104 results
Search Results
2. Reactivity of a series of triaryl borates, B(OArx)3, in hydroboration catalysis.
- Author
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Sokolnicki, Tomasz, Alharbi, Mashael M., van Ingen, Yara, Rahim, Shahnaz, Pramanik, Milan, Roldan, Alberto, Walkowiak, Jędrzej, and Melen, Rebecca L.
- Subjects
HYDROBORATION ,BORATES ,CATALYSIS ,CATALYSTS ,ALKYNES - Abstract
In this paper, we compare the reactivity of a series of triaryl borates B(OAr
x )3 as catalysts for the hydroboration of alkenes and alkynes. It was observed that commercially available B(OPh)3 performed the poorest, whereas catalysts with o-F atoms appeared to perform much better. [ABSTRACT FROM AUTHOR]- Published
- 2023
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3. Stepwise synthesis and catalysis in C–S cross-coupling of pyridine-functionalized N-heterocyclic carbene nickel(II) complexes by mechanochemistry.
- Author
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Cui, Xiaoxiao, Hao, Xiujia, and Guo, Fang
- Subjects
MECHANICAL chemistry ,CATALYSIS ,NICKEL catalysts ,CATALYSTS ,SALTS - Abstract
The synthesis of three N-heterocyclic carbene complexes by stepwise grinding is described in this paper. The benzimidazolium salts ([H
2 L]Br2 and [H2 L](PF6 )2 ([H2 L] = 1,1′-di(2-picolyl)-3,3′-methylenedibenzoimidazolium)) were initially prepared. Their reactions with Ni(OAc)2 ·4H2 O by grinding afforded three nickel complexes, [NiL]Br2 ·CH3 OH (1), [NiL]Br2 ·2H2 O (1′) and [NiL](PF6 )2 ·0.5CH3 CN (2), respectively. A five-coordinated complex [NiLBr]PF6 (3) was further obtained by grinding NH4 PF6 with complex 1 or 1′, or grinding KBr with complex 2. Complex 3 can also be obtained by direct grinding of complexes 1/1′ and 2. Complex 3 was subsequently used as a catalyst in the C–S bond cross-coupling of 2-bromoacetophenone and 2-mercaptobenzothiazole. The entire procedure from the synthesis to the catalytic reaction was performed by mechanochemistry. The green metrics E-factor and EcoScale close to ideal values showed the eco-friendly nature of the entire procedure. [ABSTRACT FROM AUTHOR]- Published
- 2022
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4. Copper-catalysed electrophilic carboamination of terminal alkynes with benzyne looked at through the computational lens.
- Author
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Tobisch, Sven
- Subjects
AMINATION ,ALKYNES ,COPPER ,OXIDATIVE addition ,CATALYSIS ,CATALYSTS - Abstract
A detailed computational mechanistic study of the copper-catalysed three-component-type electrophilic carboamination of terminal alkynes with benzyne and an archetypal O-benzoylhydroxylamine electrophile is presented. Probing various plausible pathways for relevant elementary steps and scrutinising performance degradation pathways, with the aid of a reliable computational protocol applied to a realistic catalyst model combined with kinetic analysis, identified the pathways preferably traversed in productive catalysis. It entails rapid alkynylcupration of in situ generated benzyne to deliver the arylcopper nucleophile that undergoes amination with the O-benzoylhydroxylamine electrophile to afford copper benzoate. Umpolung-enabled electrophilic amination favours a multistep S
N 2-type oxidative addition/N–C bond-forming reductive elimination sequence involving a short-lived formal {P^P}CuIII carboxylate amido aryl intermediate. SN 2-type displacement of the benzoate leaving group at the arylcopper nucleophile, which represents the catalyst resting state, is predicted to be the turnover limiting step. Alkynolysis transforms copper benzoate back to catalytically competent alkynylcopper. The computational probe of a wider range of substrates reveals that only severely ring-strained C6 -arynes, C6 -cycloalkynes and electron-deficient cyclopropenes featuring a highly reactive C≡C linkage could replace benzyne. Moreover, strict control of stationary benzyne concentration is indispensable for electrophilic carboamination to ever become achievable. [ABSTRACT FROM AUTHOR]- Published
- 2024
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5. Rationally constructing hollow N-doped carbon supported Ru catalysts for enhanced hydrogenation catalysis.
- Author
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Liu, Tiantian, Li, Jing, Yan, Xiaorui, Li, Kairui, Wang, Wenhua, and Wei, Haisheng
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RUTHENIUM catalysts ,CATALYST supports ,DOPING agents (Chemistry) ,HYDROGENATION ,CATALYSIS ,CATALYSTS - Abstract
The availability of catalytic sites for contact with reactants is a key issue to improve the performance of a catalyst, where constructing hollow structured nanomaterials has been considered as an effective strategy. Here, an N-doped carbon supported Ru catalyst with an interior cavity was synthesized by etching a MOF-derived core–shell precursor, in which metal Ru can be highly dispersed in the porous shell. This catalyst shows 98.7% conversion and >99% selectivity towards p-chloroaniline in the hydrogenation of p-chloronitrobenzene, which is better than the corresponding supported catalyst. Moreover, it also displays excellent stability with 5 cycle runs and good substrate universality for the hydrogenation of extensive substituted nitroarenes. Various characterization techniques and control experiments reveal the advantage of the unique structure to promote the mass transport and adsorption of reactant molecules on Ru sites. This work provides a novel strategy to design an efficient Ru-based catalyst for chemoselective hydrogenation. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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6. Unprecedented Mo3S4 cluster-catalyzed radical C–C cross-coupling reactions of aryl alkynes and acrylates.
- Author
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Mateu-Campos, Juanjo, Guillamón, Eva, Safont, Vicent S., Junge, Kathrin, Junge, Henrik, Beller, Matthias, and Llusar, Rosa
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RADICALS (Chemistry) ,ACRYLATES ,ALKYNES ,CATALYSTS ,CATALYSIS ,HYDROGEN - Abstract
A new method for the generation of benzyl radicals from terminal aromatic alkynes has been developed, which allows the direct cross coupling with acrylate derivatives. Our additive-free protocol employs air-stable diamino Mo
3 S4 cubane-type cluster catalysts in the presence of hydrogen. A sulfur-centered cluster catalysis mechanism for benzyl radical formation is proposed based on catalytic and stoichiometric experiments. The process starts with the cluster hydrogen activation to form a bis(hydrosulfido) [Mo3 (μ3 -S)(μ-S)(μ-SH)2 Cl3 (dmen)3 ]+ intermediate. The reaction of various aromatic terminal alkynes containing different functionalities with a series of acrylates affords the corresponding Giese-type radical addition products. [ABSTRACT FROM AUTHOR]- Published
- 2024
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7. Solar CO2 reduction using a molecular Re(I) catalyst grafted on SiO2via amide and alkyl amine linkages.
- Author
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Fenton, Thomas, Ahmad, Esraa, and Li, Gonghu
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CHEMICAL amplification ,CATALYSTS ,CATALYSIS ,CATALYTIC activity ,PHOTOREDUCTION ,AMIDES ,COBALT catalysts - Abstract
Heterogenized molecular catalysts have shown interesting activities in different chemical transformations. In our previous studies, a molecular catalyst, Re(bpy)(CO)
3 Cl where bpy is 2,2′-bipyridine, was covalently attached to silica surfaces via an amide linkage for use in photocatalytic CO2 reduction. Derivatizing the bpy ligand with electron-withdrawing amide groups led to detrimental effects on the catalytic activity of Re(bpy)(CO)3 Cl. In this study, an alkyl amine linkage is utilized to attach Re(bpy)(CO)3 Cl onto SiO2 in order to eliminate the detrimental effects of the amide linkage by breaking the conjugation between the bpy ligand and the amide group. However, the heterogenized Re(I) catalyst containing the alkyl amine linkage demonstrates even lower activity than the one containing the amide linkage in photocatalytic CO2 reduction. Infrared studies suggest that the presence of the basic amine group led to the formation of a photocatalytically inactive Re(I)-OH species on SiO2 . Furthermore, the amine group likely contributes to the stabilization of a surface Re(I)-carboxylato species formed upon light irradiation, resulting in the low activity of the heterogenized Re(I) catalyst containing the alkyl amine linkage. [ABSTRACT FROM AUTHOR]- Published
- 2024
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8. Interfacial engineering to construct an IrOx/WO3 hetero-structured catalyst for efficient acidic OER catalysis.
- Author
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Guan, Zeyu, Weng, Yuxiao, Li, Jiankun, Li, Shiyi, Wang, Keyu, Lei, Linfeng, Wang, Yixing, Zhuang, Linzhou, and Xu, Zhi
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ELECTROCATALYSTS ,CATALYST poisoning ,HYDROGEN evolution reactions ,CATALYSTS ,OXYGEN evolution reactions ,CATALYSIS ,WATER electrolysis ,POLAR effects (Chemistry) - Abstract
Proton exchange membrane water electrolysis (PEMWE) can be coupled with renewable energy power generation technology and is considered to be a highly promising hydrogen production technology. However, the acidic electrolyte environment, as well as the numerous sulfonic acid groups on the proton exchange membrane surface, can seriously corrode the oxygen evolution reaction (OER) catalyst and even cause deactivation. To develop an efficient acidic OER catalyst, the IrO
x /WO3 heterostructure OER catalyst was prepared by a hydrothermal-calcination method. The coordination environment of IrOx was regulated through the electronic rearrangement effect, improving the OER activity and stability of the catalyst in acidic media. The prepared IrOx /WO3 exhibits excellent OER activity in 0.5 M H2 SO4 , with an overpotential of only 260 mV to achieve a current density of 10 mA cm−2 and a mass activity of 176.8 A gIr −1 . It can stably operate for over 12 hours at a current density of j = 10 mA cm−2 . [ABSTRACT FROM AUTHOR]- Published
- 2024
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9. Function of various levels of hierarchical organization of porous Ce0.9REE0.1O1.95 mixed oxides in catalytic activity.
