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2019 Volume 40 Issue 10
2019, 40(10):
Abstract:
2019, 40(10): 1405-1407
doi: S1872-2067(19)63443-1
Abstract:
2019, 40(10): 1408-1420
doi: S1872-2067(19)63399-1
Abstract:
Photoelectrochemical (PEC) water splitting capable of reducing and oxidizing water into hydrogen and oxygen in a generation mode of spatial separation has gained extensive popularity. In order to effectively produce hydrogen at the photocathode of a PEC cell, the photoanode, where the oxygen evolution reaction occurs, should be systematically developed on priority. In particular, WO3 has been identified as one of the most promising photoanode materials owing to its narrow band gap and high valence band position. Its practical implementation, however, is still limited by excessive electron-hole recombination and poor water oxidation kinetics. This review presents the various strategies that have been studied for enhancing the PEC water oxidation performance of WO3, such as controlling the morphology, introducing defects, constructing a heterojunction, loading a cocatalyst, and exploiting the plasmonic effect. In addition, the possible future research directions are presented.
Photoelectrochemical (PEC) water splitting capable of reducing and oxidizing water into hydrogen and oxygen in a generation mode of spatial separation has gained extensive popularity. In order to effectively produce hydrogen at the photocathode of a PEC cell, the photoanode, where the oxygen evolution reaction occurs, should be systematically developed on priority. In particular, WO3 has been identified as one of the most promising photoanode materials owing to its narrow band gap and high valence band position. Its practical implementation, however, is still limited by excessive electron-hole recombination and poor water oxidation kinetics. This review presents the various strategies that have been studied for enhancing the PEC water oxidation performance of WO3, such as controlling the morphology, introducing defects, constructing a heterojunction, loading a cocatalyst, and exploiting the plasmonic effect. In addition, the possible future research directions are presented.
2019, 40(10): 1421-1437
doi: S1872-2067(19)63408-X
Abstract:
CO2 is not only the most important greenhouse gas but also an important resource of elemental carbon and oxygen. From the perspective of resource and energy strategy, the conversion of CO2 to chemicals driven by renewable energy is of significance, since it can not only reduce carbon emission by the utilization of CO2 as feedstock but also store low-grade renewable energy as high energy density chemical energy. Although studies on photoelectrocatalytic reduction of CO2 using renewable energy are increasing, artificial bioconversion of CO2 as an important novel pathway to synthesize chemicals has attracted more and more attention. By simulating the natural photosynthesis process of plants and microorganisms, the artificial bioconversion of CO2 can efficiently synthesize chemicals via a designed and constructed artificial photosynthesis system. This review focuses on the recent advancements in artificial bioreduction of CO2, including the key techniques, and artificial biosynthesis of compounds with different carbon numbers. On the basis of the aforementioned discussions, we present the prospects for further development of artificial bioconversion of CO2 to chemicals.
CO2 is not only the most important greenhouse gas but also an important resource of elemental carbon and oxygen. From the perspective of resource and energy strategy, the conversion of CO2 to chemicals driven by renewable energy is of significance, since it can not only reduce carbon emission by the utilization of CO2 as feedstock but also store low-grade renewable energy as high energy density chemical energy. Although studies on photoelectrocatalytic reduction of CO2 using renewable energy are increasing, artificial bioconversion of CO2 as an important novel pathway to synthesize chemicals has attracted more and more attention. By simulating the natural photosynthesis process of plants and microorganisms, the artificial bioconversion of CO2 can efficiently synthesize chemicals via a designed and constructed artificial photosynthesis system. This review focuses on the recent advancements in artificial bioreduction of CO2, including the key techniques, and artificial biosynthesis of compounds with different carbon numbers. On the basis of the aforementioned discussions, we present the prospects for further development of artificial bioconversion of CO2 to chemicals.
