-AABR-ACK composites. The results revealed 92% removal of TC within 180 min under the LED visible light irradiation, which was achieved using TP-AABR-ACK when compared to DP-AABR-ACK composite and other catalysts in this study. Such superior results achieved with TP-AABR-ACK composite were attributed to controlled morphologies, reduced particle size and agglomeration, improved absorptivity, and superior cooperative effect between the AABR and ACK catalyst promoter as evidenced from SEM, EDX, TEM, UV-DRS, and electrochemical characterizations, respectively. Furthermore, enhanced TOC removal and abundance of reactive superoxide anion generation were achieved with the TP-AABR-ACK composite in this study. Full article

(This article belongs to the Special Issue Structured Semiconductors in Photocatalysis)

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20 pages, 13509 KiB

Open AccessFeature PaperReview

Recent Advances in the Brønsted/Lewis Acid Catalyzed Conversion of Glucose to HMF and Lactic Acid: Pathways toward Bio-Based Plastics

by Cristina Megías-Sayago, Sara Navarro-Jaén, Fabien Drault and Svetlana Ivanova

Catalysts 2021, 11(11), 1395; https://doi.org/10.3390/catal11111395 - 18 Nov 2021

Cited by 22 | Viewed by 4024

Abstract

One of the most trending topics in catalysis recently is the use of renewable sources and/or non-waste technologies to generate products with high added value. That is why, the present review resumes the advances in catalyst design for biomass chemical valorization. The variety [...] Read more.

One of the most trending topics in catalysis recently is the use of renewable sources and/or non-waste technologies to generate products with high added value. That is why, the present review resumes the advances in catalyst design for biomass chemical valorization. The variety of involved reactions and functionality of obtained molecules requires the use of multifunctional catalyst able to increase the efficiency and selectivity of the selected process. The use of glucose as platform molecule is proposed here and its use as starting point for biobased plastics production is revised with special attention paid to the proposed tandem Bronsted/Lewis acid catalysts. Full article

(This article belongs to the Special Issue New Trends in Efficient Brønsted/Lewis Acid Catalysts for Biomass Conversion)

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44 pages, 11933 KiB

Open AccessFeature PaperReview

Recent Progress on Transition Metal Based Layered Double Hydroxides Tailored for Oxygen Electrode Reactions

by Jing Wang, Heng Kong, Haihong Zhong, Yu Jiang, Fei Guo, Nicolas Alonso-Vante and Yongjun Feng

Catalysts 2021, 11(11), 1394; https://doi.org/10.3390/catal11111394 - 18 Nov 2021

Cited by 9 | Viewed by 3874

Abstract

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), namely, so-called oxygen electrode reactions, are two fundamental half-cell reactions in the energy storage and conversion devices, e.g., zinc–air batteries and fuel cells. However, the oxygen electrode reactions suffer from sluggish kinetics, large [...] Read more.

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), namely, so-called oxygen electrode reactions, are two fundamental half-cell reactions in the energy storage and conversion devices, e.g., zinc–air batteries and fuel cells. However, the oxygen electrode reactions suffer from sluggish kinetics, large overpotential and complicated reaction paths, and thus require efficient and stable electrocatalysts. Transition-metal-based layered double hydroxides (LDHs) and their derivatives have displayed excellent catalytic performance, suggesting a major contribution to accelerate electrochemical reactions. The rational regulation of electronic structure, defects, and coordination environment of active sites via various functionalized strategies, including tuning the chemical composition, structural architecture, and topotactic transformation process of LDHs precursors, has a great influence on the resulting electrocatalytic behavior. In addition, an in-depth understanding of the structural performance and chemical-composition-performance relationships of LDHs-based electrocatalysts can promote further rational design and optimization of high-performance electrocatalysts. Finally, prospects for the design of efficient and stable LDHs-based materials, for mass-production and large-scale application in practice, are discussed. Full article

(This article belongs to the Special Issue Transition Metal Catalysis)

