Catalysts

24563 KiB

Open AccessFeature PaperReview

What Can We Learn in Electrocatalysis, from Nanoparticulated Precious and/or Non-Precious Catalytic Centers Interacting with Their Support?

by Juan Manuel Mora-Hernández, Yun Luo and Nicolas Alonso-Vante

Catalysts 2016, 6(9), 145; https://doi.org/10.3390/catal6090145 - 21 Sep 2016

Cited by 17 | Viewed by 8997

Abstract

This review is devoted to discussing the state of the art in the relevant aspects of the synthesis of novel precious and non-precious electrocatalysts. It covers the production of Pt- and Pd-based electrocatalysts synthesized by the carbonyl chemical route, the synthesis description for [...] Read more.

This review is devoted to discussing the state of the art in the relevant aspects of the synthesis of novel precious and non-precious electrocatalysts. It covers the production of Pt- and Pd-based electrocatalysts synthesized by the carbonyl chemical route, the synthesis description for the preparation of the most catalytically active transition metal chalcogenides, then the employment of free-surfactants synthesis routes to produce non-precious electrocatalysts. A compilation of the best precious electrocatalysts to perform the hydrogen oxidation reaction (HOR) is described; a section is devoted to the synthesis and electrocatalytic evaluation of non-precious materials which can be used to perform the HOR in alkaline medium. Apropos the oxygen reduction reaction (ORR), the synthesis and modification of the supports is also discussed as well, aiming at describing the state of the art to improve kinetics of low temperature fuel cell reactions via the hybridization process of the catalytic center with a variety of carbon-based, and ceramic-carbon supports. Last, but not least, the review covers the experimental half-cells results in a micro-fuel cell platform obtained in our laboratory, and by other workers, analyzing the history of the first micro-fuel cell systems and their tailoring throughout the time bestowing to the design and operating conditions. Full article

(This article belongs to the Special Issue Catalysis for Low Temperature Fuel Cells)

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1363 KiB

Open AccessArticle

Synthesis, Characterization, and Catalytic Hydrogenation Activity of New N-Acyl-Benzotriazole Rh(I) and Ru(III) Complexes in [bmim][BF₄]

by Hakan Ünver and Filiz Yılmaz

Catalysts 2016, 6(9), 147; https://doi.org/10.3390/catal6090147 - 20 Sep 2016

Cited by 10 | Viewed by 4999

Abstract

The hydrogenation activity of new N-acyl-benzotriazole Rh(I) and Ru(III) complexes in ionic liquid media is reported in this study. Both complexes were completely soluble in 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF₄], and they were able to catalyze the hydrogenation of styrene and 1-octene. [...] Read more.

The hydrogenation activity of new N-acyl-benzotriazole Rh(I) and Ru(III) complexes in ionic liquid media is reported in this study. Both complexes were completely soluble in 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF₄], and they were able to catalyze the hydrogenation of styrene and 1-octene. While ethylbenzene conversion in styrene hydrogenation reached 84% when the Ru complex was used, 100% conversion was obtained with the Rh complex at 393 K in 6 h. Additionally, total conversion in 1-octene hydrogenation reached 100% with the Rh complex in [bmim][BF₄] media. The hydrogenation of styrene and 1-octene in dimethyl sulfoxide (DMSO) and toluene was also studied to compare the solvent effect on catalytic system. The effect of some catalytic parameters such as temperature, H₂ (g) pressure, and catalyst amount on the conversion was examined, and it was found that the conversion increased parallel to the increasing temperature and H₂ pressure. The recyclability of catalysts was also investigated, and it was revealed that the Rh complex in particular maintained the activity for at least 10 cycles. Full article

(This article belongs to the Special Issue Organometallic Catalysis for Organic Synthesis)

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12932 KiB

Open AccessArticle

Preparation of Fe₃O₄/TiO₂/C Nanocomposites and Their Application in Fenton-Like Catalysis for Dye Decoloration

by Xiaoyang Liu, Qian Zhang, Baowei Yu, Ruihan Wu, Jinxia Mai, Ruijue Wang, Lingyun Chen and Sheng-Tao Yang

Catalysts 2016, 6(9), 146; https://doi.org/10.3390/catal6090146 - 20 Sep 2016

Cited by 29 | Viewed by 5427

Abstract

Fe²⁺-H₂O₂ Fenton system is widely applied in water treatment nowadays, but the acidification and sludge generation are crucial problems to be solved. Herein, we report that Fe₃O₄/TiO₂/C nanocomposites (FTCNCs) were able to [...] Read more.