- Author
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Woźniak, Piotr, Miśta, Włodzimierz, and Małecka, Małgorzata A.
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CATALYTIC activity ,RARE earth oxides ,OXIDES ,CATALYSIS ,IONIC structure ,CATALYSTS ,SOOT - Abstract
In this paper, the effect of the hierarchical arrangement of nanocrystallites on CO oxidation and soot combustion activity has been investigated. Hierarchically structured star-shaped particles (HS stars) were compared with microemulsion-derived, loosely arranged nanoparticles (NPs). Star-like Ce
0.9 REE0.1 O1.95 mixed oxides were synthesized by oxidative thermolysis of Ce0.9 REE0.1 (HCOO)3 mixed formates. The study of the synthesis, structure and catalytic activity of the porous, star-like ceria-based mixed oxides was presented for the first time. It was shown that each level of the hierarchical structure of the star-like mixed oxides has its own functionality and it is vulnerable to modifications. In-depth characterization of as-synthesized ceria allowed determination of the relationship between the hierarchically structured nature of the material and its catalytic activity in CO oxidation and soot combustion. It was concluded that the presence of the 3D structure composed of ceria nanocrystals significantly improves the stability and catalytic activity of the star-like material in comparison to the nanopowder. Moreover, introduction of the trivalent RE ion into the ceria structure led to further improvement of the CO oxidation performance. Finally, the key–lock catalysis concept was applied to explain the enhanced activity of the hierarchically structured star-shaped ceria particles as a catalyst in the soot combustion process in comparison to nanocrystalline CeO2 . [ABSTRACT FROM AUTHOR]- Published
- 2020
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10. Cobalt nanoparticles encapsulated in nitrogen doped graphite as a highly efficient and reusable catalyst for the reduction of 4-nitrophenol.
- Author
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Huang, Yi-Jen, Chen, Yi-Sheng, Xi, Sheng-Yao, Hu, Xun-Wen, and Tsai, Mei-Hui
- Subjects
TRANSITION metal catalysts ,COBALT catalysts ,CATALYSIS ,METAL catalysts ,COBALT ,CATALYSTS ,NITROGEN - Abstract
The present investigation presents a facile approach for synthesizing cobalt nanoparticles encapsulated in nitrogen-doped graphite (Co@NC) for catalytic purposes. The Co@NC composite was employed for the conversion of 4-nitrophenol to 4-aminophenol. Despite the extensive research conducted on the catalytic efficacy of transition metal catalysts, the examination of the cobalt catalyst's durability and reusability over successive reaction cycles remains unexplored. A Co@NC composite catalyst was synthesized using innovative precursors of glucose, urea, and cobalt nitrate. The results demonstrate that the high specific surface area and pore structure of the Co@NC composite catalyst not only have a high adsorption capacity but also accelerate the rate of electron transfer. Due to the synergistic effects of cobaltic metal and nitrogen-doped graphite, the Co@NC catalyst displays remarkable catalytic effects comparable to those of noble metal catalysts. The stable 92% 4-NP conversion rate after 10 reaction cycles also demonstrated the reusability of the composite catalyst. The Co@NC composite catalyst possesses a number of noteworthy characteristics, including excellent recyclability, high stability, and easy magnetic recovery. These characteristics make it a promising option for practical applications in the removal of 4-nitrophenol from industrial water. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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11. Rh-coordinated histidyl bolaamphiphile assembly: a catalyst for the isomerization of cis-stilbene and cis-alkene.
- Author
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Lee, Junsang, Kim, Minji, Lee, Hyesung, and Lee, Sang-Yup
- Subjects
ISOMERIZATION ,CATALYSIS ,CATALYTIC activity ,UNSATURATED fatty acids ,CATALYSTS ,STILBENE ,STILBENE derivatives - Abstract
In this study, we present a colloidal assembly of histidyl bolaamphiphiles whose imidazoles coordinate with rhodium ions (HisC7[Rh]) to exhibit catalytic isomerization activity for cis-stilbene and cis-alkene molecules. The histidyl bolaamphiphiles self-assemble to form a soft scaffold that functions analogously to an apoenzyme. This scaffold exposes multiple histidyl imidazoles and carboxylates on its surface, to which rhodium ions bind, generating catalytically active sites. The Rh coordination with the biochemical functional groups was verified through comprehensive vibrational spectroscopy and calorimetry. The colloidal HisC7[Rh] demonstrated a significant catalytic effect on the isomerization of cis- to trans-stilbene under mild H
2 conditions, resulting in 69% yield of trans-stilbene. In contrast, when Rh(cod)2 BF4 was employed as a control catalyst, only the hydrogenated products of bibenzyl were obtained. These findings underscore the crucial role of histidyl motifs in exhibiting unique catalytic isomerization activity through the coordination with Rh. The catalytic activity of HisC7[Rh] is governed by several factors, such as rhodium content, solvent composition, temperature, and H2 pressure. Moreover, HisC7[Rh] displayed moderate isomerization activity towards not only stilbene but also unsaturated fatty acid isomers, highlighting its expansive potential as an isomerization catalyst. [ABSTRACT FROM AUTHOR]- Published
- 2023
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12. A series of polyoxometalate-based COF composites by one-pot mechanosynthesis of thioether to sulfone.
- Author
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Guo, Yanyan, Liu, Xiaohui, Liu, Xiaodong, Xu, Na, and Wang, Xiuli
- Subjects
CATALYSIS ,POROUS materials ,POLYOXOMETALATES ,CATALYSTS ,SULFONES ,POLYETHERSULFONE ,HOMOGENEITY - Abstract
An effective combination of polyoxometalates (POMs) and porous materials is a feasible method to solve the homogeneity of POMs and synthesize extremely stable POM-based catalysts. Herein, by using simple mechanochemical synthesis, we fabricated a series of composites constructed by Keggin-POMs, p-phenylenediamine (Pa-1), and 1,3,5-triformylphloroglucinol (Tp), which in situ form a stable covalent organic framework (Keggin-POMs@TpPa-1). Notably, the different Keggin-POMs@TpPa-1 composites showed different catalytic effects on thioether oxidation reaction under mild conditions. From the comparison, the catalytic effect of PW
12 @TpPa-1 with its added amount of 27% H3 PW12 O40 is superior to that of other composites, whose catalytic efficiency can reach 99%. This study provides some inspiration for designing diverse POM-modified catalysts with outstanding stability and efficiency using COFs as supports. [ABSTRACT FROM AUTHOR]- Published
- 2023
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13. Keggin heteropolyacid in auto-tandem catalysis: confinement effects over ordered mesoporous silica in the synthesis of 2-pyridones.
- Author
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Galván, Adriana, Damian-Ascencio, Edgar, Martínez, Merced, Domínguez-Esquivel, José Manuel, and Vázquez, Miguel A.
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MESOPOROUS silica ,CATALYSIS ,HYBRID systems ,CATALYSTS ,VOLUMETRIC analysis - Abstract
It is necessary to design and develop simpler, more efficient, and cleaner synthetic methodologies to prepare increasingly complex molecules. One interesting strategy is multicatalysis. The aim of this study was to synthesize a multicatalytic hybrid system by the immobilization of H
3 PW12 O40 (HPW), a polyoxometalate, on ionic liquid-functionalized mesoporous silica (SBA-15 or MCF). The resulting catalysts were characterized by different techniques, including N2 adsorption–desorption, Boehm titration of the acid site, SEM-EDS, FT-IR, XPS, CP-MAS, and NMR. To test the active site acid-oxidant duality of HPW, 2-pyridones were synthesized in a one-pot methodology with auto-tandem catalysis involving the ring-opening/ring-closure/oxidation sequence of 4H-pyrans. The morphology of the support structure affects the duality of HPW. Whereas the MCF complex favors oxidation, the SBA-15 complex favors Brønsted acidity (finding greater oxidation when adding water). The hybrid catalyst was recovered and reused for eight consecutive reaction cycles with no significant loss in activity. [ABSTRACT FROM AUTHOR]- Published
- 2023
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14. Structure-evolved YbBiO3 perovskites for highly formate-selective CO2 electroreduction.
- Author
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Yan, Jiaying, Wang, Xuanyu, Guan, Yayu, Liu, Yuyu, Wang, Linlin, Shao, Qinsi, and Huang, Qiuan
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PEROVSKITE ,ELECTROLYTIC reduction ,CARBON offsetting ,PHOTOCATALYSIS ,SURFACE reconstruction ,CATALYSTS ,CATALYSIS - Abstract
The electrochemical reduction of CO
2 (ERCO2 ) into economically valuable chemicals is one of the most promising ways to achieve carbon neutrality. Perovskite materials have shown potential applications in high-temperature catalysis and photocatalysis due to their unique structure, but their catalytic performance during the aqueous ERCO2 has rarely been investigated. In this study, we developed an efficient YbBiO3 perovskite catalyst (YBO@800) for CO2 conversion to formate, with a maximum faradaic efficiency of 98.3% at −0.9 VRHE , as well as a considerable faradaic efficiency (>90%) over a wide potential range (from −0.8 to −1.2 VRHE ). Further analyses demonstrated that the structural evolution of YBO@800 occurred during the ERCO2 process, and the subsequent construction of the Bi/YbBiO3 heterostructure played a significant role in optimizing the rate-determining step of the ERCO2 . This work inspires the development of perovskite catalysts for the ERCO2 and provides insight into the influence of the surface reconstruction of catalysts on their electrochemical performance. [ABSTRACT FROM AUTHOR]- Published
- 2023
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15. Adsorption-enhanced rapid catalytic degradation of ofloxacin by a CoS2@montmorillonite catalyst via peroxymonosulfate activation.