2019, 40(10): 1438-1487
doi: S1872-2067(19)63400-5
Abstract:
Nanosize cerium-zirconium solid solution (CZO) with a special fluorite structure has received an increasing research interest due to their remarkable advantages such as excellent oxygen storage capacity and great flexibility in their composition and structure. By partial metal (including rare earth, transition, alkaline earth or other metal) doping into CZO, the physicochemical properties of these catalytic materials can be controllable adjusted for the study of specific reactions. To date, nanosize CZO has been prepared by co-precipitation, sol-gel, surfactant-assisted approach, solution combustion, micro-emulsion, high energy mechanical milling, etc. The advent of these methodologies has prompted researchers to construct well-defined networks with customized micromorphology and functionalities. In this review, we describe not only the basic structure and synthetic strategies of CZO, but also their relevant applications in environmental catalysis, such as the purification for CO, nitrogen oxides (NOx), volatile organic compounds (VOC), soot, hydrocarbon (HC), CO2 and solid particulate matters (PM), and some reaction mechanisms are also summarized.
Nanosize cerium-zirconium solid solution (CZO) with a special fluorite structure has received an increasing research interest due to their remarkable advantages such as excellent oxygen storage capacity and great flexibility in their composition and structure. By partial metal (including rare earth, transition, alkaline earth or other metal) doping into CZO, the physicochemical properties of these catalytic materials can be controllable adjusted for the study of specific reactions. To date, nanosize CZO has been prepared by co-precipitation, sol-gel, surfactant-assisted approach, solution combustion, micro-emulsion, high energy mechanical milling, etc. The advent of these methodologies has prompted researchers to construct well-defined networks with customized micromorphology and functionalities. In this review, we describe not only the basic structure and synthetic strategies of CZO, but also their relevant applications in environmental catalysis, such as the purification for CO, nitrogen oxides (NOx), volatile organic compounds (VOC), soot, hydrocarbon (HC), CO2 and solid particulate matters (PM), and some reaction mechanisms are also summarized.
2019, 40(10): 1488-1493
doi: S1872-2067(19)63413-3
Abstract:
The surface modification of metal oxides using organic modifiers is a potential strategy for enhancing their catalytic performances. In this study, a hydrophobic surface amine-modified CoO catalyst with a water contact angle of 143° was fabricated. The catalyst was characterized by XRD, TGA, FT-IR, HR-TEM, and XPS. The results showed that the fabricated catalyst performed better than the hydrophilic commercial CoO nanoparticle in the process of aromatic hydrocarbon oxidation. After the amines modification, commercial CoO also became hydrophobic and improved conversion of ethylbenzene was achieved. The surface modification of CoO with amines induced the hydrophobicity property, which could serve as a reference for the design of other hydrophobic catalysts.
The surface modification of metal oxides using organic modifiers is a potential strategy for enhancing their catalytic performances. In this study, a hydrophobic surface amine-modified CoO catalyst with a water contact angle of 143° was fabricated. The catalyst was characterized by XRD, TGA, FT-IR, HR-TEM, and XPS. The results showed that the fabricated catalyst performed better than the hydrophilic commercial CoO nanoparticle in the process of aromatic hydrocarbon oxidation. After the amines modification, commercial CoO also became hydrophobic and improved conversion of ethylbenzene was achieved. The surface modification of CoO with amines induced the hydrophobicity property, which could serve as a reference for the design of other hydrophobic catalysts.
2019, 40(10): 1494-1498
doi: S1872-2067(19)63420-0
Abstract:
A simple and efficient method for the synthesis of 2-sulfonylquinoline from deoxygenative C2-sulfonylation of quinoline N-oxides with sulfinic acid induced by visible light is presented. This protocol shows a broad substrate scope, and desired products with various substituents can be formed in moderate to high yields at room temperature.
A simple and efficient method for the synthesis of 2-sulfonylquinoline from deoxygenative C2-sulfonylation of quinoline N-oxides with sulfinic acid induced by visible light is presented. This protocol shows a broad substrate scope, and desired products with various substituents can be formed in moderate to high yields at room temperature.
2019, 40(10): 1499-1504
doi: S1872-2067(19)63423-6
Abstract:
Nanoclusters with a precise number of atoms may exhibit unique and often unexpected catalytic properties. Here, we report an atomically precise Pd3 nanocluster as an efficient catalyst, whose catalytic performance differs remarkably from typical Pd nanoparticle catalysts, with excellent reactivity and selectivity in the one-pot synthesis of benzalaniline from nitrobenzene and benzaldehyde. We anticipate that our work will serve as a starting point for the catalytic applications of these tiny atomically precise nanoclusters in green chemistry for the one-pot syntheses of fine chemicals.