Fe²⁺-H₂O₂ Fenton system is widely applied in water treatment nowadays, but the acidification and sludge generation are crucial problems to be solved. Herein, we report that Fe₃O₄/TiO₂/C nanocomposites (FTCNCs) were able to catalyze the decomposition of H₂O₂ at neutral pH and can be applied in dye decoloration. FTCNCs were prepared by precipitating TiO₂ on Fe₃O₄ cores via the hydrolysis of tetrabutyl titanate followed by the hydrothermal dehydrogenization of glucose to deposit carbon on Fe₃O₄/TiO₂. The decoloration of methylene blue (MB) in the FTCNC-H₂O₂ Fenton-like system was monitored to reflect the catalytic activity of FTCNC. The radical generation capability was analyzed by electron spin resonance. Our results indicated that FTCNC-H₂O₂ Fenton-like system was efficient in decolorizing MB, and the radicals led to the near complete oxidation of MB. The FTCNC-H₂O₂ Fenton-like system could be used in a wide pH range of 4–9. A greater catalyst amount, a higher H₂O₂ concentration, and a higher temperature accelerated the decoloration kinetics. FTCNCs showed good activity after the regeneration of 8 cycles. The implication to the practical applications of FTCNCs in water treatment is discussed. Full article

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7284 KiB

Open AccessArticle

Facile Synthesis of Bimetallic Pt-Ag/Graphene Composite and Its Electro-Photo-Synergistic Catalytic Properties for Methanol Oxidation

by Shuhong Xu, Lingting Ye, Zhongshui Li, Yanli Wang, Fengling Lei and Shen Lin

Catalysts 2016, 6(9), 144; https://doi.org/10.3390/catal6090144 - 16 Sep 2016

Cited by 11 | Viewed by 6872

Abstract

A Pt-Ag/graphene composite (Pt-Ag/GNs) was synthesized by the facile aqueous solution method, in which Ag⁺ was first transformed into Ag₂O under UV light irradiation, and then Ag₂O, Pt²⁺, and graphene oxide (GO) were simultaneously reduced by [...] Read more.

A Pt-Ag/graphene composite (Pt-Ag/GNs) was synthesized by the facile aqueous solution method, in which Ag⁺ was first transformed into Ag₂O under UV light irradiation, and then Ag₂O, Pt²⁺, and graphene oxide (GO) were simultaneously reduced by formic acid. It was found that Pt-Ag bimetallic nanoparticles were highly dispersed on the surface of graphene, and their size distribution was narrow with an average diameter of 3.3 nm. Electrocatalytic properties of the Pt-Ag/GNs composite were investigated by cyclic voltammograms (CVs), chronoamperometry (CA), CO-stripping voltammograms, and electrochemical impedance spectrum (EIS) techniques. It was shown that the Pt-Ag/GNs composite has much higher catalytic activity and stability for the methanol oxidation reaction (MOR) and better tolerance toward CO poisoning when compared with Pt/GNs and the commercially available Johnson Matthey 20% Pt/C catalyst (Pt/C-JM). Furthermore, the Pt-Ag/GNs composite showed efficient electro-photo-synergistic catalysis for MOR under UV or visible light irradiation. Particularly in the presence of UV irradiation, the Pt-Ag/GNs composite exhibited an ultrahigh mass activity of 1842.4 mA·mg⁻¹, nearly 2.0 times higher than that without light irradiation (838.3 mA·mg⁻¹). Full article