- Author
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Hong, Peiping, Wu, Lian, Zhao, Yifang, Yu, Yue, Gao, Shuxi, Liao, Bing, and Pang, Hao
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PEROXYMONOSULFATE ,ADSORPTION capacity ,CATALYSTS ,PSEUDOPOTENTIAL method ,CATALYSIS - Abstract
Besides adjusting the active sites, modulating the adsorption capacity and diffusion ability can realize the enrichment of the antibiotics and propel the catalytic degradation properties via the effective contact between active species and antibiotics. Herein, a series of CoS
2 @MMT were prepared by a two-step synthesis. With the synergy of adsorption and catalysis, the obtained composites exhibit potential for the rapid and effective degradation of ofloxacin (OFL) as advanced oxidation process (AOP) catalysts by activating peroxymonosulfate (PMS). Among them, 10CoS2 @MMT can adsorb 41% of OFL and its total removal efficiency of OFL can reach 96.7% within 10 min. Based on the related tests, the composite can decompose OFL through both radical (˙OH, SO4 ˙− , and O2 ˙− ) and non-radical pathways (1 O2 ). The satisfactory catalytic properties and the stability of this kind of composite demonstrate their potential in the practical application of water decontamination. [ABSTRACT FROM AUTHOR]- Published
- 2023
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16. Mechanistic insight into borrowing-hydrogen N-alkylation catalyzed by an MLC catalyst with dual proton-responsive sites.
- Author
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Mei, Lan, Du, Min, Zhang, Yuan, and Hou, Cheng
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CATALYTIC activity ,ACTIVATION energy ,CATALYSTS ,PROTON transfer reactions ,RUTHENIUM compounds ,CATALYSIS ,ALKYLATION - Abstract
Metal–ligand cooperation (MLC) catalysis is one of the most important concepts in the field of organometallic catalysis. However, diverse functional ligands result in ambiguous mechanisms and constrain the understanding of MLC catalysis. Herein, a theoretical study based on DFT calculations is performed to shed light on the mechanistic preference of borrowing-hydrogen N-alkylation catalysed by a ruthenium complex with dual proton-responsive sites. The results suggest that the reaction pathway mediated by the α-NH site requires overcoming a higher activation energy barrier (31.4 kcal mol
−1 ) compared with the γ-NH site due to the ligand distortion after protonation. Nevertheless, the instability caused by the ligand distortion does not transform into catalytic activity for the subsequent hydrogenation reaction. In contrast, the γ-NH site facilitates the rate-determining hydride transfer step (21.1 kcal mol−1 ) via non-covalent interaction instead of participating in the bond formation and breaking process, which is found to be a more plausible mechanism. These findings demonstrate the versatile role of ligand N–H functionality, which may provide useful guidance for the design of new MLC catalysts in the future. [ABSTRACT FROM AUTHOR]- Published
- 2022
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17. Preparation of biacidic tin-based ionic liquid catalysts and their application in catalyzing coupling reaction between ethylene carbonate and dimethyl succinate to synthesize poly(ethylene succinate).
- Author
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Zhao, Xiudan, Guo, Liying, Xu, Tiejun, Wang, Haiyue, Zheng, Rongrong, and Jiang, Zezhong
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ETHYLENE carbonates ,IONIC liquids ,POLYBUTENES ,INTRINSIC viscosity ,CATALYSTS ,CATALYSIS ,POLYETHERSULFONE ,POLYESTERS - Abstract
Three biacidic tin-based functional ionic liquid catalysts were prepared, including [HO
3 S-(CH2 )3 -mim]Cl-SnCl4 , [HOOC-(CH2 )2 -mim]Cl-SnCl4 , and [HO-(CH2 )2 -mim]Cl-SnCl4 . A Fourier transform infrared (FT-IR) spectrometer, a nuclear magnetic resonance instrument (1 H NMR), an X-ray diffractometer (XRD), and a thermal gravimetric analyzer (TGA) were used to test and analyze the structures, molecular structure, crystal structures, and thermal performance of the three catalysts. And investigate their performance in catalyzing the coupling reaction between ethylene carbonate (EC) and dimethyl succinate (DMSu) to synthesize poly(ethylene succinate) (PES). Orthogonal tests were performed to optimize process parameters, explore the effect of polycondensation temperature on the intrinsic viscosity number ([η]) of PES, and discuss the effect of acidic groups on catalytic performance and the mechanism of the catalytic action. An FT-IR spectrometer and a TGA were used for structural characterization and thermal performance tests on polymer PES, and biodegradability tests (enzymolysis tests) on PES. The results showed that the three biacidic tin-based functional ionic liquid catalysts prepared in this study had a satisfactory catalytic effect. Among them, the sulfonic acid imidazole tin-based ionic liquid catalyst ([HO3 S-(CH2 )3 -mim]Cl-SnCl4 ) manifested the best catalytic performance. The catalytic mechanism of the biacidic tin-based ionic liquid catalysts was further explained and discussed. Under the optimal process conditions for the transesterification reaction (temperature: 227 °C; material ratio: EC : DMSu = 1; catalyst consumption: 1.0 wt%; time: 5.5 h), PES had a yield of 67.12%, a selectivity of 82.47%, and an intrinsic viscosity number of [η] = 1.052 dL g−1 , and had good thermal stability and biodegradability. [ABSTRACT FROM AUTHOR]- Published
- 2022
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18. Accelerating electrochemically catalyzed nitrogen reductions using metalloporphyrin-mediated metal–nitrogen-doped carbon (M–N–C) catalysts.
- Author
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Dong, Xinyi, Zhu, Weihua, and Liang, Xu
- Subjects
CATALYSTS ,CATALYTIC activity ,TRANSITION metals ,NITROGEN ,CATALYSIS ,CARBON - Abstract
Herein, a series of transition metal coordinated metalloporphyrin-mediated M–N–C catalysts with single and dual metal atoms were prepared and characterized. Interestingly, these M–N–C catalysts exhibit accelerated N
2 reduction behaviors through electrochemical catalysis. At the potential of E = −0.4V (vs. RHE), the optimum catalyst Fe0.95 Ni0.05 TPP@rGO-800 shows excellent catalytic activity, and the NH3 yield is 22.5 μg mgcat −1 h−1 , which is much higher than that of its single metal counterparts alone, and the faradaic efficiency is as high as 50.7%, which is better than those of most reported catalysts. These results provide an opportunity to further explore the efficient electrochemical synthesis of NH3 from M–N–C materials in the future. [ABSTRACT FROM AUTHOR]- Published
- 2022
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19. SAPO-34 and Zn/ZSM-5 synergistic catalysis of methanol to aromatics from light olefins.
- Author
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Runze Jin, Haobin Hu, Jiaofei Wang, Zhuangzhuang Zhang, Chengyi Dai, and Xiaoxun Ma
- Subjects
ALKENES ,CATALYSIS ,AROMATIZATION ,CATALYSTS ,ATOMS ,METHANOL - Abstract
The traditional one-step reaction of methanol to aromatics on ZSM-5 is a potential route for the synthesis of non-petroleum aromatics. Zn/ZSM-5 is widely used as the most common catalyst for the methanol to aromatics reaction. However, due to the generation of by-products such as alkanes, carbon atoms are consumed, and it is still difficult to obtain high aromatic selectivity. In this work, in order to improve the aromatic selectivity, the traditional one-step reaction is divided into two steps: methanol to light olefins and aromatization of light olefins. SAPO-34 and Zn/ZSM-5 are designed as catalysts for the above two-step reaction respectively. Through a study of the loading methods and loading ratios of the above two catalysts, it is found that the top-down loading mode of SAPO-34 and Zn/ZSM-5 can obtain higher aromatic selectivity than the one-step reaction. The reason for the improvement of aromatic selectivity is that the light olefins generated by SAPO-34, as the intermediate of methanol aromatization, promote the generation of aromatics on the Zn/ZSM-5 catalyst. The acidity and reaction temperature of the two catalysts are further optimized to improve the reaction performance. Under the conditions of 673 K and a loading ratio of SAPO-34 to Zn/ZSM-5 of 1 : 9, the selectivity of aromatics and BTX in the two-step reaction can reach 80.0% and 56.7% respectively. It is much higher than 64.9% and 32.0% in the one-step reaction by filling Zn/ZSM-5 only. This reaction method provides a new way for the production of aromatics and BTX and shows great development potential. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
20. Porous MoS2 nanosheets for the fast decomposition of energetic compounds.
- Author
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Zhao, Xu, Zhang, Jianhu, Gong, Feiyan, Huang, Bin, and Yang, Zhijian
- Subjects
CATALYSIS ,NANOSTRUCTURED materials ,PROPELLANTS ,MOLYBDENUM disulfide ,CATALYSTS - Abstract
The energy release performance of energetic compounds like 3-nitro-1,2,4-trizole-5-one (NTO) and 5,5′-bistetrazole-1,1′-diolate (TKX-50) are indispensable in propellent formulations. However, thermal decomposition behavior is impeded by unfavorable catalysts. Presently, ultrathin porous MoS
2 nanosheets (pMoS2 ) are considered as high-performance catalysts for NTO and TKX-50 decomposition. The pMoS2 in 5 wt% content could decrease the decomposition temperature of NTO and TKX-50 by 13.5 °C and 37.1 °C, respectively. Furthermore, the exothermic heat-release for pMoS2 @NTO and pMoS2 @TKX-50 were increased almost by a factor of two. The porous structure combined with large specific area of pMoS2 could mostly trigger the catalytic effect towards energetic compound decomposition. Additionally, the as-obtained MoS2 endowed advances in safety performance of NTO and TKX-50, with remarkably reduced impact and friction sensitivity. The as-proposed strategy may stimulate a different perspective towards the fast decomposition of energetic materials in propellants. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
21. Selective catalysis in a cellular microenvironment—a living cell catalytic system with intracellular nanopalladium for olefin hydrogenation.