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12 pages, 2730 KiB

Open AccessArticle

A Study on the Applicability of NiFe₂O₄ Nanoparticles as the Basis of Catalysts for the Purification of Aqueous Media from Pollutants

by Artem L. Kozlovskiy, Anna S. Zagrebova, Rauan Sh. Abdinov, Inesh E. Kenzhina and Maxim V. Zdorovets

Catalysts 2021, 11(11), 1393; https://doi.org/10.3390/catal11111393 - 18 Nov 2021

Cited by 1 | Viewed by 1469

Abstract

The aim of this work is to evaluate the application of NiFe₂O₄ nanoparticles with spinel structures as the basis of catalysts for the purification of aqueous media from pollutants such as manganese and arsenic. The interest in these catalysts is [...] Read more.

The aim of this work is to evaluate the application of NiFe₂O₄ nanoparticles with spinel structures as the basis of catalysts for the purification of aqueous media from pollutants such as manganese and arsenic. The interest in these catalysts is due to their ease of production and high absorption efficiency, which, together with their magnetic properties, allow the use of nanoparticles for a long time. The sol–gel method, followed by thermal annealing of the samples at different temperatures, was proposed as a method for the synthesis of spinel nanoparticles. The choice of the annealing temperature range of 200–1000 °C is caused by the possibility of estimating changes in the structural properties and the degree of nanoparticles crystallinity. During the study of structural changes in nanoparticles depending on the annealing temperature, it was found that in the temperature range of 200–800 °C, there is an ordering of structural parameters, while for samples obtained at annealing temperatures above 800 °C, there is a partial disorder caused by the agglomeration of nanoparticles with a subsequent increase in their size. According to the results of the studies on the purification of aqueous media from pollutants, it was found that the greatest absorption efficiency belongs to nanoparticles annealed at 500–700 °C, with the purification efficiency of 70–85%, depending on the type of pollutant. The results obtained from the use of nanoparticles as catalysts for the purification of aqueous media show great prospects for their further application on an industrial scale. Full article

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11 pages, 7629 KiB

Open AccessEditor’s ChoiceArticle

Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups

by Yang Li, Xiaoling Lai, Xiaowei Xu, Yat-Ming So, Yijing Du, Zhengze Zhang and Yu Pan

Catalysts 2021, 11(11), 1392; https://doi.org/10.3390/catal11111392 - 18 Nov 2021

Cited by 5 | Viewed by 1934

Abstract

Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, [...] Read more.

Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, (η⁵-C₅Me₅)TiCl₂(O-2,6-ⁱPr₂C₆H₃) (1), (η⁵-C₅Me₅)TiCl₂(N=C^tBu₂) (2) and [Me₂Si(η⁵-C₅Me₄)(N^tBu)]TiCl₂ (3), have been investigated by density functional theory (DFT) method. At the initiation stage, a higher free energy barrier was determined for complex 1, probably due to the presence of electronegative O atom in phenoxy ligand. At the propagation stage, front-side insertion of the second ethylene is kinetically more favorable than back-side insertion for complexes 1 and 2, while both side insertion orientations are comparable for complex 3. The energy decomposition showed that the bridged cyclopentadienyl amide ligand could enhance the rigidity of the active species as suggested by the lowest deformation energy derived from 3. At the chain termination stage, β-H transfer was calculated to be a dominant chain termination route over β-H elimination, presumably owing to the thermodynamic perspective. Full article

(This article belongs to the Special Issue Advances in Ziegler-Natta Type Catalysts for Olefin Polymerization)

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17 pages, 4059 KiB

Open AccessArticle

“Doing More with Less”: Ni(II)@ORMOSIL, a Novel Sol-Gel Pre-Catalyst for the Reduction of Nitrobenzene

by Michael Meistelman, Dan Meyerstein, Ariela Burg, Dror Shamir and Yael Albo

Catalysts 2021, 11(11), 1391; https://doi.org/10.3390/catal11111391 - 18 Nov 2021

Cited by 5 | Viewed by 1976

Abstract

Reduction of nitrobenzene with NaBH₄ using zero-valent iron nanoparticles (ZVI-NPs) and NiCl₂∙6H₂O incorporated in organically modified hybrid silica matrices as ZVI@ORMOSIL and Ni(II)@ORMOSIL catalysts is proposed as a remediation strategy. Ni(II)@ORMOSIL is prepared by ion-exchanging H⁺ of [...] Read more.