(This article belongs to the Special Issue Catalysis for Low Temperature Fuel Cells)

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2863 KiB

Open AccessArticle

Catalytic Upgrading of Biomass-Derived Furfuryl Alcohol to Butyl Levulinate Biofuel over Common Metal Salts

by Lincai Peng, Ruili Tao and Yu Wu

Catalysts 2016, 6(9), 143; https://doi.org/10.3390/catal6090143 - 15 Sep 2016

Cited by 21 | Viewed by 5855

Abstract

Levulinate ester has been identified as a promising renewable fuel additive and platform chemical. Here, the use of a wide range of common metal salts as acid catalysts for catalytic upgrading of biomass-derived furfuryl alcohol to butyl levulinate was explored by conventional heating. [...] Read more.

Levulinate ester has been identified as a promising renewable fuel additive and platform chemical. Here, the use of a wide range of common metal salts as acid catalysts for catalytic upgrading of biomass-derived furfuryl alcohol to butyl levulinate was explored by conventional heating. Both alkali and alkaline earth metal chlorides did not lead effectively to the conversion of furfuryl alcohol, while several transition metal chlorides (CrCl₃, FeCl₃, and CuCl₂) and AlCl₃ exhibited catalytic activity for the synthesis of butyl levulinate. For their sulfates (Cr(III), Fe(III), Cu(II), and Al(III)), the catalytic activity was low. The reaction performance was correlated with the Brønsted acidity of the reaction system derived from the hydrolysis/alcoholysis of cations, but was more dependent on the Lewis acidity from the metal salts. Among these investigated metal salts, CuCl₂ was found to be uniquely effective, leading to the conversion of furfuryl alcohol to butyl levulinate with an optimized yield of 95%. Moreover, CuCl₂ could be recovered efficiently from the resulting reaction mixture and remained with almost unchanged catalytic activity in multiple recycling runs. Full article

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3684 KiB

Open AccessFeature PaperArticle

Solventless Synthesis of Quaterphenyls and Terphenyls from Chalcones and Allylsulfones under Phase Transfer Catalysis Conditions

by Domenico C. M. Albanese, Selene Brunialti and Dario Destro

Catalysts 2016, 6(9), 142; https://doi.org/10.3390/catal6090142 - 13 Sep 2016

Cited by 6 | Viewed by 5325

Abstract

Easily available chalcones and allyl sulfones along with cheap solid NaOH and polyethyleneglycol (PEG) 1000 have been used to directly generate the meta-terphenyl or quaterphenyl motifs under Phase Transfer Catalysis solventless conditions. The new approach provides an economic and environmentally friendly solution [...] Read more.

Easily available chalcones and allyl sulfones along with cheap solid NaOH and polyethyleneglycol (PEG) 1000 have been used to directly generate the meta-terphenyl or quaterphenyl motifs under Phase Transfer Catalysis solventless conditions. The new approach provides an economic and environmentally friendly solution to removal of hazardous bases as well as organic solvents. Full article

(This article belongs to the Special Issue Phase-Transfer Catalysts)

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2110 KiB

Open AccessCommunication

Olefin Hydroborations with Diamidocarbene–BH₃ Adducts at Room Temperature

by Dominika N. Lastovickova and Christopher W. Bielawski

Catalysts 2016, 6(9), 141; https://doi.org/10.3390/catal6090141 - 12 Sep 2016

Cited by 2 | Viewed by 4475

Abstract

An isolable N,N’-diamidocarbene (DAC) was previously shown to promote the B–H bond activation of various BH₃ complexes. The resultant DAC–BH₃ adducts facilitated olefin hydroborations under mild conditions and in the absence of exogenous initiators. The substrate scope for such transformations [...] Read more.