- Author
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Liu, Peng, Ru, Xiangli, Chang, Yi, Ma, Nana, Li, Ge, Chen, Huifeng, Ren, Xueqing, Bai, Zhengyu, Ma, Xiaoming, and Yang, Lin
- Subjects
ALKENES ,CHEMICAL amplification ,BIOMIMETIC synthesis ,CATALYTIC hydrogenation ,CATALYSIS ,PALLADIUM catalysts ,CATALYSTS - Abstract
The selectivity of metal nanocatalysts is critical to chemical transformations and industries. Herein, a highly selective heterogeneous living cell catalytic system (LCCS) with intracellular Pd nanodots (bio-nPd) via in situ biomimetic synthesis is constructed. Research studies show that the LCCS is capable of size-selective catalytic hydrogenation for a series of acrylamides in water under mild conditions, and has self-reproducible, reusable and recyclable performance. Moreover, the LCCS also has high catalytic activity: the turnover frequency (TOF) for the acrylamide is up to 198.3 h
−1 and the conversion rate is 100%. The calculation results show that the size-selectivity is closely interrelated with the inherent "gating" effect of the cell membrane, which is beneficial for the entry of small molecules. The highly selective and eco-friendly characteristics of the catalytic systems provide an effective strategy for exploring novel catalytic systems that can meet the requirements of sustainable development. [ABSTRACT FROM AUTHOR]- Published
- 2022
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- View/download PDF
22. Adaptive water oxidation catalysis on a carboxylate-sulfonate ligand with low onset potential.
- Author
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Yang, Jing, Zhan, Shaoqi, Wang, Linqin, Yang, Hao, Duan, Lele, Fan, Xiaolei, Liu, Tianqi, and Sun, Licheng
- Subjects
OXIDATION of water ,LIGANDS (Chemistry) ,CATALYSIS ,CATALYSTS ,CARBOXYLATES ,COORDINATION polymers - Abstract
A water oxidation catalyst Ru-bcs (bcs = 2,2′-bipyridine-6′-carboxylate-6-sulfonate) with a hybrid ligand was reported. Ru-bcs utilizes the electron-donating properties of carboxylate ligands and the on-demand coordination feature of sulfonate ligands to enable a low onset potential of 1.21 V vs. NHE and a high TOF over 1000 s
−1 at pH 7. The adaptive chemistry uncovered in this work provides new perspectives for developing molecular catalysts with high efficiency under low driving forces. [ABSTRACT FROM AUTHOR]- Published
- 2024
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23. Enhanced photocatalytic nitrogen fixation in BiVO4: constructing oxygen vacancies and promoting electron transfer through Ohmic contact.
- Author
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Wang, Libo, Li, Mohan, Wang, Shiyu, Zhang, Tingting, Li, Fengyan, and Xu, Lin
- Subjects
OHMIC contacts ,NITROGEN fixation ,CHARGE exchange ,CATALYSTS ,CATALYSIS ,SURFACE plasmon resonance ,ENERGY shortages - Abstract
The problem of energy crisis promotes the development and utilization of materials related to the application of solar energy. Employing solar energy for clean photocatalytic nitrogen fixation is an effective approach to replace the high-energy consumption Haber–Bosch nitrogen fixation method to alleviate the energy crisis. In this article, mulberry-like BiVO
4 containing oxygen vacancies (OVs–BVO) was prepared by the solvothermal method. In order to further elevate the catalytic effect of the catalyst, Ag nanoparticles with uniform distribution were loaded on the surface of OVs–BVO by the photodeposition method. A variety of survey techniques were performed to characterize the properties of the materials, including XRD, SEM, TEM, Raman, XPS, EPR, DRS, PL and Kelvin probe study. The results show that the subband (defect level) generated by the presence of OVs can accommodate low energy electrons to activate the adsorbed N2 . Ag nanoparticles firmly attached on the surface of OVs–BVO produced a strong local surface plasmon resonance (LSPR) effect, which promoted the utilization of light energy and the effective separation of electron–hole pairs. The electrons have no interfacial barrier to overcome during the transfer between Ag and BVO due to their Ohmic contact. The application of Ag loaded OVs–BVO as a catalyst provides a new direction for the study of catalysts in the field of photocatalytic nitrogen fixation. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
24. High-efficacy glycerol acetalization with silica gel immobilized Brønsted acid ionic liquid catalysts—preparation and comprehending the counter-anion effect on the catalytic activity.
- Author
-
Shashni, Shalini, Singh, Vasundhara, and Toor, Amrit Pal
- Subjects
CATALYSIS ,CATALYTIC activity ,SILICA gel ,BRONSTED acids ,CATALYSTS ,HETEROGENEOUS catalysts ,GLYCERIN ,ZWITTERIONS - Abstract
Imidazolium sulfonate zwitterions (ZIs) with unconventional counter-anions were used to fabricate a series of mesoporous silica-gel-immobilized Brønsted acid ionic liquid (SG@BAIL) nanocatalysts. In comparison to traditional heterogeneous catalysts, these immobilised heterogeneous catalysts have the advantage of ionic-liquid acidic sites and the advantage of solid silica gel as a support, increasing their catalytic activities. The catalysts were analysed using a series of physicochemical techniques and their catalytic efficiencies were evaluated during the acetalization of glycerol (G) with benzaldehyde (B). The influence of the counter-anions present in the SG@BAIL catalysts was initially investigated in terms of the percentage conversion vs. the reaction time at a particular temperature. Furthermore, different parametric studies relating to the acetalization reaction were carried out based on the catalyst with the maximum activity. SG-[C
3 ImC3 SO3 H][OTf] was observed to have the highest catalytic performance and durability during ecofriendly acetal synthesis, with the highest selectivity for 1,3-dioxane. Parametric studies of the acetalization reaction were carried out, and the catalyst showed noteworthy performance at 90 °C, showing 94% conversion in an equimolar reactant mixture under solvent-free conditions with 0.03 wt% catalyst loading in a short time span of 75 min. In addition, kinetics modelling was performed using reversible second-order kinetics to calculate the forward rate constants at various temperatures. The activation energy of the reaction was determined using the Arrhenius equation, and the overall activation energy was 69.33 kJ mol−1 . These investigations have demonstrated the excellent potential of SG@BAIL catalysts for practical application in the glycerol acetalization process. [ABSTRACT FROM AUTHOR]- Published
- 2021
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25. Catalysis of CO2 reduction by diazapyridinophane complexes of Fe, Co, and Ni: CO2 binding triggered by combined frontier MO associations involving a SOMO.
- Author
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Sakaguchi, Yuto, Call, Arnau, Yamauchi, Kosei, and Sakai, Ken
- Subjects
CATALYSTS ,CATALYSIS ,OXIDATIVE addition ,CHARGE exchange ,NICKEL catalysts - Abstract
Our previous study on the photochemical CO
2 reduction into CO catalyzed by the diazapyridinophane complexes of Fe, Co, and Ni revealed that (i) the Co catalyst shows the highest TOF but degrades rapidly, (ii) the Fe catalyst exhibits a lower TOF relative to Co but shows higher robustness, giving a higher TON, and (iii) the Ni complex shows no activity (Sakaguchi et al., Chem. Commun., 2019, 55, 8552). Here we show our DFT results unveiling that the Fe and Co catalysts can utilize multiple sets of frontier MO associations at the CO2 binding by including one of the SOMOs in a high-spin d7 Fe(I) and d8 Co(I) center, respectively, giving an increased driving force for these oxidative addition steps. Remarkably, two-electron reduction of CO2 to CO2 2− at the binding step is driven by the two electrons transferred from different d-based orbitals. The CoI species binds CO2 at the rate-limiting step with an activation barrier of 15.0 kcal mol−1 , rationalizing the high initial TOF observed. However, the CoI (CO) species is given as a dead-end product, consistent with its relatively rapid deactivation. The Fe catalyst possesses a slightly higher barrier in CO2 binding (ΔG‡ = 15.8 kcal mol−1 ) but does not stabilize the FeI (CO) species which readily releases CO (ΔG = 3.5 kcal mol−1 ). The Ni catalyst has the smallest barrier in CO2 binding (ΔG‡ = 11.5 kcal mol−1 ) but the CO release is largely prohibited by the dead-end NiI (CO) species, consistent with its inactive character towards CO2 reduction. The combined results all satisfactorily explain the observed catalytic behaviors. [ABSTRACT FROM AUTHOR]- Published
- 2021
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26. Metal-free hydrogen evolution cross-coupling enabled by synergistic photoredox and polarity reversal catalysis.
- Author
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Cao, Jilei, Yang, Xiaona, Ma, Lishuang, Lu, Kanghui, and Zhou, Rong
- Subjects
HYDROGEN evolution reactions ,CATALYSTS ,CATALYSIS ,HYDROGEN ,METALS ,SILANOLS ,FUNCTIONAL groups - Abstract
A synergistic combination of photoredox and polarity reversal catalysis enabled a hydrogen evolution cross-coupling of silanes with H
2 O, alcohols, phenols, and silanols, which afforded the corresponding silanols, monosilyl ethers, and disilyl ethers, respectively, in moderate to excellent yields. The dehydrogenative cross-coupling of Si–H and O–H proceeded smoothly with broad substrate scope and good functional group compatibility in the presence of only an organophotocatalyst 4-CzIPN and a thiol HAT catalyst, without the requirement of any metals, external oxidants and proton reductants, which is distinct from the previously reported photocatalytic hydrogen evolution cross-coupling reactions where a proton reduction cocatalyst such as a cobalt complex is generally required. Mechanistically, a silyl cation intermediate is generated to facilitate the cross-coupling reaction, which therefore represents an unprecedented approach for the generation of silyl cation via visible-light photoredox catalysis. [ABSTRACT FROM AUTHOR]- Published
- 2021
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27. Magneli-type tungsten oxide nanorods as catalysts for the selective oxidation of organic sulfides.