Nanoclusters with a precise number of atoms may exhibit unique and often unexpected catalytic properties. Here, we report an atomically precise Pd3 nanocluster as an efficient catalyst, whose catalytic performance differs remarkably from typical Pd nanoparticle catalysts, with excellent reactivity and selectivity in the one-pot synthesis of benzalaniline from nitrobenzene and benzaldehyde. We anticipate that our work will serve as a starting point for the catalytic applications of these tiny atomically precise nanoclusters in green chemistry for the one-pot syntheses of fine chemicals.
2019, 40(10): 1505-1515
doi: S1872-2067(19)63418-2
Abstract:
Despite of extensive attention on the copper-based heterogeneous oxidative homocoupling of alkynes (OHA) to 1,3-diynes, the photocatalytic OHA is scarcely investigated. By screening copper-containing spinel catalysts, we discovered that a prereduced copper ferrite (CuFe2O4) not only can catalyze the thermocatalytic OHA but also is efficient for the photocatalytic OHA under visible light irradiation. It is found that the sol-gel combustion (SG) method and the partial reduction at 250℃ can result in the optimal CuFe2O4-SG-250 catalyst showing high activity and stability. Surface oxidized Cu2O is evidenced to be the active species for the thermocatalytic OHA, whereas metallic copper nanopaticles (CuNPs) are identified as the active sites for the photocatalytic OHA. The efficiency of photocatalytic OHA at ambient temperature is comparable to that of thermocatalytic OHA at 120℃, and the CuFe2O4-SG-250 catalyst can be magnetically separated and reused at least five times. The localized surface plasmon resonance effect of CuNPs contributes to visible light-induced photocatalytic OHA.
Despite of extensive attention on the copper-based heterogeneous oxidative homocoupling of alkynes (OHA) to 1,3-diynes, the photocatalytic OHA is scarcely investigated. By screening copper-containing spinel catalysts, we discovered that a prereduced copper ferrite (CuFe2O4) not only can catalyze the thermocatalytic OHA but also is efficient for the photocatalytic OHA under visible light irradiation. It is found that the sol-gel combustion (SG) method and the partial reduction at 250℃ can result in the optimal CuFe2O4-SG-250 catalyst showing high activity and stability. Surface oxidized Cu2O is evidenced to be the active species for the thermocatalytic OHA, whereas metallic copper nanopaticles (CuNPs) are identified as the active sites for the photocatalytic OHA. The efficiency of photocatalytic OHA at ambient temperature is comparable to that of thermocatalytic OHA at 120℃, and the CuFe2O4-SG-250 catalyst can be magnetically separated and reused at least five times. The localized surface plasmon resonance effect of CuNPs contributes to visible light-induced photocatalytic OHA.
2019, 40(10): 1516-1524
doi: S1872-2067(19)63386-3
Abstract:
The selective hydrogenation of phenol to cyclohexanone is an important process in the chemical industry. However, achieving high selectivity at high conversion rates is highly challenging, particularly under continuous reaction conditions. Here, we found that the presence of Na alkaline additives (NaX, X=CO32-, HCO3-, or OH-) on Pd/Al2O3 not only promoted the phenol conversion from 8.3% to >99% but also increased the cyclohexanone selectivity from 89% to >97% during the continuous hydrogenation of phenol on a fixed bed reactor. After 1200 h of continuous reaction, no activity or selectivity attenuation was observed and the turnover number was approximately 2.9×105. Density functional theory calculations, spectroscopic, and dynamics studies demonstrated that the addition of NaX greatly promoted phenol adsorption and hydrogen activation, thereby improving catalytic activity. Simultaneously, the formation of a "-C=O-Na-" intermediate inhibited the excessive hydrogenation and intermolecular coupling of cyclohexanone, leading to high selectivity.