An isolable N,N’-diamidocarbene (DAC) was previously shown to promote the B–H bond activation of various BH₃ complexes. The resultant DAC–BH₃ adducts facilitated olefin hydroborations under mild conditions and in the absence of exogenous initiators. The substrate scope for such transformations was further explored and is described herein. While organoboranes were obtained in quantitative yields from various terminal and internal olefins, use of the latter substrates resulted in intramolecular ring-expansion of the newly formed DAC–borane adducts. Full article

(This article belongs to the Special Issue Tailor-Made NHC Ligands)

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1470 KiB

Open AccessFeature PaperArticle

Highly Efficient Tetranuclear Zn^II₂Ln^III₂ Catalysts for the Friedel–Crafts Alkylation of Indoles and Nitrostyrenes

by Prashant Kumar, Smaragda Lymperopoulou, Kieran Griffiths, Stavroula I. Sampani and George E. Kostakis

Catalysts 2016, 6(9), 140; https://doi.org/10.3390/catal6090140 - 12 Sep 2016

Cited by 16 | Viewed by 7325

Abstract

We demonstrate for the first time the high efficacy of tetranuclear Zn^II₂Ln^III₂ coordination clusters (CCs) as catalysts for the Friedel–Crafts (FC) alkylation of indoles with a range of trans-β-nitrostyrenes. The reaction proceeds in good to excellent yields [...] Read more.

We demonstrate for the first time the high efficacy of tetranuclear Zn^II₂Ln^III₂ coordination clusters (CCs) as catalysts for the Friedel–Crafts (FC) alkylation of indoles with a range of trans-β-nitrostyrenes. The reaction proceeds in good to excellent yields (76%–99%) at room temperature with catalyst loadings as low as 1.0 mol %. Full article

(This article belongs to the Special Issue Organometallic Catalysis for Organic Synthesis)

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2836 KiB

Open AccessArticle

Effect of an Sb-Doped SnO₂ Support on the CO-Tolerance of Pt₂Ru₃ Nanocatalysts for Residential Fuel Cells

by Yoshiyuki Ogihara, Hiroshi Yano, Masahiro Watanabe, Akihiro Iiyama and Hiroyuki Uchida

Catalysts 2016, 6(9), 139; https://doi.org/10.3390/catal6090139 - 10 Sep 2016

Cited by 7 | Viewed by 5727

Abstract

We prepared monodisperse Pt₂Ru₃ nanoparticles supported on carbon black and Sb-doped SnO₂ (denoted as Pt₂Ru₃/CB and Pt₂Ru₃/Sb-SnO₂) with identical alloy composition and particle size distribution by the nanocapsule method. [...] Read more.

We prepared monodisperse Pt₂Ru₃ nanoparticles supported on carbon black and Sb-doped SnO₂ (denoted as Pt₂Ru₃/CB and Pt₂Ru₃/Sb-SnO₂) with identical alloy composition and particle size distribution by the nanocapsule method. The activities for the hydrogen oxidation reaction (HOR) of these anode catalysts were examined in H₂-saturated 0.1 M HClO₄ solution in both the presence and absence of carbon monoxide by use of a channel flow electrode at 70 °C. It was found that the CO-tolerant HOR mass activity at 0.02 V versus a reversible hydrogen electrode (RHE) on the Pt₂Ru₃/Sb-SnO₂ electrode was higher than that at the Pt₂Ru₃/CB electrode in 0.1 M HClO₄ solution saturated with 1000 ppm CO (H₂-balance). The CO tolerance mechanism of these catalysts was investigated by in situ attenuated total reflection Fourier transform infrared reflection-adsorption spectroscopy (ATR-FTIRAS) in 1% CO/H₂-saturated 0.1 M HClO₄ solution at 60 °C. It was found, for the Pt₂Ru₃/Sb-SnO₂ catalyst, that the band intensity of CO linearly adsorbed (CO_L) at step/edge sites was suppressed, together with a blueshift of the CO_L peak at terrace sites. On this surface, the HOR active sites were concluded to be more available than those on the CB-supported catalyst surface. The observed changes in the adsorption states of CO can be ascribed to an electronic modification effect by the Sb-SnO₂ support. Full article