Reduction of nitrobenzene with NaBH₄ using zero-valent iron nanoparticles (ZVI-NPs) and NiCl₂∙6H₂O incorporated in organically modified hybrid silica matrices as ZVI@ORMOSIL and Ni(II)@ORMOSIL catalysts is proposed as a remediation strategy. Ni(II)@ORMOSIL is prepared by ion-exchanging H⁺ of the ORMOSIL matrix with Ni^II. Ni(II)@ORMOSIL is a pre-catalyst that undergoes reduction by NaBH₄ by an in-situ reaction and promotes nitrobenzene reduction by the unconsumed NaBH₄, leading to sparing use of the catalyst. Ni(II)@ORMOSIL undergoes color change from green to black in this process, returning to a green hue after washing and drying. Nitrobenzene reductions were examined in aqueous acetonitrile solvent mixtures, and the reduction cascade produced the reaction end-products with catalytic implications. Plausible mechanisms of ZVI@ORMOSIL and Ni(II)@ORMOSIL catalyzed reductions of nitrobenzene are discussed. This work is the first to report M(II)@ORMOSIL pre-catalysts for in-situ reduction of nitrobenzene, and expands the scope of the ORMOSIL series of catalysts for the reduction of polluting compounds. This approach enables the development of catalysts that use very low concentrations of transition metal cations. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Achievements in Electrocatalysis for Sustainable Energy Technologies)

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14 pages, 2745 KiB

Open AccessFeature PaperArticle

Cold-Active Lipase-Based Biocatalysts for Silymarin Valorization through Biocatalytic Acylation of Silybin

by Giulia Roxana Gheorghita, Victoria Ioana Paun, Simona Neagu, Gabriel-Mihai Maria, Madalin Enache, Cristina Purcarea, Vasile I. Parvulescu and Madalina Tudorache

Catalysts 2021, 11(11), 1390; https://doi.org/10.3390/catal11111390 - 17 Nov 2021

Viewed by 1765

Abstract

Extremophilic biocatalysts represent an enhanced solution in various industrial applications. Integrating enzymes with high catalytic potential at low temperatures into production schemes such as cold-pressed silymarin processing not only brings value to the silymarin recovery from biomass residues, but also improves its solubility [...] Read more.

Extremophilic biocatalysts represent an enhanced solution in various industrial applications. Integrating enzymes with high catalytic potential at low temperatures into production schemes such as cold-pressed silymarin processing not only brings value to the silymarin recovery from biomass residues, but also improves its solubility properties for biocatalytic modification. Therefore, a cold-active lipase-mediated biocatalytic system has been developed for silybin acylation with methyl fatty acid esters based on the extracellular protein fractions produced by the psychrophilic bacterial strain Psychrobacter SC65A.3 isolated from Scarisoara Ice Cave (Romania). The extracellular production of the lipase fraction was enhanced by 1% olive-oil-enriched culture media. Through multiple immobilization approaches of the cold-active putative lipases (using carbodiimide, aldehyde-hydrazine, or glutaraldehyde coupling), bio-composites (S1–5) with similar or even higher catalytic activity under cold-active conditions (25 °C) have been synthesized by covalent attachment to nano-/micro-sized magnetic or polymeric resin beads. Characterization methods (e.g., FTIR DRIFT, SEM, enzyme activity) strengthen the biocatalysts’ settlement and potential. Thus, the developed immobilized biocatalysts exhibited between 80 and 128% recovery of the catalytic activity for protein loading in the range 90–99% and this led to an immobilization yield up to 89%. The biocatalytic acylation performance reached a maximum of 67% silybin conversion with methyl decanoate acylating agent and nano-support immobilized lipase biocatalyst. Full article

(This article belongs to the Special Issue Contemporary Solutions for Advanced Catalytic Materials with a High Impact on Society)

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Catalysts, Volume 11, Issue 11 (November 2021) – 163 articles

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