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Catalysts, Volume 11, Issue 3 (March 2021) – 113 articles

Cover Story (view full-size image): The growing world energy consumption with reliance on conventional energy sources and associated environmental pollution are considered the most serious threats faced by mankind. Accordingly, heterogeneous photocatalysis has become one of the most frequently investigated technologies, due to its dual functionality, i.e., environmental remediation and converting solar energy into chemical energy, especially molecular hydrogen. However, the use of a suitable electron donor, in the photocatalytic reforming, is required to achieve acceptable efficiency. As the aromatic compounds, e.g., phenols, polyaromatic hydrocarbons and organic dyes, are widely spread in aquatic environment, they are considered attractive targets to apply this technology. Such pollutants would replace other potentially costly electron donors, achieving dual-functionality, that is, improving the water quality and [...] Read more.
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Open AccessArticle
Investigations on the Ethylene Polymerization with Bisarylimine Pyridine Iron (BIP) Catalysts
Catalysts 2021, 11(3), 407; https://doi.org/10.3390/catal11030407 - 23 Mar 2021
Viewed by 445
Abstract
The kinetics and terminations of ethylene polymerization, mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts, and activated by large amounts of methyl aluminoxane (MAO) was studied. Narrow distributed paraffins from initially formed aluminum polymeryls and broader distributed 1-polyolefins and (bimodal) mixtures, thereof, [...] Read more.
The kinetics and terminations of ethylene polymerization, mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts, and activated by large amounts of methyl aluminoxane (MAO) was studied. Narrow distributed paraffins from initially formed aluminum polymeryls and broader distributed 1-polyolefins and (bimodal) mixtures, thereof, were obtained after acidic workup. The main pathway of olefin formation is beta-hydrogen transfer to ethylene. The rate of polymerization in the initial phase is inversely proportional to the co-catalyst concentration for all pre-catalysts; a first-order dependence was found on ethylene and catalyst concentrations. The inhibition by aluminum alkyls is released to some extent in a second phase, which arises after the original methyl groups are transformed into n-alkyl entities and the aluminum polymeryls partly precipitate in the toluene medium. The catalysis is interpretable in a mechanism, wherein, the relative rate of chain shuttling, beta-hydrogen transfer and insertion of ethylene are determining the outcome. Beta-hydrogen transfer enables catalyst mobility, which leads to a (degenerate) chain growth of already precipitated aluminum alkyls. Stronger Lewis acidic centers of the single site catalysts, and those with smaller ligands, are more prone to yield 1-olefins and to undergo a faster reversible alkyl exchange between aluminum and iron. Full article
(This article belongs to the Special Issue Homogeneous Catalysis with Earth-Abundant Metal Complexes)
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Open AccessArticle
Elucidating the Influence of the d-Band Center on the Synthesis of Isobutanol
Catalysts 2021, 11(3), 406; https://doi.org/10.3390/catal11030406 - 23 Mar 2021
Viewed by 317
Abstract
As the search for carbon-efficient synthesis pathways for green alternatives to fossil fuels continues, an expanding class of catalysts have been developed for the upgrading of lower alcohols. Understanding of the acid base functionalities has greatly influenced the search for new materials, but [...] Read more.
As the search for carbon-efficient synthesis pathways for green alternatives to fossil fuels continues, an expanding class of catalysts have been developed for the upgrading of lower alcohols. Understanding of the acid base functionalities has greatly influenced the search for new materials, but the influence of the metal used in catalysts cannot be explained in a broader sense. We address this herein and correlate our findings with the most fundamental understanding of chemistry to date by applying it to d-band theory as part of an experimental investigation. The commercial catalysts of Pt, Rh, Ru, Cu, Pd, and Ir on carbon as a support have been characterized by means of SEM, EDX-mapping, STEM, XRD, N2-physisorption, and H2-chemisorption. Their catalytic activity has been established by means of c-methylation of ethanol with methanol. For all catalysts, the TOF with respect to i-butanol was examined. The Pt/C reached the highest TOF with a selectivity towards i-butanol of 89%. The trend for the TOFs could be well correlated with the d-band centers of the metal, which formed a volcano curve. Therefore, this study is another step towards the rationalization of catalyst design for the upgrading of alcohols into carbon-neutral fuels or chemical feedstock. Full article
(This article belongs to the Special Issue Engineering Materials for Catalysis)
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Open AccessFeature PaperArticle
Hydrogen Production via Pd-TiO2 Photocatalytic Water Splitting under Near-UV and Visible Light: Analysis of the Reaction Mechanism
Catalysts 2021, 11(3), 405; https://doi.org/10.3390/catal11030405 - 23 Mar 2021
Viewed by 317
Abstract
Photocatalytic hydrogen production via water splitting using a noble metal on a TiO2 is a technology that has developed rapidly over the past few years. Specifically, palladium doped TiO2 irradiated with near-UV or alternatively with visible light has shown promising results. [...] Read more.
Photocatalytic hydrogen production via water splitting using a noble metal on a TiO2 is a technology that has developed rapidly over the past few years. Specifically, palladium doped TiO2 irradiated with near-UV or alternatively with visible light has shown promising results. With this end in mind, strategically designed experiments were developed in the Photo-CREC Water-II (PCW-II) Reactor using a 0.25 wt.% Pd-TiO2 under near-UV and visible light, and ethanol as an organic scavenger. Acetaldehyde, carbon monoxide, carbon dioxide, methane, ethane, ethylene, and hydrogen peroxide together with hydrogen were the main chemical species observed. A Langmuir adsorption isotherm was also established for hydrogen peroxide. On this basis, it is shown that pH variations, hydrogen peroxide formation/adsorption, and the production of various redox chemical species provide an excellent carbon element balance, as well as OH and H radicals balances. Under near-UV irradiation, 113 cm3 STP of H2 is produced after 6 h, reaching an 99.8% elemental carbon balance and 99.2% OH and H and radical balance. It is also proven that a similar reaction network can be considered adequate for the photoreduced Pd-TiO2 photocatalyst yielding 29 cm3 STP of H2 with 95.4% carbon and the 97.5% OH–H radical balance closures. It is shown on this basis that a proposed “series-parallel” reaction network describes the water splitting reaction using the mesoporous Pd-TiO2 and ethanol as organic scavenger. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)
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Open AccessReview
An Overview of Lean Exhaust deNOx Aftertreatment Technologies and NOx Emission Regulations in the European Union
Catalysts 2021, 11(3), 404; https://doi.org/10.3390/catal11030404 - 23 Mar 2021
Viewed by 1058
Abstract
This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more [...] Read more.