The selective hydrogenation of phenol to cyclohexanone is an important process in the chemical industry. However, achieving high selectivity at high conversion rates is highly challenging, particularly under continuous reaction conditions. Here, we found that the presence of Na alkaline additives (NaX, X=CO32-, HCO3-, or OH-) on Pd/Al2O3 not only promoted the phenol conversion from 8.3% to >99% but also increased the cyclohexanone selectivity from 89% to >97% during the continuous hydrogenation of phenol on a fixed bed reactor. After 1200 h of continuous reaction, no activity or selectivity attenuation was observed and the turnover number was approximately 2.9×105. Density functional theory calculations, spectroscopic, and dynamics studies demonstrated that the addition of NaX greatly promoted phenol adsorption and hydrogen activation, thereby improving catalytic activity. Simultaneously, the formation of a "-C=O-Na-" intermediate inhibited the excessive hydrogenation and intermolecular coupling of cyclohexanone, leading to high selectivity.
2019, 40(10): 1525-1533
doi: S1872-2067(19)63415-7
Abstract:
Hexanal is a typical indoor odorant from wood-based products, which induces discomfort and irritation to human beings. The removal of hexanal has rarely been investigated. In this study, we found that the amount of Mn vacancies in γ-MnOOH significantly affects its catalytic activity toward hexanal degradation and transformation into CO2. The as-synthesized Mn vacancy-rich γ-MnOOH exhibited high efficiency toward hexanal removal, achieving 100% degradation of 15 ppm hexanal at 85℃ and complete transformation into CO2 at 160℃ under the gas hourly space velocity of 240 L/(g·h); its activity could be completely regenerated by in-situ heat treatment at 180℃. Moreover, it was found that the degradation of hexanal occurred in a stepwise manner, i.e., losing one CH2 unit per step. Electron spinning resonance studies detected strong indicative signals for the presence of the superoxide anion radical (·O2-) on Mn-vacancy-rich γ-MnOOH, which may act as active oxygen species for the hexanal degradation. Understanding the role of Mn-vacancy and the mechanism of hexanal degradation by γ-MnOOH are essential for developing efficient oxide catalysts for volatile organic compounds besides hexanal.
Hexanal is a typical indoor odorant from wood-based products, which induces discomfort and irritation to human beings. The removal of hexanal has rarely been investigated. In this study, we found that the amount of Mn vacancies in γ-MnOOH significantly affects its catalytic activity toward hexanal degradation and transformation into CO2. The as-synthesized Mn vacancy-rich γ-MnOOH exhibited high efficiency toward hexanal removal, achieving 100% degradation of 15 ppm hexanal at 85℃ and complete transformation into CO2 at 160℃ under the gas hourly space velocity of 240 L/(g·h); its activity could be completely regenerated by in-situ heat treatment at 180℃. Moreover, it was found that the degradation of hexanal occurred in a stepwise manner, i.e., losing one CH2 unit per step. Electron spinning resonance studies detected strong indicative signals for the presence of the superoxide anion radical (·O2-) on Mn-vacancy-rich γ-MnOOH, which may act as active oxygen species for the hexanal degradation. Understanding the role of Mn-vacancy and the mechanism of hexanal degradation by γ-MnOOH are essential for developing efficient oxide catalysts for volatile organic compounds besides hexanal.
2019, 40(10): 1534-1539
doi: S1872-2067(19)63388-7
Abstract:
The interfacial perimeter of gold nanocatalysts is popularly viewed as the active sites for a number of chemical reactions, while the geometrical structure of the interface at atomic scale is less known. Here, TiO2-nanosheets and nanospindles were adapted to accommodate Au particles (~2.2 nm), forming Au-TiO2{001} and Au-TiO2{101} interfaces. Upon calcination at 623 K in air, HAADF-STEM images evidenced that the Au particles on TiO2{101} enlarged to 3.1 nm and these on TiO2{001} remained unchanged, suggesting the stronger metal-support interaction on TiO2{001}. Au/TiO2{001} was more active for CO oxidation than Au/TiO2{101} system.
The interfacial perimeter of gold nanocatalysts is popularly viewed as the active sites for a number of chemical reactions, while the geometrical structure of the interface at atomic scale is less known. Here, TiO2-nanosheets and nanospindles were adapted to accommodate Au particles (~2.2 nm), forming Au-TiO2{001} and Au-TiO2{101} interfaces. Upon calcination at 623 K in air, HAADF-STEM images evidenced that the Au particles on TiO2{101} enlarged to 3.1 nm and these on TiO2{001} remained unchanged, suggesting the stronger metal-support interaction on TiO2{001}. Au/TiO2{001} was more active for CO oxidation than Au/TiO2{101} system.