- Author
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Dören, René, Hartmann, Jens, Leibauer, Benjamin, Panthöfer, Martin, Mondeshki, Mihail, and Tremel, Wolfgang
- Subjects
TUNGSTEN oxides ,CATALYSIS ,CATALYSTS ,ENVIRONMENTAL chemistry ,SULFOXIDES ,OXIDATION ,NANORODS ,TUNGSTEN trioxide - Abstract
Selective oxidation of thioethers is an important reaction to obtain sulfoxides as synthetic intermediates for applications in the chemical industry, medicinal chemistry and biology or the destruction of warfare agents. The reduced Magneli-type tungsten oxide WO
3−x possesses a unique oxidase-like activity which facilitates the oxidation of thioethers to the corresponding sulfoxides. More than 90% of the model system methylphenylsulfide could be converted to the sulfoxide with a selectivity of 98% at room temperature within 30 minutes, whereas oxidation to the corresponding sulfone was on a time scale of days. The concentration of the catalyst had a significant impact on the reaction rate. Reasonable catalytic effects were also observed for the selective oxidation of various organic sulfides with different substituents. The WO3−x nanocatalysts could be recycled at least 5 times without decrease in activity. We propose a metal oxide-catalyzed route based on the clean oxidant hydrogen peroxide. Compared to other molecular or enzyme catalysts the WO3−x system is a more robust redox-nanocatalyst, which is not susceptible to decomposition or denaturation under standard conditions. The unique oxidase-like activity of WO3−x can be used for a wide range of applications in synthetic, environmental or medicinal chemistry. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
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28. Exploration of benign deep eutectic solvent–water systems for the highly efficient production of furfurylamine from sugarcane bagasse via chemoenzymatic cascade catalysis.
- Author
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Li, Qing, Di, Junhua, Liao, Xiaolong, Ni, Jiacheng, Li, Qi, He, Yu-Cai, and Ma, Cuiluan
- Subjects
CATALYSTS ,EUTECTIC reactions ,BAGASSE ,SUGARCANE ,CATALYSIS ,EUTECTICS ,BIOMASS chemicals ,BIOCATALYSIS - Abstract
Recently, cost-effective production of high value-added furan chemicals from abundant and renewable bioresources has attracted much attention via a chemoenzymatic approach in an environmentally friendly reaction system. In this work, a chemoenzymatic cascade reaction for bridging tandem chemocatalysis and biocatalysis was constructed to valorize biomass into furfurylamine in a deep eutectic solvent (DES)–water system. Waste shrimp shell (SS) was used as a biobased carrier to prepare sulfonated tin-based solid acid (Sn-SS) for catalyzing sugarcane bagasse (SB) into furfural in DES–water. The prepared Sn-SS was characterized by XRD, SEM, FTIR spectroscopy and BET. Furfural (113.2 mM) was obtained in 62.3% yield from xylan in SB by Sn-SS (0.6 wt% dose) within 20 min at 170 °C in [ChCl][EG]–water (20 : 80, v : v). A potential catalytic mechanism was proposed for catalyzing SB into FAL and derivatives in [ChCl][EG]–water. Sequentially, one newly constructed recombinant Escherichia coli PRSFDuet-CV-AlaDH cells containing ω-transaminase and L -alanine dehydrogenase were used for the biological transamination of SB-derived furfural to furfurylamine in the presence of amine donor NH
4 Cl (2.0 mol NH4 Cl/mol furfural) and cosubstrate glucose (1.0 mol glucose/mol furfural) at 35 °C and pH 8.0 without the removal of Sn-SS and residual SB. Within 1 h, SB-derived furfural was wholly aminated to furfurylamine with a productivity of 0.458 g furfurylamine per g xylan in SB by whole cells using NH4 Cl as an amine donor in [ChCl][EG]–water (20 : 80, v : v). It was found that [ChCl][EG]–water enhanced furfural and furfurylamine yields. Compared to the aqueous system, this green [ChCl][EG]–water (20 : 80, v : v) system enabled the highly efficient production of furfurylamine from SB via chemoenzymatic cascade catalysis with a sulfonated Sn-SS catalyst and ω-transaminase biocatalyst by enhancing the catalytic activity and thermostability of chemocatalysts and biocatalysts. This chemoenzymatic cascade reaction strategy had potential application for utilizing renewable biomass into furan-based chemicals in the benign DES–water system. [ABSTRACT FROM AUTHOR]- Published
- 2021
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29. Direct oxidative carboxylation of terminal olefins to cyclic carbonates by tungstate assisted-tandem catalysis.
- Author
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Calmanti, Roberto, Selva, Maurizio, and Perosa, Alvise
- Subjects
CATALYSTS ,CATALYSIS ,CARBOXYLATION ,TUNGSTATES ,ALKENES ,CARBONATES ,CATALYTIC activity - Abstract
Tungstate catalysts are well established for olefin epoxidation reactions, while their catalytic activity for CO
2 insertion in epoxides is a more recent discovery. This dual reactivity of tungstate prompted the present development of a catalytic tandem process for the direct conversion of olefins into the corresponding cyclic organic carbonates (COCs). Each of the two steps was studied in the presence of the ammonium tungstate ionic liquid catalyst – [N8,8,8,1 ]2 [WO4 ] – obtained via a benign procedure starting from ammonium methylcarbonate ionic liquids. The catalytic epoxidation first step was optimised on 1-decene as model substrate, using H2 O2 as benign oxidant, [N8,8,8,1 ]2 [WO4 ] as catalyst and phosphoric acid as promoter affording quantitative conversion with 92% selectivity towards decene oxide. Unfortunately, the addition of CO2 from the start (auto-tandem catalysis) gave low yields of decene carbonate (<10%). On the contrary, the addition of 1 atm CO2 and tetrabutyl ammonium iodide after completion of the epoxidation first step without any intermediate work-up (assisted-tandem catalysis) afforded a 94% yield in decene carbonate. The protocol could be scaled up to a 10 gram scale. The scope of the reaction was demonstrated for primary aliphatic olefins with different alkyl chain lengths (C6 –C16 ), while cyclic and aromatic activated olefins such as cyclohexene and styrene suffered from the formation of undesired overoxidation products in the first step. [ABSTRACT FROM AUTHOR]- Published
- 2021
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30. 14-Electron Rh and Ir silylphosphine complexes and their catalytic activity in alkene functionalization with hydrosilanes.
- Author
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Abeynayake, Niroshani S., Zamora-Moreno, Julio, Gorla, Saidulu, Donnadieu, Bruno, Muñoz-Hernández, Miguel A., and Montiel-Palma, Virginia
- Subjects
CATALYTIC activity ,ISOMERS ,CATALYSIS ,HEXENE ,HYDROSILYLATION ,CATALYSTS ,RHODIUM catalysts - Abstract
Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh(III) devoid of agostic interactions. The complexes [X–Rh(κ
3 (P,Si,Si)PhP(o-C6 H4 CH2 Sii Pr2 )2 ], where X = Cl (Rh-1), Br (Rh-2), I (Rh-3), OTf (Rh-4), Cl·GaCl3 (Rh-5); derive from a bis(silyl)-o-tolylphosphine with isopropyl substituents on the Si atoms. All five complexes display a sawhorse geometry around Rh and exhibit similar spectroscopic and structural properties. The catalytic activity of these complexes and [Cl–Ir(κ3 (P,Si,Si)PhP(o-C6 H4 CH2 Sii Pr2 )2 ], Ir-1, in styrene and aliphatic alkene functionalizations with hydrosilanes is disclosed. We show that Rh-1 catalyzes effectively the dehydrogenative silylation of styrene with Et3 SiH in toluene while it leads to hydrosilylation products in acetonitrile. Rh-1 is an excellent catalyst in the sequential isomerization/hydrosilylation of terminal and remote aliphatic alkenes with Et3 SiH including hexene isomers, leading efficiently and selectively to the terminal anti-Markonikov hydrosilylation product in all cases. With aliphatic alkenes, no hydrogenation products are observed. Conversely, catalysis of the same hexene isomers by Ir-1 renders allyl silanes, the tandem isomerization/dehydrogenative silylation products. A mechanistic proposal is made to explain the catalysis with these M(III) complexes. [ABSTRACT FROM AUTHOR]- Published
- 2021
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31. Ensemble effects on allylic oxidation within explicit solvation environments.
- Author
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Le, Hung M., Guagliardo, Mariano, Gorden, Anne E. V., and Clark, Aurora E.
- Subjects
CYCLOHEXENE ,MOLECULAR theory ,CATALYSTS ,DENSITY functional theory ,SOLVATION ,MOLECULAR dynamics ,OXIDATION ,CATALYSIS - Abstract
Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene using a Cu(II) 7-amino-6-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile to create cyclohexenone and H
2 O as products. After the initial H-atom abstraction step, two different reaction pathways have been identified that are distinguished by the participation of alkyl hydroperoxide (referred to as the "open" cycle) versus the methanol side-product (referred to as the "closed" cycle) within the catalyst recovery process. Importantly, both pathways involve dehydrogenation and re-hydrogenation of the –NH2 group bound to the Cu-site – a feature that is revealed from the ensemble sampling of configurations of the reactive species that are stabilized within the explicit solvent environment of the simulation. Estimation of the energy span from the experimental turnover frequency yields an approximate value of 22.7 kcal mol−1 at 350 K. Whereas the closed cycle value is predicted to be 26.2 kcal mol−1 , the open cycle value at 16.5 kcal mol−1 . Both pathways are further consistent with the equilibrium between Cu(II) and Cu(III) that has previously been observed. In comparison to prior static DFT calculations, the ensemble of both solute and solvent configurations has helped to reveal a breadth of processes that underpin the full catalytic cycle yielding a more comprehensive understanding of the importance of radical reactions and catalysis recovery. [ABSTRACT FROM AUTHOR]- Published
- 2021
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32. A paradigm for the efficient synthesis of bio-based polycarbonate with deep eutectic solvents as catalysts by inhibiting the degradation of molecular chains.