This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more restrictions on the permitted pollutant emission levels and new technologies developed in order to meet these restrictions. The review begins first with the American and then European directives promulgated in the 1970s, aimed at limiting emissions of pollutants from road transport vehicles. Particular attention is paid to the introduction of the Euro standards in the European Union for light- and heavy-duty vehicles, used as a legal and time frame reference for the evolution of emission aftertreatment systems (ATSs). The paper also describes governmental approaches implemented for the control of pollutant emissions in circulating vehicles, such as market surveillance and in-service conformity. In parallel, it is explained how the gradual introduction of small-scale devices aimed at the NOx control, such as lean NOx traps (LNTs) systems, and, most of all, the selective catalytic reduction (SCR) of NOx, permitted the application to road-transport vehicles of this ATS, originally designed in larger sizes for industrial usage. The paper reviews chemical processes occurring in SCR systems and their advantages and drawbacks with respect to the pollutant emission limits imposed by the legislation. Their potential side effects are also addressed, such as the emission of extra, not-yet regulated pollutants such as, for example, NH3 and N2O. The NOx, N2O, and NH3 emission level evolution with the various Euro standards for both light- and heavy-duty vehicles are reported in the light of experimental data obtained at the European Commission’s Joint Research Centre. It is observed that the new technologies, boosted by increasingly stricter legal limits, have led in the last two decades to a clear decrease of over one order of magnitude of NOx emissions in Diesel light-duty vehicles, bringing them to the same level as Euro 6 gasoline vehicles (10 mg/km to 20 mg/km in average). On the other hand, an obvious increase in the emissions of both NH3 and N2O is observed in both Diesel and gasoline light-duty vehicles, whereby NH3 emissions in spark-ignition vehicles are mainly linked to two-reaction mechanisms occurring in three-way catalysts after the catalyst light-off and during engine rich-operation. NH3 emissions measured in recent Euro 6 light-duty vehicles amount to a few mg/km for both gasoline and Diesel engines, whereby N2O emissions exceeding a dozen mg/km have been observed in Diesel vehicles only. The present paper can be regarded as part of a general assessment in view of the next EU emission standards, and a discussion on the role the SCR technology may serve as a NOx emission control strategy from lean-burn vehicles. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)
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Open AccessFeature PaperArticle
Modified-TiO2 Photocatalyst Supported on β-SiC Foams for the Elimination of Gaseous Diethyl Sulfide as an Analog for Chemical Warfare Agent: Towards the Development of a Photoreactor Prototype
Catalysts 2021, 11(3), 403; https://doi.org/10.3390/catal11030403 - 23 Mar 2021
Viewed by 265
Abstract
In the context of the increase in chemical threat due to warfare agents, the development of efficient methods for destruction of Chemical Warfare Agents (CWAs) are of first importance both for civilian and military purposes. Amongst possible methods for destruction of CWAs, photocatalytic [...] Read more.
In the context of the increase in chemical threat due to warfare agents, the development of efficient methods for destruction of Chemical Warfare Agents (CWAs) are of first importance both for civilian and military purposes. Amongst possible methods for destruction of CWAs, photocatalytic oxidation is an alternative one. The present paper reports on the preparation of Ta and Sn doped TiO2 photocatalysts immobilized on β-SiC foams for the elimination of diethyl sulfide (DES) used as a model molecule mimicking Yperite (Mustard Gas) in gaseous phase. Photo-oxidation efficiency of doped TiO2 catalyst has been compared with TiO2-P25. Here, we demonstrate that the Sn doped-TiO2 with a Polyethylene glycol (PEG)/TiO2 ratio of 7 exhibits the best initial activity (up to 90%) but is deactivates more quickly than Ta doped-TiO2 (40% after 800 min). The activity of the catalysts is strongly influenced by the adsorption properties of the support, as β-SiC foams adsorb DES and other sulfur compounds. This adsorption makes it possible to limit the poisoning of the catalysts and to maintain an acceptable conversion rate even after ten hours under continuous DES flow. Washing with NaOH completely regenerates the catalyst after a firs treatment and even seems to “wash” it by removing impurities initially present on the foams. Full article
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Open AccessArticle
Photocatalytic Nanocomposite Polymer-TiO2 Membranes for Pollutant Removal from Wastewater
Catalysts 2021, 11(3), 402; https://doi.org/10.3390/catal11030402 - 23 Mar 2021
Viewed by 523
Abstract
Photocatalytic TiO2-PVDF/PMMA nano-composites flat sheet membranes were fabricated by phase inversion and then employed in a crossflow filtration pilot to remove model pollutants of various sizes and charge from aqueous solution. The dope solution contained a mixture of PVDF and PMMA [...] Read more.
Photocatalytic TiO2-PVDF/PMMA nano-composites flat sheet membranes were fabricated by phase inversion and then employed in a crossflow filtration pilot to remove model pollutants of various sizes and charge from aqueous solution. The dope solution contained a mixture of PVDF and PMMA as polymers, polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) as additives, triethyl phosphate (TEP) as green solvent and TiO2 as immobilized photo catalyst. After undergoing characterization tests such as SEM morphology thickness, porosity, contact angle and water permeability, the membranes were used to eliminate the model pollutants from synthetic aqueous solution. The impact of the operating conditions (i.e., pH, pressure and initial pollutant concentration) and composition of the doping solution on the performance and photocatalytic and antifouling activity of the membranes was investigated. The results showed that Congo Red and Tartrazine despite their small size were rejected at 99% and 81%, respectively, because of their negative charge, while Ciprofloxacin, which is larger than Tartrazine but of neutral charge, crossed the membrane. The permeability did not decrease with a decline in pollutant concentration but diminished when the pressure increased and was reduced by more than half for wastewater. Full article
(This article belongs to the Special Issue Photocatalysis in the Wastewater Treatment)
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Open AccessArticle
Synthesis of Novel Heteroleptic Oxothiolate Ni(II) Complexes and Evaluation of Their Catalytic Activity for Hydrogen Evolution
Catalysts 2021, 11(3), 401; https://doi.org/10.3390/catal11030401 - 22 Mar 2021
Viewed by 531
Abstract
Two heteroleptic nickel oxothiolate complexes, namely [Ni(bpy)(mp)] (1) and [Ni(dmbpy)(mp)] (2), where mp = 2-hydroxythiophenol, bpy = 2,2′-bipyridine and dmbpy = 4,4′-dimethyl-2,2′-bipyridine were synthesized and characterized with various physical and spectroscopic methods. Complex 2 was further characterized by single [...] Read more.