2019, 40(10): 1540-1547
doi: S1872-2067(19)63401-7
Abstract:
The development of highly efficient and cost-effective electrode materials for catalyzing the oxygen evolution reaction (OER) is crucial for water splitting technology. The increase in the number of active sites by tuning the morphology and structure and the enhancement of the reactivity of active sites by the incorporation of other components are the two main strategies for the enhancement of their catalytic performance. In this study, by combining these two strategies, a unique three-dimensional nanoporous Fe-Co oxyhydroxide layer coated on the carbon cloth (3D-FeCoOOH/CC) was successfully synthesized by in situ electro-oxidation methods, and directly used as a working electrode. The electrode, 3D-FeCoOOH/CC, was obtained by the Fe doping process in (NH4)2Fe(SO4)2, followed by continuous in situ electro-oxidization in alkaline medium of "micro go chess piece" arrays on the carbon cloth (MCPAs/CC). Micro characterizations illustrated that the go pieces of MCPAs/CC were completely converted into a thin conformal coating on the carbon cloth fibers. The electrochemical test results showed that the as-synthesized 3D-FeCoOOH/CC exhibited enhanced activity for OER with a low overpotential of 259 mV, at a current density of 10 mA cm-2, and a small Tafel slope of 34.9 mV dec-1, as well as superior stability in 1.0 mol L-1 KOH solution. The extensive analysis revealed that the improved electrochemical surface area, conductivity, Fe-Co bimetallic composition, and the unique 3D porous structure together contributed to the enhanced OER activity of 3D-FeCoOOH/CC. Furthermore, the synthetic strategy applied in this study could be extended to fabricate a series of Co-based electrode materials with the dopant of other transition elements.
The development of highly efficient and cost-effective electrode materials for catalyzing the oxygen evolution reaction (OER) is crucial for water splitting technology. The increase in the number of active sites by tuning the morphology and structure and the enhancement of the reactivity of active sites by the incorporation of other components are the two main strategies for the enhancement of their catalytic performance. In this study, by combining these two strategies, a unique three-dimensional nanoporous Fe-Co oxyhydroxide layer coated on the carbon cloth (3D-FeCoOOH/CC) was successfully synthesized by in situ electro-oxidation methods, and directly used as a working electrode. The electrode, 3D-FeCoOOH/CC, was obtained by the Fe doping process in (NH4)2Fe(SO4)2, followed by continuous in situ electro-oxidization in alkaline medium of "micro go chess piece" arrays on the carbon cloth (MCPAs/CC). Micro characterizations illustrated that the go pieces of MCPAs/CC were completely converted into a thin conformal coating on the carbon cloth fibers. The electrochemical test results showed that the as-synthesized 3D-FeCoOOH/CC exhibited enhanced activity for OER with a low overpotential of 259 mV, at a current density of 10 mA cm-2, and a small Tafel slope of 34.9 mV dec-1, as well as superior stability in 1.0 mol L-1 KOH solution. The extensive analysis revealed that the improved electrochemical surface area, conductivity, Fe-Co bimetallic composition, and the unique 3D porous structure together contributed to the enhanced OER activity of 3D-FeCoOOH/CC. Furthermore, the synthetic strategy applied in this study could be extended to fabricate a series of Co-based electrode materials with the dopant of other transition elements.
