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2756 KiB

Open AccessFeature PaperCommunication

Halide-Enhanced Catalytic Activity of Palladium Nanoparticles Comes at the Expense of Catalyst Recovery

by Azzedine Bouleghlimat, Mazin A. Othman, Louis V. Lagrave, Soichiro Matsuzawa, Yoshinobu Nakamura, Syuji Fujii and Niklaas J. Buurma

Catalysts 2017, 7(9), 280; https://doi.org/10.3390/catal7090280 - 19 Sep 2017

Cited by 10 | Viewed by 5289

Abstract

In this communication, we present studies of the oxidative homocoupling of arylboronic acids catalyzed by immobilised palladium nanoparticles in aqueous solution. This reaction is of significant interest because it shares a key transmetallation step with the well-known Suzuki-Miyaura cross-coupling reaction. Additives can have [...] Read more.

In this communication, we present studies of the oxidative homocoupling of arylboronic acids catalyzed by immobilised palladium nanoparticles in aqueous solution. This reaction is of significant interest because it shares a key transmetallation step with the well-known Suzuki-Miyaura cross-coupling reaction. Additives can have significant effects on catalysis, both in terms of reaction mechanism and recovery of catalytic species, and our aim was to study the effect of added halides on catalytic efficiency and catalyst recovery. Using kinetic studies, we have shown that added halides (added as NaCl and NaBr) can increase the catalytic activity of the palladium nanoparticles more than 10-fold, allowing reactions to be completed in less than half a day at 30 °C. However, this increased activity comes at the expense of catalyst recovery. The results are in agreement with a reaction mechanism in which, under conditions involving high concentrations of chloride or bromide, palladium leaching plays an important role. Considering the evidence for analogous reactions occurring on the surface of palladium nanoparticles under different reaction conditions, we conclude that additives can exert a significant effect on the mechanism of reactions catalyzed by nanoparticles, including switching from a surface reaction to a solution reaction. The possibility of this switch in mechanism may also be the cause for the disagreement on this topic in the literature. Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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1135 KiB

Open AccessFeature PaperArticle

Catalytic Performance of Fe(II)-Scorpionate Complexes towards Cyclohexane Oxidation in Organic, Ionic Liquid and/or Supercritical CO₂ Media: A Comparative Study

by Ana P. C. Ribeiro, Luísa M. D. R. S. Martins, Elisabete C. B. A. Alegria, Inês A. S. Matias, Tiago A. G. Duarte and Armando J. L. Pombeiro

Catalysts 2017, 7(8), 230; https://doi.org/10.3390/catal7080230 - 02 Aug 2017

Cited by 18 | Viewed by 5103

Abstract

The catalytic activity of the iron(II) C-scorpionate complexes [FeCl₂{HC(pz)₃}] 1 (pz = pyrazol-1-yl) and [FeCl₂{HOCH₂C(pz)₃}] 2, and of their precursor FeCl₂·2H₂O 3, towards cyclohexane oxidation with tert [...] Read more.

The catalytic activity of the iron(II) C-scorpionate complexes [FeCl₂{HC(pz)₃}] 1 (pz = pyrazol-1-yl) and [FeCl₂{HOCH₂C(pz)₃}] 2, and of their precursor FeCl₂·2H₂O 3, towards cyclohexane oxidation with tert-butyl hydroperoxide was evaluated and compared in different media: acetonitrile, ionic liquids (1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF₆], and 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, [bmim][FAP]), supercritical carbon dioxide (scCO₂), and scCO₂/[bmim][X] (X = PF₆ or FAP) mixtures. The use of such alternative solvents led to efficient and selective protocols for the oxidation of cyclohexane. Moreover, tuning the alcohol/ketone selectivity was possible by choosing the suitable solvent. Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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2161 KiB

Open AccessFeature PaperArticle

Solventless Coupling of Epoxides and CO₂ in Compressed Medium Catalysed by Fluorinated Metalloporphyrins

by Rui M. B. Carrilho, Lucas D. Dias, Raquel Rivas, Mariette M. Pereira, Carmen Claver and Anna M. Masdeu-Bultó

Catalysts 2017, 7(7), 210; https://doi.org/10.3390/catal7070210 - 14 Jul 2017

Cited by 17 | Viewed by 5120

Abstract

Metal complexes of meso-arylporphyrins (Cr(III), Fe(III), and Zn(II)) were evaluated in the coupling reaction of cyclohexene oxide (CHO) with CO₂ in compressed medium, where the Cr complexes were demonstrated to be the most active systems, leading predominantly to copolymerisation products. It [...] Read more.