Two heteroleptic nickel oxothiolate complexes, namely [Ni(bpy)(mp)] (1) and [Ni(dmbpy)(mp)] (2), where mp = 2-hydroxythiophenol, bpy = 2,2′-bipyridine and dmbpy = 4,4′-dimethyl-2,2′-bipyridine were synthesized and characterized with various physical and spectroscopic methods. Complex 2 was further characterized by single crystal X-ray diffraction data. The complex crystallizes in the monoclinic P 21/c system and in its neutral form. The catalytic properties of both complexes for proton reduction were evaluated with photochemical and electrochemical studies. Two different in their nature photosensitizers, namely fluorescein and CdTe-TGA-coated quantum dots, were tested under various conditions. The role of the electron donating character of the methyl substituents was revealed in the light of the studies. Thus, catalyst 2 performs better than 1, reaching 39.1 TONs vs. 4.63 TONs in 3 h, respectively, in electrochemical experiments. In contrast, complex 1 is more photocatalytically active than 2, achieving a TON of over 6700 in 120 h of irradiation. This observed reverse catalytic activity suggests that HER mechanism follows different pathways in electrocatalysis and photocatalysis. Full article
(This article belongs to the Special Issue Catalytic Hydrogen Production, Storage and Application)
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Open AccessArticle
Photocatalytic Degradation of Polycyclic Aromatic Hydrocarbons in Fine Particulate Matter (PM2.5) Collected on TiO2-Supporting Quartz Fibre Filters
Catalysts 2021, 11(3), 400; https://doi.org/10.3390/catal11030400 - 22 Mar 2021
Viewed by 322
Abstract
Airborne fine particulate matter (PM2.5) pollution is known to have adverse effects on human health, and owing to their carcinogenic and mutagenic nature, polycyclic aromatic hydrocarbons (PAHs) are of particular concern. This study investigated the effect of ultraviolet (UV)-induced photocatalysis on [...] Read more.
Airborne fine particulate matter (PM2.5) pollution is known to have adverse effects on human health, and owing to their carcinogenic and mutagenic nature, polycyclic aromatic hydrocarbons (PAHs) are of particular concern. This study investigated the effect of ultraviolet (UV)-induced photocatalysis on the degradation of PAHs in PM2.5, employing titanium dioxide (TiO2)-supporting quartz fibre filters. A TiO2 layer was formed on the quartz fibre filters, and airborne PM2.5 was collected using an air sample at a flow rate of 500 L/min for 24 h. The PM2.5 samples were subsequently irradiated with ultraviolet rays at 1.1 mW/cm2. The amounts of nine targeted PAHs (phenanthrene, PHE; anthracene, ANT; pyrene, PYR; benzo[a]anthracene, BaA; chrysene, CHR; benzo[b]fluoranthene, BbF; benzo[k]fluoranthene, BkF; benzo[a]pyrene, BaP; and benzo[g,h,i]perylene, BgP) gradually decreased during the treatment, with half-lives ranging from 18 h (PHE) to 3 h (BaP), and a significantly greater reduction was found in comparison with the PAHs collected in the control (non-TiO2 coated) quartz fibre filters. However, the degradation rates were much faster when the PAHs were in direct contact with the TiO2 layer. As PM2.5 is a mixture of various kinds of solids, co-existing components can be a rate-determining factor in the UV-induced degradation of PAHs. This was demonstrated by a remarkable increase in degradation rates following the removal of co-existing salts from the PM2.5 using water treatment. Full article
(This article belongs to the Special Issue NanoBio Hybrids and Photocatalysis)
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Open AccessFeature PaperArticle
Optical Management of CQD/[email protected] Arrays with Highly Efficient Capability of Dye Degradation
Catalysts 2021, 11(3), 399; https://doi.org/10.3390/catal11030399 - 22 Mar 2021
Viewed by 370
Abstract
The facile synthetic method for the preparation of incorporated carbon quantum dots (CQDs)/Ag nanoparticles (AgNPs) with well-aligned silicon nanowire (SiNW) arrays is demonstrated, offering the superior photodegradation capabilities covering UV to visible wavelength regions. By examining the morphology, microstructure, crystallinity, chemical feature, surface [...] Read more.
The facile synthetic method for the preparation of incorporated carbon quantum dots (CQDs)/Ag nanoparticles (AgNPs) with well-aligned silicon nanowire (SiNW) arrays is demonstrated, offering the superior photodegradation capabilities covering UV to visible wavelength regions. By examining the morphology, microstructure, crystallinity, chemical feature, surface groups, light-emitting, and reflection characteristics, these hybrid heterostructures are systematically identified. Moreover, the involving degradation kinetics, band diagram, cycling capability, and underlying mechanism of photodegradation are investigated, validating their remarkable and reliable photocatalytic performances contributed from the strongly reduced light reflectivity, superior capability of charge separation, and sound wettability with dye solutions. Full article
(This article belongs to the Special Issue Photocatalytic Removal of Dyes)
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Open AccessArticle
Improvement of Propylene Epoxidation Caused by Silver Plasmon Excitation by UV-LED Irradiation on a Sodium-Modified Silver Catalyst Supported on Strontium Carbonate
Catalysts 2021, 11(3), 398; https://doi.org/10.3390/catal11030398 - 21 Mar 2021
Viewed by 366
Abstract
The effect that UV-LED irradiation exerted on a sodium-modified silver catalyst supported on strontium carbonate (Ag-Na/SrCO3) was examined during an epoxidation of propylene to propylene oxide. Based on our previous study, we used Ag(56)-Na(1)/SrCO3 in this study. The numbers in [...] Read more.
The effect that UV-LED irradiation exerted on a sodium-modified silver catalyst supported on strontium carbonate (Ag-Na/SrCO3) was examined during an epoxidation of propylene to propylene oxide. Based on our previous study, we used Ag(56)-Na(1)/SrCO3 in this study. The numbers in parentheses refer to the weight percentage of silver and sodium. Although this catalyst system did not contain typical photocatalysts such as titanium oxide or tungsten oxide, UV-LED irradiation of Ag(56)-Na(1)/SrCO3 resulted in an evident improvement in the selectivity and yield of propylene oxide. Such an advantageous effect of UV-LED irradiation could not be discussed based on the bandgap used in photocatalysts and, therefore, we proposed a mechanism based on the plasmon excitation of silver, which could be accomplished using the irradiation wavelength of UV-LED to produce electrons. Since the lifespan of these electrons is expected to be short, it is difficult to place them into direct contact with the gas phase of oxygen. Once the generated electrons move to SrCO3, however, the lifespan is improved, which could allow suitable contact with oxygen in the gas phase to form active oxygen. If the oxygen is active for epoxidation as hydrogen peroxide, this could explain the improvement in activity from UV-LED irradiation. Full article
(This article belongs to the Special Issue Catalytic Epoxidation Reaction)
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Open AccessArticle
The Impact of 3-(trihydroxysilyl)-1-propanesulfonic Acid Treatment on the State of Vanadium Incorporated on SBA-15 Matrix
Catalysts 2021, 11(3), 397; https://doi.org/10.3390/catal11030397 - 21 Mar 2021
Viewed by 339
Abstract
Bifunctional catalysts—e.g., those with acidic and redox sites—are of particular importance, especially in the cascade processes, including the one-pot transformation of glycerol to acrylic acid. In this study, we explore one aspect of the preparation of a vanadium-containing catalyst, which can be further [...] Read more.