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1932 KiB

Open AccessReview

TiO₂ Solar Photocatalytic Reactor Systems: Selection of Reactor Design for Scale-up and Commercialization—Analytical Review

by Yasmine Abdel-Maksoud, Emad Imam and Adham Ramadan

Catalysts 2016, 6(9), 138; https://doi.org/10.3390/catal6090138 - 10 Sep 2016

Cited by 103 | Viewed by 16363

Abstract

For the last four decades, viability of photocatalytic degradation of organic compounds in water streams has been demonstrated. Different configurations for solar TiO₂ photocatalytic reactors have been used, however pilot and demonstration plants are still countable. Degradation efficiency reported as a function [...] Read more.

For the last four decades, viability of photocatalytic degradation of organic compounds in water streams has been demonstrated. Different configurations for solar TiO₂ photocatalytic reactors have been used, however pilot and demonstration plants are still countable. Degradation efficiency reported as a function of treatment time does not answer the question: which of these reactor configurations is the most suitable for photocatalytic process and optimum for scale-up and commercialization? Degradation efficiency expressed as a function of the reactor throughput and ease of catalyst removal from treated effluent are used for comparing performance of different reactor configurations to select the optimum for scale-up. Comparison included parabolic trough, flat plate, double skin sheet, shallow ponds, shallow tanks, thin-film fixed-bed, thin film cascade, step, compound parabolic concentrators, fountain, slurry bubble column, pebble bed and packed bed reactors. Degradation efficiency as a function of system throughput is a powerful indicator for comparing the performance of photocatalytic reactors of different types and geometries, at different development scales. Shallow ponds, shallow tanks and fountain reactors have the potential of meeting all the process requirements and a relatively high throughput are suitable for developing into continuous industrial-scale treatment units given that an efficient immobilized or supported photocatalyst is used. Full article

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3400 KiB

Open AccessArticle

Time- and Temperature-Varying Activation Energies: Isobutane Selective Oxidation to Methacrolein over Phosphomolybdic Acid and Copper(II) Phosphomolybdates

by Trevor C. Brown, David J. Miron, Susannah L. Brown and Shane M. Kendell

Catalysts 2016, 6(9), 137; https://doi.org/10.3390/catal6090137 - 10 Sep 2016

Cited by 2 | Viewed by 5019

Abstract

The selective oxidation energetics of isobutane to methacrolein over phosphomolybdic acid and copper(II) phosphomolybdates have been investigated using low-pressure, pseudo-steady-state and temperature-programming techniques. Time-varying flexible least squares methods were used to determine variations in oxidation activation energies as the temperature increases at 5 [...] Read more.

The selective oxidation energetics of isobutane to methacrolein over phosphomolybdic acid and copper(II) phosphomolybdates have been investigated using low-pressure, pseudo-steady-state and temperature-programming techniques. Time-varying flexible least squares methods were used to determine variations in oxidation activation energies as the temperature increases at 5 °C·min⁻¹. Catalyst activity stabilizes by the fourth consecutive temperature-programmed run. Rate parameters increase linearly with temperature in two sinusoidal, oscillating wave packets. For H₃PMo₁₂O₄₀, three distinct reaction pathways are apparent in the fourth run with activation energies 76 ± 3, 93 ± 7 and 130 ± 3 kJ·mol⁻¹, and under these experimental conditions are observed at the optimum temperatures 704 ± 7 K, 667 ± 25 K and 745 ± 7 K, respectively. Over the copper-containing catalysts, two pathways are apparent: 76 ± 3 kJ·mol⁻¹ at 665 ± 9 K and 130 ± 3 kJ·mol⁻¹ at 706 ± 9 K. The three activation energies indicate either different reaction pathways leading to methacrolein or distinct active sites on the catalyst surface. The intermediate activation energy, 93 kJ·mol⁻¹, only observed over phosphomolybdic acid, may be linked to hydrogen bonding. Differences in optimum temperatures for the same activation energies for H₃PMO₁₂O₄₀ and for the copper catalysts indicate that compensating entropy changes are smaller over H₃PMo₁₂O₄₀. The inclusion of copper enhances catalyst stability and activity. Full article