Metal complexes of meso-arylporphyrins (Cr(III), Fe(III), and Zn(II)) were evaluated in the coupling reaction of cyclohexene oxide (CHO) with CO₂ in compressed medium, where the Cr complexes were demonstrated to be the most active systems, leading predominantly to copolymerisation products. It is noteworthy that no addition of solvent was required. To improve the catalytic activity, and to simultaneously increase the solubility in compressed CO₂, a new fluorinated catalyst, tetrakis(4-trifluoromethylphenyl)porphyrinatochromium(III) chloride (CrCl-pCF₃TPP), was applied to this reaction. The alternating copolymerisation of CHO with CO₂, using the Cr(III) fluorinated porphyrin catalyst, required the use of a co-catalyst, bis(triphenylphosphine)iminium chloride (PPNCl), with the best yields of copolymers being obtained at 80 °C, and CO₂ pressures in the range of 50–110 bar, over a period of 24 h, with a low catalyst/substrate molar ratio (0.07%). The polycarbonate’s structure was analysed by ¹H NMR, ¹³C NMR, and MALDI-TOF spectroscopy, which demonstrated high carbonate incorporations (98–99%). Gel permeation chromatography revealed number-average molecular weights (M_n) in the range of 4800–12,800 and narrow molecular weight distributions (M_w/M_n ≤ 1.63). Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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14348 KiB

Open AccessArticle

A Reusable Palladium/Cationic 2,2′-Bipyridyl System-Catalyzed Double Mizoroki-Heck Reaction in Water

by Yu-Chi Chen, Chien-Chi Wu, Wei-Ting Liao, Ling-Jun Liu and Fu-Yu Tsai

Catalysts 2017, 7(6), 177; https://doi.org/10.3390/catal7060177 - 02 Jun 2017

Cited by 5 | Viewed by 3530

Abstract

A reusable PdCl₂(NH₃)₂/cationic 2,2′-bipyridyl system was used to catalyze the double Mizoroki-Heck reaction of aryl iodides with electron-deficient alkenes in water in the absence of inert gas, giving β,β-diarylated carbonyl derivatives in good to excellent yields. The [...] Read more.

A reusable PdCl₂(NH₃)₂/cationic 2,2′-bipyridyl system was used to catalyze the double Mizoroki-Heck reaction of aryl iodides with electron-deficient alkenes in water in the absence of inert gas, giving β,β-diarylated carbonyl derivatives in good to excellent yields. The formation of unsymmetrical β,β-diarylated alkenes were also studied by coupling aryl iodides with the corresponding aryl-substituted α,β-unsaturated carbonyl compounds. This water-soluble catalyst can be swiftly separated from the organic layer using simple extraction for the further reuse, and, thus, makes it an operationally-simple and environmentally-benign procedure. Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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4137 KiB

Open AccessArticle

Are Directed Evolution Approaches Efficient in Exploring Nature’s Potential to Stabilize a Lipase in Organic Cosolvents?

by Ulrich Markel, Leilei Zhu, Victorine Josiane Frauenkron-Machedjou, Jing Zhao, Marco Bocola, Mehdi D. Davari, Karl-Erich Jaeger and Ulrich Schwaneberg

Catalysts 2017, 7(5), 142; https://doi.org/10.3390/catal7050142 - 07 May 2017

Cited by 34 | Viewed by 6777

Abstract

Despite the significant advances in the field of protein engineering, general design principles to improve organic cosolvent resistance of enzymes still remain undiscovered. Previous studies drew conclusions to engineer enzymes for their use in water-miscible organic solvents based on few amino acid substitutions. [...] Read more.

Despite the significant advances in the field of protein engineering, general design principles to improve organic cosolvent resistance of enzymes still remain undiscovered. Previous studies drew conclusions to engineer enzymes for their use in water-miscible organic solvents based on few amino acid substitutions. In this study, we conduct a comparison of a Bacillus subtilis lipase A (BSLA) library—covering the full natural diversity of single amino acid substitutions at all 181 positions of BSLA—with three state of the art random mutagenesis methods: error-prone PCR (epPCR) with low and high mutagenesis frequency (epPCR-low and high) as well as a transversion-enriched Sequence Saturation Mutagenesis (SeSaM-Tv P/P) method. Libraries were searched for amino acid substitutions that increase the enzyme’s resistance to the water-miscible organic cosolvents 1,4-dioxane (DOX), 2,2,2-trifluoroethanol (TFE), and dimethyl sulfoxide (DMSO). Our analysis revealed that 5%–11% of all possible single substitutions (BSLA site-saturation mutagenesis (SSM) library) contribute to improved cosolvent resistance. However, only a fraction of these substitutions (7%–12%) could be detected in the three random mutagenesis libraries. To our knowledge, this is the first study that quantifies the capability of these diversity generation methods generally employed in directed evolution campaigns and compares them to the entire natural diversity with a single substitution. Additionally, the investigation of the BSLA SSM library revealed only few common beneficial substitutions for all three cosolvents as well as the importance of introducing surface charges for organic cosolvent resistance—most likely due to a stronger attraction of water molecules. Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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2372 KiB