Bifunctional catalysts—e.g., those with acidic and redox sites—are of particular importance, especially in the cascade processes, including the one-pot transformation of glycerol to acrylic acid. In this study, we explore one aspect of the preparation of a vanadium-containing catalyst, which can be further modified with 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS). The state of vanadium species loaded on mesoporous ordered silica of SBA-15 type was investigated before and after treatment with TPS, which can also be applied for the generation of acidic centers. Two vanadium sources, i.e., ammonium metavanadate and vanadium(IV) oxide sulfate, were applied to generate redox sites on SBA-15. The structure of materials obtained was analyzed using N2 adsorption/desorption and XRD measurements. For the estimation of the amount of vanadium and characterization of its state, the following techniques were applied: ICP, UV-Vis, XPS, ESR and FTIR combined with pyridine adsorption. The treatment of vanadium containing SBA-15 with TPS was found to lead to the oxidation of V4+ to V5+ and the partial removal of vanadium species, leading to a decrease in the number of penta-coordinated vanadium species. These features should be taken into account in the design of bifunctional catalysts with vanadium-active centers and SO3H acidic sites coming from TPS. Full article
(This article belongs to the Special Issue Catalytic and Electrocatalytic Applications of Nanomaterials)
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Open AccessArticle
Synthesis of Magnetic α-Fe2O3/Rutile TiO2 Hollow Spheres for Visible-Light Photocatalytic Activity
Catalysts 2021, 11(3), 396; https://doi.org/10.3390/catal11030396 - 20 Mar 2021
Viewed by 445
Abstract
The high recombination rate of the electron-hole pair on the surface of rutile TiO2 (RT) reduces its photocatalytic performance, although it has high thermodynamic stability and few internal grain defects. Therefore, it is necessary for RT to develop effective methods to reduce [...] Read more.
The high recombination rate of the electron-hole pair on the surface of rutile TiO2 (RT) reduces its photocatalytic performance, although it has high thermodynamic stability and few internal grain defects. Therefore, it is necessary for RT to develop effective methods to reduce electron-hole pair recombination. In this study, magnetic α-Fe2O3/Rutile TiO2 self-assembled hollow spheres were fabricated via a facile hydrothermal reaction and template-free method. Based on the experimental result, phosphate concentration was found to play a crucial role in controlling the shape of these hollow α-Fe2O3/RT nanospheres, and the optimal concentration is 0.025 mM. Due to a heterojunction between α-Fe2O3 and RT, the electron-hole pair recombination rate was reduced, the as-synthesized hollow α-Fe2O3/RT nanospheres exhibited excellent photocatalysis in rhodamine B (RhB) photodegradation compared to α-Fe2O3 and RT under visible-light irradiation, and the degradation rate was about 16% (RT), 60% (α-Fe2O3), and 93% (α-Fe2O3/RT) after 100 min. Moreover, α-Fe2O3/RT showed paramagnetism and can be recycled to avoid secondary environmental pollution. Full article
(This article belongs to the Section Photocatalysis)
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Open AccessArticle
Photocatalytic Oxygenation of Heterostilbenes—Batch versus Microflow Reactor
Catalysts 2021, 11(3), 395; https://doi.org/10.3390/catal11030395 - 20 Mar 2021
Viewed by 420
Abstract
On the basis of earlier results with furan and thiophene derivatives of benzobicyclo[3.2.1]octadiene, photocatalytic oxygenation of novel furo- and thieno heterostilbenes with water-soluble manganese(III) porphyrins offered suitable possibilities to study their reactivities and reaction pathways depending on the heteroatom and the catalyst charge. [...] Read more.
On the basis of earlier results with furan and thiophene derivatives of benzobicyclo[3.2.1]octadiene, photocatalytic oxygenation of novel furo- and thieno heterostilbenes with water-soluble manganese(III) porphyrins offered suitable possibilities to study their reactivities and reaction pathways depending on the heteroatom and the catalyst charge. The experiments were carried out in two reactors types (batch and microflow) to investigate the geometric effects. NMR spectroscopy, GC, and UPLC/MS analyses were applied for identification and quantification of the products. As our results indicated, the 2-thienyl and the common p-tolyl groups in the starting compounds remained intact due to their stronger aromaticity. Hence, the thieno derivative underwent oxygenation only at the open-chain part of the molecule, and the rates of its reactions were much lower than those of the furyl analogue. The less stable furan ring was easily oxygenated, its products with highest ratios were 2-furanon derivatives. Epoxide formation occurred at the open-chain parts of both substrates preferably by the anionic catalyst. Nevertheless, the conversion rates of the substrates were higher with the cationic porphyrin, according to electrophilic attacks by photogenerated Mn(V)=O species. Additionally, the reactions were significantly faster in microflow reactors due to the more favorable circumstances of mass transfer, diffusion, and light penetration. Full article
(This article belongs to the Special Issue Photocatalytic Synthesis)
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Open AccessArticle
Study on the Development of High-Performance P-Mo-V Catalyst and the Influence of Aldehyde Impurities on Catalytic Performance in Selective Oxidation of Methacrolein to Methacrylic Acid
Catalysts 2021, 11(3), 394; https://doi.org/10.3390/catal11030394 - 19 Mar 2021
Viewed by 307
Abstract
A series of KxH1.1-xCu0.2Cs1(NH4)1.5PVMo11O40 (KxCuCsNH4PVA) catalysts with different x values were synthesized to catalyze the selective oxidation of methacrolein (MAL) to methacrylic acid (MAA). The effects [...] Read more.
A series of KxH1.1-xCu0.2Cs1(NH4)1.5PVMo11O40 (KxCuCsNH4PVA) catalysts with different x values were synthesized to catalyze the selective oxidation of methacrolein (MAL) to methacrylic acid (MAA). The effects of potassium (K) ions on both the structure and catalytic activity were studied in detail. The optimum K0.6CuCsNH4PVA exhibited a large surface area, more acid sites, and abundant active species (V4+/VO2+) in the secondary structure of the Keggin structure, consequently offering good catalytic performance. Furthermore, K ions increased the MAA selectivity at the expense of carbon monoxide and carbon dioxide (together defined as COX). Additionally, several process parameters for MAL oxidation were evaluated in the processing experiments. The effects of aldehyde impurities (formaldehyde and propanal) on the catalytic performance were investigated. Possible detrimental effects (catalyst poisoning and structural damage) of aldehyde impurities were excluded. A light decrease in MAL conversion could be attributed to the competitive adsorption of aldehyde impurities and MAL on the catalyst. Hopefully, this work contributes to the design of stable and feasible catalysts for the industrial production of MAA. Full article
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Open AccessReview
A Review of Hydrogen Purification Technologies for Fuel Cell Vehicles
Catalysts 2021, 11(3), 393; https://doi.org/10.3390/catal11030393 - 19 Mar 2021
Viewed by 371
Abstract
Nowadays, we face a series of global challenges, including the growing depletion of fossil energy, environmental pollution, and global warming. The replacement of coal, petroleum, and natural gas by secondary energy resources is vital for sustainable development. Hydrogen (H2) energy is [...] Read more.