2019, 40(10): 1548-1556
doi: S1872-2067(19)63398-X
Abstract:
The development of heterogeneous catalytic processes is crucial for the synthesis of chiral compounds for both academic and industrial applications. However, thus far, such achievements have remained elusive. Herein, we report the heterogeneous asymmetric hydrogenation of 2-methylquinoline over solid chiral catalysts, which were prepared by the one-pot polymerization of (1R,2R)-N-(4-vinyl-benzenesulfonyl)-1,2-diphenylethane-1,2-diamine (VDPEN) and divinylbenzene (DVB) in the presence or absence of activated carbon (C) or carbon nanotubes (CNTs), followed by Ru coordination and anion exchange. The solid chiral catalysts were fully characterized by N2 sorption analysis, elemental analysis, TEM, FT-IR spectroscopy, and 13C CP-MAS NMR. All the solid chiral catalysts could efficiently catalyze the asymmetric hydrogenation of 2-methylquinoline to afford 2-methyl-1,2,3,4-tetrahydroquinoline with 90% ee. Studies have shown that polymer/C and polymer/CNTs composites are more active than pure polymers. The polymer/CNTs composite exhibited the highest activity among all the solid chiral catalysts under identical conditions, owing to the unique morphology of CNTs. The recycling stabilities of the solid chiral catalysts were greatly improved when ionic liquids (ILs) were employed as solvents; this is mainly attributed to the decreased leaching amount of anions owing to the confinement effect of ILs on ionic compounds.
The development of heterogeneous catalytic processes is crucial for the synthesis of chiral compounds for both academic and industrial applications. However, thus far, such achievements have remained elusive. Herein, we report the heterogeneous asymmetric hydrogenation of 2-methylquinoline over solid chiral catalysts, which were prepared by the one-pot polymerization of (1R,2R)-N-(4-vinyl-benzenesulfonyl)-1,2-diphenylethane-1,2-diamine (VDPEN) and divinylbenzene (DVB) in the presence or absence of activated carbon (C) or carbon nanotubes (CNTs), followed by Ru coordination and anion exchange. The solid chiral catalysts were fully characterized by N2 sorption analysis, elemental analysis, TEM, FT-IR spectroscopy, and 13C CP-MAS NMR. All the solid chiral catalysts could efficiently catalyze the asymmetric hydrogenation of 2-methylquinoline to afford 2-methyl-1,2,3,4-tetrahydroquinoline with 90% ee. Studies have shown that polymer/C and polymer/CNTs composites are more active than pure polymers. The polymer/CNTs composite exhibited the highest activity among all the solid chiral catalysts under identical conditions, owing to the unique morphology of CNTs. The recycling stabilities of the solid chiral catalysts were greatly improved when ionic liquids (ILs) were employed as solvents; this is mainly attributed to the decreased leaching amount of anions owing to the confinement effect of ILs on ionic compounds.
2019, 40(10): 1557-1565
doi: S1872-2067(19)63416-9
Abstract:
Owing to Fe being the most abundant and least expensive transition metal on the earth, the utilization of Fe-based catalysts for catalytic hydrogenation has attracted worldwide attention. In this work, a series of N-doped C supported Fe catalysts (Fe-N-C) were prepared by co-pyrolysis of cellulose and ferric chloride under ammonia atmosphere. Characterization methods such as elemental analysis, atomic absorption spectroscopy, nitrogen adsorption-desorption isotherms, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were carried out to explore the physicochemical properties of the catalysts. Using hydrogenation of nitrobenzene as a model reaction, the catalysts prepared at different pyrolysis temperatures displayed different activities. Fe-N-C-700 exhibited the best activity among these catalysts, with the yield of aniline being up to 98.0% under 5 MPa H2 at 120℃ after 12 h. Combined with the results of catalyst characterization and comparative tests, the transformation of Fe species and the generation of N-doped C, especially graphitized N-doped C, in the catalyst may be the main factors affecting the activity. A kinetic study was carried out and the apparent activation energy was obtained as 31.53 kJ/mol. The stability of the catalyst was also tested and no significant decrease in the activity was observed after 5 runs.
Owing to Fe being the most abundant and least expensive transition metal on the earth, the utilization of Fe-based catalysts for catalytic hydrogenation has attracted worldwide attention. In this work, a series of N-doped C supported Fe catalysts (Fe-N-C) were prepared by co-pyrolysis of cellulose and ferric chloride under ammonia atmosphere. Characterization methods such as elemental analysis, atomic absorption spectroscopy, nitrogen adsorption-desorption isotherms, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were carried out to explore the physicochemical properties of the catalysts. Using hydrogenation of nitrobenzene as a model reaction, the catalysts prepared at different pyrolysis temperatures displayed different activities. Fe-N-C-700 exhibited the best activity among these catalysts, with the yield of aniline being up to 98.0% under 5 MPa H2 at 120℃ after 12 h. Combined with the results of catalyst characterization and comparative tests, the transformation of Fe species and the generation of N-doped C, especially graphitized N-doped C, in the catalyst may be the main factors affecting the activity. A kinetic study was carried out and the apparent activation energy was obtained as 31.53 kJ/mol. The stability of the catalyst was also tested and no significant decrease in the activity was observed after 5 runs.