Open AccessArticle

Efficient Hydrolysis of Lignocellulose by Acidic Ionic Liquids under Low-Toxic Condition to Microorganisms

by Kosuke Kuroda, Ken Inoue, Kyohei Miyamura, Heri Satria, Kenji Takada, Kazuaki Ninomiya and Kenji Takahashi

Catalysts 2017, 7(4), 108; https://doi.org/10.3390/catal7040108 - 07 Apr 2017

Cited by 4 | Viewed by 4314

Abstract

Lignocellulose is known as a renewable resource, and acidic ionic liquids have been highlighted as efficient catalysts for hydrolysis of cellulose. To achieve successive hydrolysis and fermentation, efficient hydrolysis with sufficiently diluted acidic ionic liquids is necessary because acidic ionic liquids are toxic [...] Read more.

Lignocellulose is known as a renewable resource, and acidic ionic liquids have been highlighted as efficient catalysts for hydrolysis of cellulose. To achieve successive hydrolysis and fermentation, efficient hydrolysis with sufficiently diluted acidic ionic liquids is necessary because acidic ionic liquids are toxic to fermentative microorganisms. Escherichia coli was confirmed to grow in 0.05 M dilute acidic ionic liquid—1-(1-butylsulfonic)-3-methylimidazolium hydrogen sulfate ([Sbmim][HSO₄])—although the growth was suppressed in more concentrated solutions. Therefore, we applied the 0.05 M [Sbmim][HSO₄] solution to hydrolysis of bagasse, leading to a glucose yield of 48% at 190 °C. This value is greater than that obtained with a concentrated [Sbmim][HSO₄] solution, which is not suitable for the growth of Escherichia coli (yield: 40% in a 1.0 M solution). Efficient hydrolysis with acidic ionic liquids under low-toxic condition was achieved. Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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Review

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2655 KiB

Open AccessFeature PaperReview

Catalytic Conversion of Carbohydrates to Furanic Derivatives in the Presence of Choline Chloride

by François Jérôme and Karine De Oliveira Vigier

Catalysts 2017, 7(7), 218; https://doi.org/10.3390/catal7070218 - 20 Jul 2017

Cited by 18 | Viewed by 6101

Abstract

The synthesis of furanic derivatives (5-hydroxymethylfurfural (HMF), furfural…) from carbohydrates is of high interest for a wide range of applications. These reactions are carried out in the presence of various solvents, and among them choline chloride can be used. It is a salt [...] Read more.

The synthesis of furanic derivatives (5-hydroxymethylfurfural (HMF), furfural…) from carbohydrates is of high interest for a wide range of applications. These reactions are carried out in the presence of various solvents, and among them choline chloride can be used. It is a salt that can form a low melting mixture with a carbohydrate (fructose, glucose…) or a deep eutectic mixture with carboxylic acid. A review of the studies performed in the conversion of carbohydrates to furanic derivatives in the presence of choline chloride is presented here with the advantages and drawbacks of this solvent. Choline chloride can enhance the selectivity to HMF by stabilizing effect and allows the conversion of highly concentrated feed. However, the extraction of the products from these solvents still needs improvement. Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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5038 KiB

Open AccessFeature PaperReview

Bimetallic Nanoparticles in Alternative Solvents for Catalytic Purposes

by Trung Dang-Bao, Daniel Pla, Isabelle Favier and Montserrat Gómez

Catalysts 2017, 7(7), 207; https://doi.org/10.3390/catal7070207 - 07 Jul 2017

Cited by 50 | Viewed by 9158

Abstract

Bimetallic nanoparticles represent attractive catalytic systems thanks to the synergy between both partners at the atomic level, mainly induced by electronic effects which in turn are associated with the corresponding structures (alloy, core-shell, hetero-dimer). This type of engineered material can trigger changes in [...] Read more.

Bimetallic nanoparticles represent attractive catalytic systems thanks to the synergy between both partners at the atomic level, mainly induced by electronic effects which in turn are associated with the corresponding structures (alloy, core-shell, hetero-dimer). This type of engineered material can trigger changes in the kinetics of catalyzed processes by variations on the electrophilicity/nucleophilicity of the metal centers involved and also promote cooperative effects to foster organic transformations, including multi-component and multi-step processes. Solvents become a crucial factor in the conception of catalytic processes, not only due to their environmental impact, but also because they can preserve the bimetallic structure during the catalytic reaction and therefore increase the catalyst life-time. In this frame, the present review focuses on the recent works described in the literature concerning the synthesis of bimetallic nanoparticles in non-conventional solvents, i.e., other than common volatile compounds, for catalytic applications. Full article

(This article belongs to the Special Issue Catalysis in Innovative Solvents)

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