Nowadays, we face a series of global challenges, including the growing depletion of fossil energy, environmental pollution, and global warming. The replacement of coal, petroleum, and natural gas by secondary energy resources is vital for sustainable development. Hydrogen (H2) energy is considered the ultimate energy in the 21st century because of its diverse sources, cleanliness, low carbon emission, flexibility, and high efficiency. H2 fuel cell vehicles are commonly the end-point application of H2 energy. Owing to their zero carbon emission, they are gradually replacing traditional vehicles powered by fossil fuel. As the H2 fuel cell vehicle industry rapidly develops, H2 fuel supply, especially H2 quality, attracts increasing attention. Compared with H2 for industrial use, the H2 purity requirements for fuel cells are not high. Still, the impurity content is strictly controlled since even a low amount of some impurities may irreversibly damage fuel cells’ performance and running life. This paper reviews different versions of current standards concerning H2 for fuel cell vehicles in China and abroad. Furthermore, we analyze the causes and developing trends for the changes in these standards in detail. On the other hand, according to characteristics of H2 for fuel cell vehicles, standard H2 purification technologies, such as pressure swing adsorption (PSA), membrane separation and metal hydride separation, were analyzed, and the latest research progress was reviewed. Full article
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Open AccessFeature PaperArticle
Physico-Chemical Changes in the KCl-MgCl2/La-FAU Composite Catalyst Induced by Oxidative Dehydrogenation of Ethane
Catalysts 2021, 11(3), 392; https://doi.org/10.3390/catal11030392 - 19 Mar 2021
Viewed by 397
Abstract
In this research, a binary eutectic composition of KCl and MgCl2 supported over lanthanum exchanged FAU (faujasite) zeolite has been investigated for the oxidative dehydrogenation (ODH) of ethane. The catalyst was prepared by the thermal treatment of La-FAU with a mechanical mixture [...] Read more.
In this research, a binary eutectic composition of KCl and MgCl2 supported over lanthanum exchanged FAU (faujasite) zeolite has been investigated for the oxidative dehydrogenation (ODH) of ethane. The catalyst was prepared by the thermal treatment of La-FAU with a mechanical mixture of alkali chlorides under a flow of helium at 500 °C. The eutectic mixture of alkali chlorides formed at this temperature and a molten layer were spread over the support. Synthesized fresh and spent catalysts were characterized to obtain information about changes in crystallinity, textural properties, phase content, chemical composition, and morphology of the catalyst over the reaction time. The initial conversion of ethane was 80% with ethene as the main product (65% yield). The catalyst deactivation has been demonstrated over time on the stream (TOS). The characterization methods confirmed that the chlorine was being removed from the catalyst. The side products detected by mass spectroscopy, including chlorinated hydrocarbons, have been found as a key pathway of chlorine removal from the catalyst. The exchange of chlorine for oxygen in the catalyst led to a significant decrease in the activity and production of higher hydrocarbons and their oxygenates as side products of the ODH reaction. Full article
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Open AccessArticle
Nonthermal Plasma Induced Fabrication of Solid Acid Catalysts for Glycerol Dehydration to Acrolein
Catalysts 2021, 11(3), 391; https://doi.org/10.3390/catal11030391 - 19 Mar 2021
Viewed by 384
Abstract
The feasibility of fabricating better solid acid catalysts using nonthermal plasma (NTP) technology for biobased acrolein production is demonstrated. NTP discharge exposure was integrated in catalyst fabrication in air or argon atmosphere. The fabricated catalysts were characterized by Brunauer–Emmett–Teller surface area analysis, temperature-programmed [...] Read more.
The feasibility of fabricating better solid acid catalysts using nonthermal plasma (NTP) technology for biobased acrolein production is demonstrated. NTP discharge exposure was integrated in catalyst fabrication in air or argon atmosphere. The fabricated catalysts were characterized by Brunauer–Emmett–Teller surface area analysis, temperature-programmed desorption of ammonia, X-ray powder diffraction and Fourier-transform infrared spectroscopy of pyridine adsorption, in comparison to regularly prepared catalysts as a control. Further, kinetic results collected via glycerol dehydration experiments were compared, and improvement in acrolein selectivity was displayed when the catalyst was fabricated in the argon NTP, but not in the air NTP. Possible mechanisms for the improvement were also discussed. Full article
(This article belongs to the Special Issue Towards Catalysts Prepared by Cold Plasma)
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Open AccessFeature PaperArticle
Highly Graphitized Fe-N-C Electrocatalysts Prepared from Chitosan Hydrogel Frameworks
Catalysts 2021, 11(3), 390; https://doi.org/10.3390/catal11030390 - 19 Mar 2021
Viewed by 592
Abstract
The development of platinum group metal-free (PGM-free) electrocatalysts derived from cheap and environmentally friendly biomasses for oxygen reduction reaction (ORR) is a topic of relevant interest, particularly from the point of view of sustainability. Fe-nitrogen-doped carbon materials (Fe-N-C) have attracted particular interest as [...] Read more.
The development of platinum group metal-free (PGM-free) electrocatalysts derived from cheap and environmentally friendly biomasses for oxygen reduction reaction (ORR) is a topic of relevant interest, particularly from the point of view of sustainability. Fe-nitrogen-doped carbon materials (Fe-N-C) have attracted particular interest as alternative to Pt-based materials, due to the high activity and selectivity of Fe-Nx active sites, the high availability and good tolerance to poisoning. Recently, many studies focused on developing synthetic strategies, which could transform N-containing biomasses into N-doped carbons. In this paper, chitosan was employed as a suitable N-containing biomass for preparing Fe-N-C catalyst in virtue of its high N content (7.1%) and unique chemical structure. Moreover, the major application of chitosan is based on its ability to strongly coordinate metal ions, a precondition for the formation of Fe-Nx active sites. The synthesis of Fe-N-C consists in a double step thermochemical conversion of a dried chitosan hydrogel. In acidic aqueous solution, the preparation of physical cross-linked hydrogel allows to obtain sophisticated organization, which assure an optimal mesoporosity before and after the pyrolysis. After the second thermal treatment at 900 °C, a highly graphitized material was obtained, which has been fully characterized in terms of textural, morphological and chemical properties. RRDE technique was used for understanding the activity and the selectivity of the material versus the ORR in 0.5 M H2SO4 electrolyte. Special attention was put in the determination of the active site density according to nitrite electrochemical reduction measurements. It was clearly established that the catalytic activity expressed as half wave potential linearly scales with the number of Fe-Nx sites. It was also established that the addition of the iron precursor after the first pyrolysis step leads to an increased activity due to both an increased number of active sites and of a hierarchical structure, which improves the access to active sites. At the same time, the increased graphitization degree, and a reduced density of pyrrolic nitrogen groups are helpful to increase the selectivity toward the 4e- ORR pathway. Full article
(This article belongs to the Special Issue Catalytic Properties of Nanostructured Electrodic Materials)
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Open AccessArticle
Enhanced Activity of Titanocene Complex for Electrocatalytic Nitrogen Reduction Reaction
Catalysts 2021, 11(3), 389; https://doi.org/10.3390/catal11030389 - 18 Mar 2021
Viewed by 399
Abstract
Enhanced titanocene (Cp2TiCl2) based electrocatalytic system for nitrogen reduction was shown, comprising glassy carbon electrode, high level of the catechol redox mediator, optimized binary THF/MeOH solvent and unique design of the reactor having ammonia permeable membrane at the outlet, [...] Read more.