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4349 KiB

Open AccessArticle

WS₂ as an Effective Noble-Metal Free Cocatalyst Modified TiSi₂ for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation

by Dongmei Chu, Chunyong Zhang, Ping Yang, Yukou Du and Cheng Lu

Catalysts 2016, 6(9), 136; https://doi.org/10.3390/catal6090136 - 10 Sep 2016

Cited by 23 | Viewed by 7802

Abstract

A noble-metal free photocatalyst consisting of WS₂ and TiSi₂ being used for hydrogen evolution under visible light irradiation, has been successfully prepared by in-situ formation of WS₂ on the surface of TiSi₂ in a thermal reaction. The obtained samples [...] Read more.

A noble-metal free photocatalyst consisting of WS₂ and TiSi₂ being used for hydrogen evolution under visible light irradiation, has been successfully prepared by in-situ formation of WS₂ on the surface of TiSi₂ in a thermal reaction. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results demonstrate that WS₂ moiety has been successfully deposited on the surface of TiSi₂ and some kind of chemical bonds, such as Ti-S-W and Si-S-W, might have formed on the interface of the TiSi₂ and WS₂ components. Optical and photoelectrochemical investigations reveal that WS₂/TiSi₂ composite possesses lower hydrogen evolution potential and enhanced photogenerated charge separation and transfer efficiency. Under 6 h of visible light (λ > 420 nm) irradiation, the total amount of hydrogen evolved from the optimal WS₂/TiSi₂ catalyst is 596.4 μmol·g⁻¹, which is around 1.5 times higher than that of pure TiSi₂ under the same reaction conditions. This study shows a paradigm of developing the effective, scalable and inexpensive system for photocatalytic hydrogen generation. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis & Hydrogen Storage)

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8824 KiB

Open AccessArticle

Noble Metal-Free Ceria-Zirconia Solid Solutions Templated by Tobacco Materials for Catalytic Oxidation of CO

by Donglai Zhu, Deliang Duan, Yi Han, Jiao He, Yi He, Yongjuan Chen, Wei Zhang, Zhiyin Yan, Jiaqiang Wang and Fagui Yuan

Catalysts 2016, 6(9), 135; https://doi.org/10.3390/catal6090135 - 9 Sep 2016

Cited by 9 | Viewed by 5530

Abstract

A series of ceria-zirconia solid solutions were synthesized using tobacco leaves, stems and stem-silks as biotemplates. A combination of physicochemical techniques such as powder X-ray diffraction (XRD), N₂ adsorption/desorption measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to [...] Read more.

A series of ceria-zirconia solid solutions were synthesized using tobacco leaves, stems and stem-silks as biotemplates. A combination of physicochemical techniques such as powder X-ray diffraction (XRD), N₂ adsorption/desorption measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the as-synthesized samples. The results show that the morphologies of the templates were well replicated in the obtained ceria-zirconia solid solutions. Catalytic oxidation activities of CO over the ceria-zirconia solid solutions were then investigated. The catalyst templated by tobacco stem-silk exhibited higher conversion of CO at lower temperature than that of ceria-zirconia solid solutions templated by tobacco leaves and stems or without templates due to its special morphology. The catalyst even showed similar CO conversion when compared to ceria-zirconia solid solutions doped with 1.0 wt % noble metals such as Pt, Ag and Au. The results highlighted the advantages of using tobacco as biotemplate. Full article

(This article belongs to the Special Issue Ceria-based Catalysts)

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2934 KiB

Open AccessArticle

Efficient Hydrogenolysis of Guaiacol over Highly Dispersed Ni/MCM-41 Catalyst Combined with HZSM-5

by Songbai Qiu, Ying Xu, Yujing Weng, Longlong Ma and Tiejun Wang

Catalysts 2016, 6(9), 134; https://doi.org/10.3390/catal6090134 - 8 Sep 2016

Cited by 43 | Viewed by 5881

Abstract

A series of MCM-41 supported Ni catalysts with high metal dispersion was successfully synthesized by simple co-impregnation using proper ethylene glycol (EG). The acquired Ni-based catalysts performed the outstanding hydrogenolysis activity of guaiacol. The effects of the synthesis parameters including drying temperature, calcination [...] Read more.