- Author
-
Wang, Weiwei, Yang, Zifeng, Zhang, Yaqin, He, Hongyan, Fang, Wenjuan, Zhang, Zhencai, and Xu, Fei
- Subjects
EUTECTICS ,MOLECULAR weights ,POLYCARBONATES ,FOURIER transform infrared spectroscopy ,CATALYSIS ,CATALYSTS - Abstract
In this study, an efficient catalytic system composed of deep eutectic solvents (DESs) was developed by adjusting the basicity of hydrogen bond donors (HBDs) to synthesize poly(isosorbide) carbonate (PIC) with high weight average molecular weight (M
w ). It was demonstrated that the Mw of PIC prepared by using nearly neutral [EminOH]Cl–2EG was the highest. The results of the transesterification kinetics with different catalysts supported that the transesterification rate was significantly promoted as the basicity of DESs increased but their strong alkalinity inhibited the Mw of PIC. Therefore, the degradation of PIC was investigated to reveal the mechanism of the influence of basicity on the molecular weight of PIC. The strong alkalinity of DESs would cause the depolymerization of the macromolecular chains and ultimately limit the molecular weight of the product, proving the experimental fact that a near-neutral catalyst was more conducive to the Mw of PIC. Finally, a reasonable mechanism of synergistic catalysis was proposed based on1 H NMR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and experimental results. The metal-free, low-cost, high catalytic activity DES catalyst involved here is a practical candidate for advanced bio-based polycarbonate. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
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33. Visible light-promoted synthesis of pyrrolidinone derivatives via Rose Bengal as a photoredox catalyst and their photophysical studies.
- Author
-
Dutta, Arup, Rohman, Mostofa A., Nongrum, Ridaphun, Thongni, Aiborlang, Mitra, Sivaprasad, and Nongkhlaw, Rishanlang
- Subjects
ROSE bengal ,CHEMICAL synthesis ,FLUORESCENCE spectroscopy ,CATALYSTS ,CATALYSIS ,TIME-resolved spectroscopy ,INTRAMOLECULAR catalysis - Abstract
Herein, we report an intramolecular radical cyclization reaction towards the synthesis of pyrrolidinone derivatives via metal-free photoredox catalysis under irradiation from blue LEDs. Some of the remarkable features of this protocol include synthetic efficiency, green reaction profile, easy isolation of products and short reaction time. The photophysical properties of synthesized compounds were investigated via steady state and time-resolved fluorescence spectroscopy in the solid state. Results showed the promising opportunity for their spectral tuning together with large Stokes-shifted and highly active fluorescence emission, thus indicating that these molecular scaffolds can be effective probes for the biological applications and development of opto-electronic devices. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
34. Air-stable and reusable nickel phosphide nanoparticle catalyst for the highly selective hydrogenation of D-glucose to D-sorbitol.
- Author
-
Yamaguchi, Sho, Fujita, Shu, Nakajima, Kiyotaka, Yamazoe, Seiji, Yamasaki, Jun, Mizugaki, Tomoo, and Mitsudome, Takato
- Subjects
NICKEL phosphide ,SORBITOL ,METAL catalysts ,CATALYSTS ,HYDROGENATION ,CATALYSIS ,MAGNETIC nanoparticles ,POLYOLS - Abstract
The hydrogenation of carbohydrates to polyols is an industrially important process, but it requires air-unstable, non-noble metal catalysts with low activity and harsh reaction conditions. Herein, we report a hydrotalcite (HT)-supported nickel phosphide nanoparticle (nano-Ni
2 P/HT) that exhibits both air stability and high activity for the selective hydrogenation of D -glucose to D -sorbitol in water. The nano-Ni2 P/HT catalyst provides D -sorbitol in excellent yield with >99% selectivity under mild reaction conditions, and is the first non-noble metal catalyst that can operate under just 1 bar of H2 or at ambient temperature. This high-performance nano-Ni2 P/HT catalyst is significantly different from conventional Ni(0) and NiO nanoparticles and Raney catalysts, which result in almost no production of D -sorbitol, demonstrating the unique catalysis of nano-Ni2 P/HT. Furthermore, nano-Ni2 P/HT shows the highest activity among those reported for non-noble metal catalysts. The nano-Ni2 P/HT catalyst can also be reused without sacrificing its high activity and selectivity. Additionally, the successful transformation of a concentrated D -glucose solution (50 wt%) to D -sorbitol has been achieved. This is the first example of an air-stable, highly active, and reusable non-noble metal catalyst that can replace conventional catalysts used for D -sorbitol production, thus providing a cheap, green, and sustainable route for this process. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
35. An efficient and recyclable Pickering magnetic interface biocatalyst: application in biodiesel production.
- Author
-
Liu, Xiaobo, Mao, Yuhua, Yu, Siyang, Zhang, Hao, Hu, Kecheng, Zhu, Lingyu, Ji, Jianbing, and Wang, Jianli
- Subjects
ENZYMES ,BIOCATALYSIS ,SOY oil ,BASE catalysts ,CATALYSIS ,CATALYTIC activity ,CATALYSTS - Abstract
Green and efficient catalysts for the production of biodiesel are highly important. In this study, a Pickering magnetic interface biocatalyst (Fe
3 O4 @PS-NH-lipase) was prepared, which can effectively stabilize the soybean oil-in-methanol emulsion and achieve static transesterification. When the appropriate methanol/soybean oil molar ratio and catalyst loading were chosen, the Pickering interface biocatalyst exhibited outstanding enzymatic activity, reaching a conversion rate of 89.3% after 30 h. Pickering interfacial catalysis (PIC, immobilizing catalytic centers on a carrier and combining it with a Pickering emulsion) shows more significant specific activity, leading to a 1.2-fold improvement in catalytic performance as compared to Pickering assisted catalysis (PAC, relying on the use of nanoparticles for stabilizing Pickering emulsions together with a homogeneous catalyst). Moreover, the recycled catalyst still possesses significant catalytic activity after 5 cycles. This article provides a green and efficient strategy for the effective recovery of biologically active substances and the enhancement of biphasic reactions. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
36. A general protocol for the synthesis of Pt-NHC (NHC = N-heterocyclic carbene) hydrosilylation catalysts.
- Author
-
Maliszewski, Benon P., Tzouras, Nikolaos V., Guillet, Sébastien G., Saab, Marina, Beliš, Marek, Van Hecke, Kristof, Nahra, Fady, and Nolan, Steven P.
- Subjects
HYDROSILYLATION ,CARBENE synthesis ,DIMETHYL sulfide ,HETEROCYCLIC chemistry ,CATALYSTS ,CATALYSIS - Abstract
A general, user-friendly synthetic route to [Pt(NHC)(L)Cl
2 ] and [Pt(NHC)(dvtms)] (L = DMS, Py; DMS = dimethyl sulfide, dvtms = divinyltetramethylsiloxane, Py = pyridine) complexes has been developed. The procedure is applicable to a wide range of ligands and enables facile synthetic access to key Pt(0)- and Pt(II)-NHC complexes used in hydrosilylation catalysis. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
37. New cobalt(II) coordination designs and the influence of varying chelate characters, ligand charges and incorporated group I metal ions on enzyme-like oxidative coupling activity.
- Author
-
Oloyede, Hammed Olawale, Woods, Joseph Anthony Orighomisan, Görls, Helmar, Plass, Winfried, and Eseola, Abiodun Omokehinde
- Subjects
OXIDATIVE coupling ,METAL ions ,CATALYSTS ,COBALT ,CATALYSIS ,MASS spectrometry ,LIGANDS (Chemistry) ,CHELATING agents - Abstract
In transition-metal-mediated catalysis, designing new, well defined coordination architectures and subjecting them to catalysis testing under the same reaction conditions is a necessary tool for gaining an improved understanding of desirable active site geometries and characteristics. In this work, three ligands varying in chelation and charge characters (1 = tridentate, dianionic N^N^N; 2 = bidentate, dianionic N^N; 3 = bidentate, neutral N^O) were synthesized and introduced as organic backbones around cobalt(II) centres. Four multinuclear coordination assemblies incorporating various group I metal ions (i.e., (Na-Co1-i)
2 , (Na-Co1-e)2 , (K-Co1-e)2 and (Cs-Co1-e)2 ) and two mononuclear complexes (i.e., Co2 and Co3) were isolated, structurally characterized and studied as phenoxazinone synthase models. X-ray data and Continuous Shape Measure (CShM) calculations described unusual vacant trigonal bipyramidal geometries for (Na-Co1-i)2 , (Na-Co1-e)2 and Co3, trigonal bipyramids for (K-Co1-e)2 and (Cs-Co1-e)2 , and a tetrahedron for Co2. According to mass spectrometry data, the four multinuclear (MI -Co1-solvate)2 complexes of ligand 1 easily dissociate in solution to yield the corresponding ions including a common mononuclear Co1 unit. Testing as models in the oxidative coupling of o-aminophenol revealed that an increasing chelate character of the organic ligand backbone produces an undesirable catalyst activity reduction. Furthermore, the similarity in coupling efficiencies observed among complexes (Na-Co1-i)2 , (Na-Co1-e)2 , (K-Co1-e)2 and (Cs-Co1-e)2 proves that the presence of varying group I metal ions contributed no catalytic effects to the coupling efficiencies and that the Co1 species, which is generated by dissociation in solution, is the only active species responsible for the observed biomimetic behaviours. Therefore, the combination of anionic chelate ligands with easily detachable, neutral co-ligands (e.g., water or pyridine) around a cobalt(II) centre could be recommended for the generation of a successful catalyst material, rather than the combination of a neutral chelate ligand with counter-anionic monodentate co-ligands like halides. [ABSTRACT FROM AUTHOR]- Published
- 2020
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- View/download PDF
38. Novel CoNi-metal–organic framework crystal-derived CoNi@C: synthesis and effective cascade catalysis.
- Author
-
Wang, Lin, Zhang, Jian-Wei, Li, Chenchen, Sun, Jia-Lu, Wang, Guo-Ming, and Chen, Yu-Zhen
- Subjects
CATALYTIC dehydrogenation ,CATALYSIS ,METAL catalysts ,METAL-organic frameworks ,CATALYSTS ,INDUSTRIAL metals - Abstract
Evaluating the catalytic influence of metal sites on derivates obtained from the calcination of metal–organic frameworks (MOFs) is very important for the rational construction of novel MOFs. Based on this catalytic functional guidance, two new Co-MOF and CoNi-MOF crystals were designed and synthesized, and further pyrolyzed to obtain corresponding porous carbon-based catalysts. Interestingly, the derivates exhibited better catalytic performance toward the tandem reaction of dehydrogenation of NH
3 BH3 and subsequent hydrogenation reduction of nitro/olefin compounds than those of the CoNi-ZIF (a star MOF)-derived CoNi@carbon and most metal catalysts. Significantly, the CoNi@C maintained excellent activity, even after 30 cycles, demonstrating its great longevity and durability, which are especially important for the practical application of metal catalysts in industrial catalysis. [ABSTRACT FROM AUTHOR]- Published
- 2020
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- View/download PDF
39. Product inhibition in nucleophilic aromatic substitution through DPPPent-supported π-arene catalysis.
- Author
-
Mueller, Benjamin R. J. and Schley, Nathan D.