Enhanced titanocene (Cp2TiCl2) based electrocatalytic system for nitrogen reduction was shown, comprising glassy carbon electrode, high level of the catechol redox mediator, optimized binary THF/MeOH solvent and unique design of the reactor having ammonia permeable membrane at the outlet, which allowed constant nitrogen flow through the working solution during entire electrolysis without risk of evaporation of the solvent. Catalytic activity was observed in the potential range of (−1.5)–(−2.3) V, reaching TON of 2.83%, corresponding to the production of 0.566 μmol NH3 (9.64 μg) in 24 h hydrolysis at −2.3 V using 0.02 mmol TiCp2Cl2 (5 mg). Full article
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Open AccessFeature PaperArticle
Nanosheet-Like Ho2O3 and Sr-Ho2O3 Catalysts for Oxidative Coupling of Methane
Catalysts 2021, 11(3), 388; https://doi.org/10.3390/catal11030388 - 18 Mar 2021
Viewed by 369
Abstract
In this work, Ho2O3 nanosheets were synthesized by a hydrothermal method. A series of Sr-modified Ho2O3 nanosheets (Sr-Ho2O3-NS) with a Sr/Ho molar ratio between 0.02 and 0.06 were prepared via an impregnation method. [...] Read more.
In this work, Ho2O3 nanosheets were synthesized by a hydrothermal method. A series of Sr-modified Ho2O3 nanosheets (Sr-Ho2O3-NS) with a Sr/Ho molar ratio between 0.02 and 0.06 were prepared via an impregnation method. These catalysts were characterized by several techniques such as XRD, N2 adsorption, SEM, TEM, XPS, O2-TPD (temperature-programmed desorption), and CO2-TPD, and they were studied with respect to their performances in the oxidative coupling of methane (OCM). In contrast to Ho2O3 nanoparticles, Ho2O3 nanosheets display greater CH4 conversion and C2-C3 selectivity, which could be related to the preferentially exposed (222) facet on the surface of the latter catalyst. The incorporation of small amounts of Sr into Ho2O3 nanosheets leads to a higher ratio of (O + O2)/O2− as well as an enhanced amount of chemisorbed oxygen species and moderate basic sites, which in turn improves the OCM performance. The optimal catalytic behavior is achievable on the 0.04Sr-Ho2O3-NS catalyst with a Sr/Ho molar ratio of 0.04, which gives a 24.0% conversion of CH4 with 56.7% selectivity to C2-C3 at 650 °C. The C2-C3 yield is well correlated with the amount of moderate basic sites present on the catalysts. Full article
(This article belongs to the Special Issue State-of-the-Art of Catalytical Technology in China)
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Open AccessFeature PaperReview
The Limonene Biorefinery: From Extractive Technologies to Its Catalytic Upgrading into p-Cymene
Catalysts 2021, 11(3), 387; https://doi.org/10.3390/catal11030387 - 18 Mar 2021
Viewed by 394
Abstract
Limonene is a renewable cyclic monoterpene that is easily obtainable from citrus peel and it is commonly used as a nutraceutical ingredient, antibacterial, biopesticide and green extraction solvent as well as additive in healthcare, fragrance and food and beverage industries for its characteristic [...] Read more.
Limonene is a renewable cyclic monoterpene that is easily obtainable from citrus peel and it is commonly used as a nutraceutical ingredient, antibacterial, biopesticide and green extraction solvent as well as additive in healthcare, fragrance and food and beverage industries for its characteristic lemon-like smell. Indeed, the lack of toxicity makes limonene a promising bio-alternative for the development of a wide range of effective products in modern biorefineries. As a consequence, industrial demand largely exceeds supply by now. Limonene can be also used as starting substrate for the preparation of building block chemicals, including p-cymene that is an important intermediate in several industrial catalytic processes. In this contribution, after reviewing recent advances in the recovery of limonene from citrus peel and residues with particular attention to benign-by-design extractive processes, we focus on the latest results in its dehydrogenation to p-cymene via heterogeneous catalysis. Indeed, the latest reports evidence that the selective production of p-cymene still remains a scientific and technological challenge since, in order to drive the isomerization and dehydrogenation of limonene, an optimal balance between the catalyst nature/content and the reaction conditions is needed. Full article
(This article belongs to the Section Biomass Catalysis)
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Open AccessArticle
Colour Changes during the Carbamazepine Oxidation by Photo-Fenton
Catalysts 2021, 11(3), 386; https://doi.org/10.3390/catal11030386 - 18 Mar 2021
Viewed by 333
Abstract
The oxidation of aqueous solutions of carbamazepine is conducted using the Fenton reagent, combined with the photolytic action of a 150 W medium pressure UV lamp, operating at T = 40 °C. The effect of acidity is analysed at an interval pH = [...] Read more.
The oxidation of aqueous solutions of carbamazepine is conducted using the Fenton reagent, combined with the photolytic action of a 150 W medium pressure UV lamp, operating at T = 40 °C. The effect of acidity is analysed at an interval pH = 2.0–5.0, verifying that operating at pH = 5.0 promotes colour formation (Colour = 0.15 AU). The effect of iron is studied, finding that the colour of the water increases in a linear way, Colour = 0.05 + 0.0075 [Fe]0. The oxidising action of hydrogen peroxide is tested, confirming that when operating with [H2O2]0 = 2.0 mM, the maximum colour is generated (Colourmax = 0.381 AU). The tint would be generated by the degradation of by-products of carbamazepine, which have chromophoric groups in their internal structure, such as oxo and dioxocarbazepines, which would produce tint along the first minutes of oxidation, while the formation of acridones would slowly induce colour in the water. Full article
(This article belongs to the Special Issue Photocatalysis in the Wastewater Treatment)
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Open AccessFeature PaperArticle
Evaluation of Efficient and Noble-Metal-Free NiTiO3 Nanofibers Sensitized with Porous gC3N4 Sheets for Photocatalytic Applications
Catalysts 2021, 11(3), 385; https://doi.org/10.3390/catal11030385 - 17 Mar 2021
Viewed by 363
Abstract
One-dimensional nickel titanate nanofibers (NiTiO3 NFs) were synthesized and loaded with acetic acid-treated exfoliated and sintered sheets of graphitic carbon nitride (AAs-gC3N4) to fabricate a unique heterogeneous structure. This novel fabrication method for porous AAs-gC3N4 [...] Read more.