A series of MCM-41 supported Ni catalysts with high metal dispersion was successfully synthesized by simple co-impregnation using proper ethylene glycol (EG). The acquired Ni-based catalysts performed the outstanding hydrogenolysis activity of guaiacol. The effects of the synthesis parameters including drying temperature, calcination temperature, and metal loading on the physical properties of NiO nanoparticles were investigated through the use of X-ray diffraction (XRD). The drying temperature was found to significantly influence the particle sizes of NiO supported on MCM-41, but the calcination temperature and metal loading had less influence. Interestingly, the small particle size (≤3.3 nm) and the high dispersion of NiO particles were also obtained for co-impregnation on the mixed support (MCM-41:HZSM-5 = 1:1), similar to that on the single MCM-41 support, leading to excellent hydrogenation activity at low temperature. The guaiacol conversion could reach 97.9% at 150 °C, and the catalytic activity was comparative with that of noble metal catalysts. The hydrodeoxygenation (HDO) performance was also promoted by the introduction of acidic HZSM-5 zeolite and an 84.1% yield of cyclohexane at 240 °C was achieved. These findings demonstrate potential applications for the future in promoting and improving industrial catalyst performance. Full article

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7806 KiB

Open AccessArticle

Electronic Structure and Optical Properties of BiOI as a Photocatalyst Driven by Visible Light

by Wen-Wu Dai and Zong-Yan Zhao

Catalysts 2016, 6(9), 133; https://doi.org/10.3390/catal6090133 - 3 Sep 2016

Cited by 29 | Viewed by 8730

Abstract

Bismuth oxyiodide (BiOI) is an important photoelectric functional material that has a wide range of applications. In particular, it can be used as a photocatalyst that shows photocatalytic activity under visible-light irradiation. The synthesis procedure and related photocatalytic performance of BiOI have been [...] Read more.

Bismuth oxyiodide (BiOI) is an important photoelectric functional material that has a wide range of applications. In particular, it can be used as a photocatalyst that shows photocatalytic activity under visible-light irradiation. The synthesis procedure and related photocatalytic performance of BiOI have been reported. However, some of its fundamental properties still need to be further investigated. In this article, density functional theory calculations were performed to investigate the crystal structure, electronic properties, and optical properties of BiOI. Furthermore, the relationship between the intrinsic properties and the photocatalytic performance of BiOI was investigated. Based on the calculated results of the band structure, density of states, and projected wave function, the molecular-orbital bonding structure of BiOI is proposed. As a semiconductor photocatalyst, BiOI shows slight optical anisotropy in the visible-light region, indicating that it can efficiently absorb visible light if the morphology of BiOI is controlled. After comparing several computational methods, it was found that the generalized-gradient approximation corrected for on-site Coulomb interactions (GGA + U) is a suitable computational method for large sized BiOI models (e.g., impurity doping, the surface, and the interface) because it can significantly reduce the computational time while maintaining calculation accuracy. Thus, this article not only provides an in-depth understanding of the fundamental properties of BiOI as a potential efficient photocatalyst driven by visible light, but it also suggests a suitable computational method to investigate these properties. Full article

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1089 KiB

Open AccessCommunication

Synthesis of New Chiral Benzimidazolylidene–Rh Complexes and Their Application in Asymmetric Addition Reactions of Organoboronic Acids to Aldehydes

by Weiping He, Bihui Zhou, Jie Li and Jianyou Shi

Catalysts 2016, 6(9), 132; https://doi.org/10.3390/catal6090132 - 3 Sep 2016

Cited by 8 | Viewed by 4987

Abstract

A series of novel chiral N-heterocyclic carbene rhodium complexes (NHC–Rh) based on benzimidazole have been prepared, and all of the NHC–Rh complexes were fully characterized by NMR and mass spectrometry. These complexes could be used as catalysts for the asymmetric 1,2-addition of [...] Read more.