- Subjects
CATALYSIS ,CATALYSTS ,INHIBITION (Chemistry) ,THERMODYNAMICS ,RUTHENIUM ,MORPHOLINE - Abstract
Nucleophilic aromatic substitution (S
N Ar) of fluorobenzene by morpholine at a bis(diphenylphosphino)pentane-supported ruthenim complex is investigated as a model system for π-arene catalysis through the synthesis and full characterization of proposed intermediates. The SN Ar step proceeds quickly at room temperature, however the product N-phenylmorpholine binds tightly to the ruthenium ion. In the case examined, the thermodynamics of arene binding favor product N-phenylmorpholine over fluorobenzene binding by a factor of 2000, corresponding to significant product inhibition. Observations of the catalyst resting state support this hypothesis and demonstrate an additive-controlled role for a previously-proposed ligand cyclometalation. [ABSTRACT FROM AUTHOR]- Published
- 2020
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- View/download PDF
40. Single-phase catalysis for reductive etherification of diesel bioblendstocks.
- Author
-
Hafenstine, Glenn R., Huq, Nabila A., Conklin, Davis R., Wiatrowski, Matthew R., Huo, Xiangchen, Guo, Qianying, Unocic, Kinga A., and Vardon, Derek R.
- Subjects
PRECIPITATION (Chemistry) ,CATALYST poisoning ,CATALYSIS ,ETHERIFICATION ,CONTINUOUS flow reactors ,CATALYSTS ,CATALYST supports - Abstract
Reductive etherification is a promising catalytic chemistry for coupling biomass derived alcohols and ketones to produce branched ethers that can be used as high cetane, low sooting blendstocks for diesel fuel applications. Previous catalyst materials examined for reductive etherification have typically been limited to binary physical mixtures of metal hydrogenation and acidic acetalization catalysts with limited thermal stability and industrial applicability. To address this, we developed a single-phase catalyst comprising Pd supported on acidic metal oxides with high catalytic activity, product selectivity, and regeneration stability. Batch reactor screening identified niobium phosphate (NbOPO
4 ) as the most active acidic metal oxide catalyst support, which was downselected to synthesize single-phase catalysts by Pd loading. Several branched ethers with favourable fuel properties were synthesized to demonstrate broad catalyst applicability. The fresh Pd/NbOPO4 catalyst displayed a surface area of 130 m2 g−1 , high acidity of 324 μmol g−1 and Pd dispersion of 7.8%. The use of acidic metal oxide support allowed for elevated reaction temperatures with a mass selectivity to 4-butoxyheptane of 81% at 190 °C and an apparent activation energy of 40 kJ mol−1 . Continuous flow reactor testing demonstrated steady catalyst deactivation due to coke formation of 10 wt% after 117 h of time-on-stream. Four simulated catalyst regeneration cycles led to small changes in surface area and total acidity; however, a decrease in Pd site density from 18 to 8 μmol g−1 , in combination with an apparent Pd nanoparticle size effect, caused an increase in the production rate of 4-butoxyheptane from 138 to 190 μmol gcat −1 min−1 with the regenerated catalyst. Lastly, technoeconomic analysis showed that higher H2 equivalents and lower weight hourly space velocity values can reduce ether catalytic production costs. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
41. Iron(II)-folded single-chain nanoparticles: a metalloenzyme mimicking sustainable catalyst for highly enantioselective sulfa-Michael addition in water.
- Author
-
Wang, Weiying, Wang, Jiajun, Li, Shiye, Li, Chaoping, Tan, Rong, and Yin, Donghong
- Subjects
NANOPARTICLES ,IRON ,CHEMISTS ,WATER ,CATALYSIS ,HYDROPHOBIC interactions ,CATALYSTS - Abstract
Metalloenzyme is a source of inspiration for chemists who attempt to create versatile synthetic catalysts for aqueous catalysis. Herein, we impart metalloenzyme-like characteristics to a chiral Fe
II –oxazoline complex by incorporating an Fe(II) ion into a chiral oxazoline-containing discrete self-folded polymer, to realize highly enantioselective sulfa-Michael addition (SMA) in water. Intrachain FeII –oxazoline complexation together with hydrophobic interactions triggers the self-folding of the oxazoline-containing single polymeric chain in water. The formed FeII -folded single-chain polymeric nanoparticles (SCPNs) significantly accelerate the aqueous asymmetric SMA reaction via a self-folded hydrophobic compartment around the catalytic sites, reminiscent of metalloenzymatic catalysis. In addition, they can be facilely recovered for reuse by simple thermo-controlled separation due to their thermo-responsive properties. Such metallo-folded SCPNs combine the benefits of transition metal- and bio-catalyst, and avoid the tedious procedures of separation, which is a benefit for energy-saving and industrial applications. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
42. Biomass-derived metal–organic hybrids for CO2 transformation under ambient conditions.
- Author
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Wu, Yunyan, Zuo, Shouwei, Zhao, Yanfei, Wang, Huan, Li, Dongyang, Guo, Shien, Zhao, Zhijuan, Zhang, Jing, Han, Buxing, and Liu, Zhimin
- Subjects
CATALYSIS ,CATALYSTS ,PHYTIC acid - Abstract
The fabrication of catalysts that can activate CO
2 under ambient conditions is very interesting but challenging. Metal–organic hybrids (MOHs) have promising applications in catalysis, and their fabrication from renewable resources is very attractive. Herein, we report a simple protocol to fabricate metal–organic hybrids (MOHs) from chitosan, phytic acid and ZnCl2 , obtaining mesoporous MOH-Zn possessing –OH, –NH2 , and –PO4 groups. The resulting MOH-Zn shows excellent activity for CO2 activation and enables the cyclization of epoxides with CO2 to proceed under ambient conditions, affording a high turnover frequency of 7.8 h−1 . The high performance of MOH-Zn originates from the synergistic effects among multi-functional sites in the catalysts. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
43. Structural evolution of the Ru-bms complex to the real water oxidation catalyst of Ru-bda: the bite angle matters.
- Author
-
Yang, Jing, Liu, Bin, and Duan, Lele
- Subjects
OXIDATION of water ,CATALYSTS ,POLAR effects (Chemistry) ,RUTHENIUM catalysts ,CATALYSIS - Abstract
Ru-Based complexes have advanced the study of molecular water oxidation catalysts (WOCs) both in catalysis and mechanism. The electronic effect has always been considered as an essential factor for the catalyst properties while less attention has been focused on the bite angle effect on water oxidation catalysis. The Ru-bda ([Ru(bda)(pic)
2 ]; bda2− = 2,2′-bipyridine-6,6′-dicarboxylate; pic = 4-picoline) catalyst is one of the most active WOCs and it has a largely distorted octahedral configuration with an O–Ru–O bite angle of 123°. Herein, we replaced the carboxylate (–COO− ) groups of bda2− with two methylenesulfonate (–CH2 SO3 − ) groups and prepared a negatively charged ligand, bms2− (2,2′-bipyridine-6,6′-dimethanesulfonate), and the Ru-bms complex [Ru(bms)(pic)2 ]. The O–Ru–O bite angle changed from 123° in Ru-bda to 84° in Ru-bms, leading to a dramatic influence on the catalytic behavior. Systematic analysis of the reaction intermediates suggested that Ru-bms transformed all the way to Ru-bdavia oxidative decomposition under CeIV -driven water oxidation conditions. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
44. Synthesis of a high-performance low-platinum PtAg/C alloyed oxygen reduction catalyst through the gradual reduction method.
- Author
-
Zhao, Qing, Wang, Cheng, Wang, Haifeng, Wang, Jianlong, Tang, Yaping, Mao, Zongqiang, and Sasaki, Kazunari
- Subjects
PRECIOUS metals ,OXYGEN reduction ,CATALYSTS ,CATALYSIS ,PLATINUM electrodes ,SURFACE area ,DIFFUSION - Abstract
Herein, to reduce the platinum usage and increase the efficiency of noble metals in the catalysis of the oxygen reduction reaction, Ag was used as an assistant reductant, support and sacrificial template to prepare a low-platinum PtAg/C catalyst through a gradual reduction method with the final Pt mass percentage of 10.86 wt%. This as-synthesized low-platinum PtAg/C catalyst exhibited excellent oxygen reduction reaction activity and durability in an acid. With only 54.77% Pt usage, the half-wave potential of PtAg/C is 28 mV higher than that of commercial Pt/C and its limited diffusion current density is 1.1 times that of Pt/C. Furthermore, its electrochemically active surface area is 2.28 times higher than that of commercial Pt/C. Also, its area-specific activity and mass activity are approximately 1.85 and 4.22 times that of Pt/C, respectively. The PtAg/C catalyst displayed extraordinary ORR performance with higher limited current density and half-wave potential than commercial Pt/C after 10 000 potential cycles in HClO
4 . Thus, PtAg/C is more active and stable for ORR catalysis in acid. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
45. FeOCl/Ln (Ln = La or Y): efficient photo-Fenton catalysts for ibuprofen degradation.
- Author
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Shi, Xiaohua, Cui, Chao, Zhang, Lei, Zhang, Jian, and Liu, Guodong
- Subjects
ELECTRON pairs ,CATALYTIC activity ,CATALYSTS ,CATALYSIS ,RARE earth metals - Abstract
Rare earth element (La and Y) doped FeOCl has been successfully prepared, which shows efficient Fenton catalytic activity for ibuprofen degradation under simulated solar light. The degradation constants of FeOCl/La and FeOCl/Y in photo-Fenton catalysis are a factor of 7.12 and 5.21 times higher than that of FeOCl, respectively. According to DFT calculations, the doping of rare earth elements formed new catalytically active sites, which promoted the production of ˙OH radicals. The improved separation efficiency of photogenerated electron hole pairs in FeOCl/Ln (Ln = La or Y) also promotes the decomposition of H
2 O2 to produce ˙OH radicals. A synergistic mechanism for FeOCl/Ln (Ln = La or Y) is proposed for the enhanced catalytic performance. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
46. Engineering faster transglycosidases and their acceptor specificity.
- Author
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Tran, Linh T., Blay, Vincent, Luang, Sukanya, Eurtivong, Chatchakorn, Choknud, Sunaree, González-Díaz, Humbert, and Ketudat Cairns, James R.