One-dimensional nickel titanate nanofibers (NiTiO3 NFs) were synthesized and loaded with acetic acid-treated exfoliated and sintered sheets of graphitic carbon nitride (AAs-gC3N4) to fabricate a unique heterogeneous structure. This novel fabrication method for porous AAs-gC3N4 sheets using acetic acid-treated exfoliation followed by sintering provided gC3N4 with a surface area manifold larger than that of bulk gC3N4, with an abundance of catalytically active sites. Hybrid photocatalysts were synthesized through a two-step process. Firstly, NiTiO3 NFs (360 nm in diameter) were made by electrospinning, and these NiTiO3 NFs were sensitized with exfoliated gC3N4 sheets via a sonication process. Varying the weight ratio of NiTiO3 fibers to porous AAs-gC3N4 established that NiTiO3 NFs containing 40 wt% of porous AAs-gC3N4 exhibited optimal activity, i.e., removal of methylene blue and H2 evolution. After 60 min exposure to visible light irradiation, 97% of the methylene blue molecules were removed by the hybrid photocatalyst, compared with 82%, 72%, and 76% by pristine AAs-gC3N4, NiTiO3 NFs, and bulk gC3N4, respectively. The optimal structure also displayed excellent H2 evolution performance. The H2 evolution rate in the optimal sample (152 μmol g−1) was 2.2, 3.2 and 3-fold higher than that in pure AAs-gC3N4 (69 μmol g−1), NiTiO3 NFs (47 μmol g−1) and bulk gC3N4 (50 μmol g−1), respectively. This clearly shows that the holey AAs-gC3N4 nanosheets interacted synergistically with the NiTiO3 NFs. This extended the lifetime of photogenerated charge carriers and resulted in superior photocatalytic activity compared with pristine NiTiO3 NFs and bulk gC3N4. The higher Brunauer-Emmett-Teller surface area and the presence of many catalytically active sites also enhanced the photocatalytic performance of the hybrid sample. Moreover, through photoluminescence and photocurrent response analysis, a significant decrease in the recombination losses of the hybrid photocatalysts was also confirmed. Thus, this is a novel strategy to fabricate highly efficient photocatalysts with precisely tunable operating windows and enhanced charge separation. Full article
(This article belongs to the Special Issue Catalytic Materials for Application in Water Purification)
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Open AccessArticle
Natural Rocks–Heterogeneous Catalysts for Oil Transesterification in Biodiesel Synthesis
Catalysts 2021, 11(3), 384; https://doi.org/10.3390/catal11030384 - 16 Mar 2021
Viewed by 357
Abstract
Some of the more recent methods to produce biodiesel are based on heterogeneous catalysis, which has the advantage of easy separation of catalyst from the final product. In this paper, the heterogeneous transesterification of rapeseed oil with methanol is studied. The aim of [...] Read more.
Some of the more recent methods to produce biodiesel are based on heterogeneous catalysis, which has the advantage of easy separation of catalyst from the final product. In this paper, the heterogeneous transesterification of rapeseed oil with methanol is studied. The aim of this work was to investigate the possibilities of using natural catalysts in biodiesel synthesis and to determine the optimal conditions for this process. After the evaluation of catalytic effectiveness of rocks containing calcium and magnesium carbonates, it was determined that dolomite is the most effective catalyst in heterogeneous biodiesel synthesis. The optimal conditions of dolomite preparation are the following: heating at 850 °C for 5 h. The rapeseed oil transesterification was optimized by the application response surface methodology. Optimal conditions for the production of rapeseed methyl esters using dolomite as catalyst are the following: molar ratio of methanol to rapeseed oil of 11.94:1, reaction temperature of 64 °C, dolomite content of 6 wt%, reaction time of 5 h. Full article
(This article belongs to the Special Issue Green Chemistry and Sustainability in Catalysis)
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Open AccessFeature PaperArticle
Visible-Light Photocatalyst to Remove Indoor Ozone under Ambient Condition
Catalysts 2021, 11(3), 383; https://doi.org/10.3390/catal11030383 - 16 Mar 2021
Viewed by 328
Abstract
Ozone is a kind of hazardous gas in indoor areas and needs to be removed in order to protect the human respiratory system. Previous methods include physical adsorption, thermal treatment, electromagnetic radiation removal, catalysis and photocatalysis. However, they all have limited effects. This [...] Read more.
Ozone is a kind of hazardous gas in indoor areas and needs to be removed in order to protect the human respiratory system. Previous methods include physical adsorption, thermal treatment, electromagnetic radiation removal, catalysis and photocatalysis. However, they all have limited effects. This research introduced a novel milestone to remove indoor ozone by utilizing visible light photocatalysis technique under ambient condition. The modified sol–gel method was applied to prepare photocatalysts, strontium titanate (SrTiO3) and rhodium-doped strontium titanate (SrTiO3:Rh). In addition, the SrTiO3:Rh was further immersed in N3 dye to improve its photocatalytic performance. Batch system and continuous-flow system were used to quantify the removal rate of ozone and to measure the conversions of ozone, respectively. The results showed that SrTiO3:Rh possessed a higher ozone removal rate under a visible light condition compared with a commercial P25 TiO2 catalyst. In addition, SrTiO3:Rh based catalysts can also successfully perform visible light ozone photodecomposition in the continuous ozone flow system. Note that current ozone converters in aircraft utilize thermal-catalysts, which can only be operated at high temperature. This research reveals a promising catalysts and photo process, which can possibly replace the current aircraft ozone converters with visible-light driven converters, and boast higher performance under ambient condition. Full article
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Open AccessEditorial
Microporous Zeolites and Related Nanoporous Materials: Synthesis, Characterization and Application in Catalysis
Catalysts 2021, 11(3), 382; https://doi.org/10.3390/catal11030382 - 16 Mar 2021
Viewed by 350
Abstract
Microporous zeolites and related nanoporous materials have been studied intensively in academic and industrial laboratories around the world [...] Full article
Open AccessArticle
Tuning Structural Properties of WO3 Thin Films for Photoelectrocatalytic Water Oxidation
Catalysts 2021, 11(3), 381; https://doi.org/10.3390/catal11030381 - 16 Mar 2021
Viewed by 314
Abstract
The preparation of tungsten oxide (WO3) thin film by direct current (DC) reactive sputtering magnetron method and its photoelectrocatalytic properties for water oxidation reaction are investigated using ultraviolet-visible radiation. The structural, morphological, and compositional properties of WO3 are fine-tuned by [...] Read more.