2019, 40(10): 1566-1575
doi: S1872-2067(19)63396-6
Abstract:
An efficient chiral Brønsted acid-catalyzed conjugate addition of indoles to azadienes has been successfully developed, which enables a facile approach to optically active hetero-triarylmethanes with excellent enantioselectivities and broad substrate scope. This chiral Brønsted acid catalytic system provides a new opportunity for the development of asymmetric reactions of azadienes.
An efficient chiral Brønsted acid-catalyzed conjugate addition of indoles to azadienes has been successfully developed, which enables a facile approach to optically active hetero-triarylmethanes with excellent enantioselectivities and broad substrate scope. This chiral Brønsted acid catalytic system provides a new opportunity for the development of asymmetric reactions of azadienes.
2019, 40(10): 1576-1584
doi: S1872-2067(19)63414-5
Abstract:
Exploration of cost-effective electrocatalysts for boosting the overall water-splitting efficiency is vitally important for obtaining renewable fuels such as hydrogen. Here, earth-abundant CoxNi1-xO nanowire arrays were used as a structural framework to dilute Ir incorporation for fabricating electrocatalysts for water splitting. Minimal Ir-incorporated CoxNi1-xO nanowire arrays were synthesized through the facile hydrothermal method with subsequent calcination by using Ni foam (NF) as both the substrate and source of Ni. The electrocatalytic water-splitting performance was found to crucially depend on the Ir content of the parent CoxNi1-xO nanowire arrays. As a result, for a minimal Ir content, as low as 0.57 wt%, the obtained Ir-CoxNi1-xO/NF electrodes exhibited optimal catalytic activity in terms of a low overpotential of 260 mV for the oxygen evolution reaction and 53 mV for the hydrogen evolution reaction at 10 mA cm-2 in 1 mol L-1 KOH. When used as bifunctional electrodes in water splitting, the current density of 10 mA cm-2 was obtained at a low cell voltage of 1.55 V. Density functional theory calculations revealed that the Ir-doped CoxNi1-xO arrays exhibited enhanced electrical conductivity and low Gibbs free energy, which contributed to the improved electrocatalytic activity. The present study presents a new strategy for the development of transition metal oxide electrocatalysts with low levels of Ir incorporation for efficient water splitting.
Exploration of cost-effective electrocatalysts for boosting the overall water-splitting efficiency is vitally important for obtaining renewable fuels such as hydrogen. Here, earth-abundant CoxNi1-xO nanowire arrays were used as a structural framework to dilute Ir incorporation for fabricating electrocatalysts for water splitting. Minimal Ir-incorporated CoxNi1-xO nanowire arrays were synthesized through the facile hydrothermal method with subsequent calcination by using Ni foam (NF) as both the substrate and source of Ni. The electrocatalytic water-splitting performance was found to crucially depend on the Ir content of the parent CoxNi1-xO nanowire arrays. As a result, for a minimal Ir content, as low as 0.57 wt%, the obtained Ir-CoxNi1-xO/NF electrodes exhibited optimal catalytic activity in terms of a low overpotential of 260 mV for the oxygen evolution reaction and 53 mV for the hydrogen evolution reaction at 10 mA cm-2 in 1 mol L-1 KOH. When used as bifunctional electrodes in water splitting, the current density of 10 mA cm-2 was obtained at a low cell voltage of 1.55 V. Density functional theory calculations revealed that the Ir-doped CoxNi1-xO arrays exhibited enhanced electrical conductivity and low Gibbs free energy, which contributed to the improved electrocatalytic activity. The present study presents a new strategy for the development of transition metal oxide electrocatalysts with low levels of Ir incorporation for efficient water splitting.