- Subjects
ENZYMES ,CATALYSIS ,CATALYSTS ,QSAR models - Abstract
Transglycosidases are enzymes that have the potential to catalyze the synthesis of a wide range of high-value compounds starting from biomass-derived feedstocks. Improving their activity and broadening the substrate range are important goals to enable the widespread application of this family of biocatalysts. In this work, we engineered 20 mutants of the rice transglycosidase Os9BGlu31 and evaluated their catalysis in 462 reactions over 18 different substrates. This allowed us to identify mutants that expanded their substrate range and showed high activity, including W243L and W243N. We also developed double mutants that show very high activity on certain substrates and exceptional specificity towards hydrolysis, such as L241D/W243N. In order to guide a more general use of Os9BGlu31 variants as transglycosylation catalysts, we built cheminformatics models based on topological descriptors of the substrates. These models showed useful predictive potential on the external validation set and are allowing the identification of efficient catalytic routes to novel phytohormone and antibiotic glucoconjugates of interest. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
47. Highly enantioselective epoxidation of olefins by H2O2 catalyzed by a non-heme Fe(ii) catalyst of a chiral tetradentate ligand.
- Author
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Mitra, Mainak, Cusso, Olaf, Bhat, Satish S., Sun, Mingzhe, Cianfanelli, Marco, Costas, Miquel, and Nordlander, Ebbe
- Subjects
NITROALDOL reactions ,EPOXIDATION ,ALKENES ,CARBOXYLIC acids ,CATALYSIS ,CATALYSTS - Abstract
The chiral tetradentate N4-donor ligand, 1-methyl-2-({(S)-2-[(S)-1-(1-methylbenzimidazol-2-yl methyl)pyrrolidin-2-yl]pyrrolidin-1-yl}methyl) benzimidazole (S,S-
PDBz L), based on a chiral dipyrrolidine backbone, has been synthesized and its corresponding Fe(ii) complex has been prepared and characterized. The X-ray structure of the complex reveals that the Fe(ii) ion is in a distorted octahedral coordination environment with two cis-oriented coordination sites occupied by (labile) triflate anions. The ability of the iron complex to catalyze asymmetric epoxidation reactions of olefins with H2 O2 was investigated, using 2-cyclohexen-1-one, 2-cyclopenten-1-one, cis-β-methylstyrene, isophorone, chalcones and tetralones as substrates. Different carboxylic acids were used as additives to enhance yields and enantioselectivities, and 2-ethylhexanoic acid was found to give the best results. The catalysis results indicate that the Fe(ii) complex is capable of effecting comparatively high enantioselectivities (>80%) in the epoxidation reactions. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
48. Influence of nanoscale structuralisation on the catalytic performance of ZIF-8: a cautionary surface catalysis study.
- Author
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Linder-Patton, Oliver M., De Prinse, Thomas J., Furukawa, Shuhei, Bell, Stephen G., Sumida, Kenji, Doonan, Christian J., and Sumby, Christopher J.
- Subjects
METAL-organic frameworks ,CATALYSIS ,CRYSTAL morphology ,SCANNING electron microscopy ,NANOSTRUCTURED materials ,CATALYSTS - Abstract
Although metal–organic frameworks (MOFs) have been shown to catalyse a wide range of reactions, understanding the influence of nanoscale structuralisation (e.g. crystal size and morphology) on their performance is a difficult challenge. Here, we have prepared Zn(2-mIM)
2 (ZIF-8; 2-mIM− = 2-methylimidazolate) crystals of varied size and morphology, and studied the catalytic properties of these samples in the context of the transesterification of vinyl acetate with hexanol. ZIF-8 has previously been shown to catalyse reactions at Lewis acidic sites at the crystal surface and at defect sites. The substrates were selected as they are significantly larger than the pore apertures, allowing the reaction to be confined to the surface of the crystals and providing the best opportunity to understand the influence of the structuralisation on the observed properties. In this case, the rate of hexyl acetate production increased as the crystal size was reduced; however, the effect of crystal morphology on the rate of reaction was not appreciable due to the instability of ZIF-8 under catalytic conditions. It was clearly observed that the surface of ZIF-8 was unstable in catalytic conditions featuring hydrophobic reagents with a polar functional groups, with scanning electron microscopy (SEM) revealing indiscriminate etching of all crystal surfaces. Atomic adsorption spectrometry (AAS) analyses confirmed the etching led to significant leaching of Zn2+ , which was observed to contribute considerably to the catalytic activity of ZIF-8. Our results highlight the need for fundamental characterisation of MOF catalysts to enable their deployment under a wider variety of catalytic conditions. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
49. Amorphous saturated cerium–tungsten–titanium oxide nanofiber catalysts for NOx selective catalytic reaction.
- Author
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Dankeaw, Apiwat, Gualandris, Fabrizio, Silva, Rafael Hubert, Norrman, Kion, Gudik-Sørensen, Mads, Hansen, Kent Kammer, Ksapabutr, Bussarin, Esposito, Vincenzo, and Marani, Debora
- Subjects
TITANIUM oxides ,CATALYSTS ,CATALYSIS - Abstract
Herein for the first time, Ce
0.184 W0.07 Ti0.748 O2−δ nanofibers are prepared by electrospinning to serve as a catalyst in the selective catalytic reduction (SCR) process. The addition of cerium is proven to inhibit crystallization of TiO2 , yielding an amorphous TiOx -based solid solution stable up to 500 °C in air, with supersaturated substitutional Ce. At higher temperatures, anatase phase (titanium oxide) is then observed along with fluorite (cerium oxide). Tungsten is instead demonstrated to promote the reduction of the Ce4+ to Ce3+ with the formation of oxygen vacancies (δ). Catalytic experiments under the best working conditions (dry and in the absence of SO2 ) are performed to characterize the intrinsic catalytic behavior of the new catalysts. At a temperature lower than 300 °C, superior NOx conversion properties of the amorphous TiOx nanofibers over the crystallized TiO2 (anatase) nanofibers are observed and attributed to higher specific surface area (SSA), larger amount of oxygen vacancies, and higher amount of Ce3+ over Ce4+ . Comparison with literature data for ceria–tungsten-based nanoparticles also points out higher catalytic performances for the developed nanofibers at the lowest temperatures (<300 °C). This is mainly attributed to the unique nanofibrous morphology and to the doping approach. The stability of the amorphous Ce–W–TiOx nanofibers over time (120 h) and over a number of cycles (5) is demonstrated. Yet, superior catalytic performances of the developed catalysts in a wide range of temperatures (200–500 °C) over state-of-the-art material V–W–titania nanoparticles and nanofibers are also proven. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
50. Group 3 dialkyl complexes of a rigid monoanionic NNN-donor pincer ligand: synthesis, structures, unexpected reactivity with CPh3+, and hydroamination catalysis.
- Author
-
Vasanthakumar, Aathith, Gray, Novan A. G., Franko, Christopher J., Murphy, Maia C., and Emslie, David J. H.
- Subjects
ELECTRON paramagnetic resonance spectroscopy ,CATALYSIS ,ZWITTERIONS ,HYDROAMINATION ,ALKENES ,CATALYSTS ,OXIDATION - Abstract
Palladium-catalyzed coupling of 4,5-dibromo-2,7,9,9-tetramethylacridan with two equivalents of 1,3-diisopropylimidazolin-2-imine afforded 4,5-bis(1,3-diisopropylimidazolin-2-imino)-2,7,9,9-tetramethylacridan, H[AII
2 ]. Reaction of the H[AII2 ] pro-ligand with one equivalent of [M(CH2 SiMe3 )3 (THF)2 ] (M = Y or Sc) yielded the base-free neutral dialkyl complexes [(AII2 )M(CH2 SiMe3 )2 ] {M = Y (1) and Sc (2)}. The rigid AII2 pincer ligand affords a similar steric profile to the previously reported XA2 pincer ligand, but is monoanionic rather than dianionic. Reaction of 1 with one equiv. of [CPh3 ][B(C6 F5 )4 ] in C6 D5 Br generated a highly active catalyst for intramolecular alkene hydroamination. However, rather than forming the expected monoalkyl cation, this reaction afforded a diamagnetic product which was identified as [(AII2 -CH2 SiMe3 )Y(CH2 SiMe3 )2 ][B(C6 F5 )4 ] (3; AII2 -CH2 SiMe3 is a neutral tridentate ligand with a central amine donor flanked by imidazolin-2-imine groups) in approx. 20% yield, accompanied by HCPh3 (∼2 equiv. relative to 3), an unidentified paramagnetic product (detected by EPR spectroscopy), and a small amount of colourless precipitate. The unexpected reactivity of 1 with CPh3 + is thought to involve initial AII2 ligand backbone oxidation, given that the zwitterionic form of the ligand contains a phenylene ring with two adjacent anionic nitrogen donors, similar to a redox-non-innocent, dianionic ortho-phenylenediamido ligand. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
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