The preparation of tungsten oxide (WO3) thin film by direct current (DC) reactive sputtering magnetron method and its photoelectrocatalytic properties for water oxidation reaction are investigated using ultraviolet-visible radiation. The structural, morphological, and compositional properties of WO3 are fine-tuned by controlling thin film deposition time, and post-annealing temperature and environment. The findings suggest that the band gap of WO3 can be controlled by adjusting the post-annealing temperature; the band gap decreased from 3.2 to 2.7 eV by increasing the annealing temperature from 100 to 600 °C. The theoretical calculations of the WO3 bandgap and the density of state are performed by density functional theory (DFT). Following the band gap modification, the photoelectrocatalytic activity increased and the maximum photocurrent (0.9 mA/cm2 at 0.6 VSCE) is recorded with WO3 film heated at 500 °C. The WO3 film heated under air exhibits much better performance in photoelectrochemical water oxidation process than that of annealed under inert atmosphere, due to its structural variation. The change in sputtering time leads to the formation of WO3 with varying film thickness, and the maximum photocurrent is observed when the film thickness is approximately 150 nm. The electrical conductivity and charge transfer resistance are measured and correlated to the properties and the performance of the WO3 photoelectrodes. In addition, the WO3 photoelectrode exhibits excellent photoelectrochemical stability. Full article
(This article belongs to the Special Issue Photoelectrochemical and Photocatalytic Materials for Fuel Production)
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Open AccessFeature PaperArticle
Selective and Efficient Olefin Epoxidation by Robust Magnetic Mo Nanocatalysts
Catalysts 2021, 11(3), 380; https://doi.org/10.3390/catal11030380 - 15 Mar 2021
Viewed by 287
Abstract
Iron oxide magnetic nanoparticles were synthesized with different sizes (11 and 30 nm). Subsequently they were shelled with a silica layer allowing grafting of an organic phosphine ligand that coordinated to the [MoI2(CO)3] organometallic core. The silica layer was [...] Read more.
Iron oxide magnetic nanoparticles were synthesized with different sizes (11 and 30 nm). Subsequently they were shelled with a silica layer allowing grafting of an organic phosphine ligand that coordinated to the [MoI2(CO)3] organometallic core. The silica layer was prepared by the Stöber method using either mechanical (both 11 and 30 nm nanoparticles) or ultrasound (30 nm only) stirring. The latter nanoparticles once coated with silica were obtained with less aggregation, which was beneficial for the final material holding the organometallic moiety. The Mo loadings were found to be 0.20, 0.18, and 0.34 mmolMo·g−1 for MNP30-Si-phos-Mo,MNP11-Si-phos-Mo, and MNP30-Sius-phos-Mo, respectively, with the ligand-to-metal ratio reaching 4.6, 4.8, and 3.2, by the same order, confirming coordination of the Mo moieties to two phos ligands. Structural characterization obtained from powder X-ray diffraction (XRD), scanning electron microscopy (SEM)/ transmission electron microscopy (TEM) analysis, and Fourier-transform infrared (FTIR) spectroscopy data confirmed the successful synthesis of all nanomaterials. Olefin epoxidation of several substrates catalyzed by these organometallic nano-hybrid materials using tert-butyl hydroperoxide (tbhp) as oxidant, achieved very good results. Extensive testing of the catalysts showed that they are highly active, selective, recyclable, and efficient concerning oxidant consumption. Full article
(This article belongs to the Special Issue Molybdenum Catalysis)
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Open AccessFeature PaperArticle
Solvothermal Crystallization of Ag/AgxO-AgCl Composites: Effect of Different Chloride Sources/Shape-Tailoring Agents
Catalysts 2021, 11(3), 379; https://doi.org/10.3390/catal11030379 - 15 Mar 2021
Viewed by 325
Abstract
In the present work, AgCl microcrystals were obtained by solvothermal crystallization to investigate the effect of H+, Na+, K+, and different shape-tailoring agents (non-ionic: polyvinylpyrrolidone vs. anionic: sodium dodecyl sulfate) on the textural and photocatalytic properties of [...] Read more.
In the present work, AgCl microcrystals were obtained by solvothermal crystallization to investigate the effect of H+, Na+, K+, and different shape-tailoring agents (non-ionic: polyvinylpyrrolidone vs. anionic: sodium dodecyl sulfate) on the textural and photocatalytic properties of the samples. The crystallization process resulted in secondary products, such as AgxO or Ag, AgClO3, AgClO4, which were further transformed during the photocatalytic tests. The most efficient photocatalyst (assessed for methyl orange degradation) was synthesized using HCl, as a chloride source and polyvinylpyrrolidone, as a shape-tailoring agent. Therefore, the ability of polyvinylpyrrolidone to enhance the photocatalytic activity was also investigated, and it was found that the addition of 0.6 g polyvinylpyrrolidone resulted in the most efficient photocatalyst. Moreover, AgxO, being a charge separator, could play a critical role in the photocatalytic process, while reversibly transforming to Ag back and forth. Full article
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Open AccessReview
The Influence of Copper on Halogenation/Dehalogenation Reactions of Aromatic Compounds and Its Role in the Destruction of Polyhalogenated Aromatic Contaminants
Catalysts 2021, 11(3), 378; https://doi.org/10.3390/catal11030378 - 14 Mar 2021
Viewed by 415
Abstract
The effect of copper and its compounds on halogenation and dehalogenation of aromatic compounds will be discussed in the proposed article. Cu oxidized to appropriate halides is an effective halogenation catalyst not only for the synthesis of halogenated benzenes or their derivatives as [...] Read more.
The effect of copper and its compounds on halogenation and dehalogenation of aromatic compounds will be discussed in the proposed article. Cu oxidized to appropriate halides is an effective halogenation catalyst not only for the synthesis of halogenated benzenes or their derivatives as desired organic fine chemicals, but is also an effective catalyst for the undesirable formation of thermodynamically stable and very toxic polychlorinated and polybrominated aromatic compounds such as polychlorinated biphenyls, dibenzo-p-dioxins and dibenzofurans accompanied incineration of waste contaminated with halogenated compounds or even inorganic halides. With appropriate change in reaction conditions, copper and its alloys or oxides are also able to effectively catalyze dehalogenation reactions, as will be presented in this review. Full article
(This article belongs to the Special Issue Gold, Silver and Copper Catalysis)
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