A series of novel chiral N-heterocyclic carbene rhodium complexes (NHC–Rh) based on benzimidazole have been prepared, and all of the NHC–Rh complexes were fully characterized by NMR and mass spectrometry. These complexes could be used as catalysts for the asymmetric 1,2-addition of organoboronic acids to aldehydes, affording chiral diarylmethanols with high yields and moderate enantioselectivities. Full article

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2920 KiB

Open AccessArticle

Support Screening Studies on the Hydrogenation of Levulinic Acid to γ-Valerolactone in Water Using Ru Catalysts

by Anna Piskun, Jozef G. M. Winkelman, Zhenchen Tang and Hero Jan Heeres

Catalysts 2016, 6(9), 131; https://doi.org/10.3390/catal6090131 - 30 Aug 2016

Cited by 35 | Viewed by 8586

Abstract

γ-Valerolactone (GVL) has been identified as a sustainable platform chemical for the production of carbon-based chemicals. Here we report a screening study on the hydrogenation of levulinic acid (LA) to GVL in water using a wide range of ruthenium supported catalysts in a [...] Read more.

γ-Valerolactone (GVL) has been identified as a sustainable platform chemical for the production of carbon-based chemicals. Here we report a screening study on the hydrogenation of levulinic acid (LA) to GVL in water using a wide range of ruthenium supported catalysts in a batch set-up (1 wt. % Ru, 90 °C, 45 bar of H₂, 2 wt. % catalyst on LA). Eight monometallic catalysts were tested on carbon based(C, carbon nanotubes (CNT)) and inorganic supports (Al₂O₃, SiO₂, TiO₂, ZrO₂, Nb₂O₅ and Beta-12.5). The best result was found for Ru/Beta-12.5 with almost quantitative LA conversion (94%) and 66% of GVL yield after 2 h reaction. The remaining product was 4-hydroxypentanoic acid (4-HPA). Catalytic activity for a bimetallic RuPd/TiO₂ catalyst was by far lower than for the monometallic Ru catalyst (9% conversion after 2 h). The effects of relevant catalyst properties (average Ru nanoparticle size, Brunauer-Emmett-Teller (BET) surface area, micropore area and total acidity) on catalyst activity were assessed. Full article

(This article belongs to the Special Issue Ruthenium Catalysts)

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442 KiB

Open AccessReview

Palladium-Based Catalysts as Electrodes for Direct Methanol Fuel Cells: A Last Ten Years Review

by Juan Carlos Calderón Gómez, Rafael Moliner and Maria Jesus Lázaro

Catalysts 2016, 6(9), 130; https://doi.org/10.3390/catal6090130 - 27 Aug 2016

Cited by 85 | Viewed by 12422

Abstract

Platinum-based materials are accepted as the suitable electrocatalysts for anodes and cathodes in direct methanol fuel cells (DMFCs). Nonetheless, the increased demand and scarce world reserves of Pt, as well as some technical problems associated with its use, have motivated a wide research [...] Read more.

Platinum-based materials are accepted as the suitable electrocatalysts for anodes and cathodes in direct methanol fuel cells (DMFCs). Nonetheless, the increased demand and scarce world reserves of Pt, as well as some technical problems associated with its use, have motivated a wide research focused to design Pd-based catalysts, considering the similar properties between this metal and Pt. In this review, we present the most recent advancements about Pd-based catalysts, considering Pd, Pd alloys with different transition metals and non-carbon supported nanoparticles, as possible electrodes in DMFCs. In the case of the anode, different reported works have highlighted the capacity of these new materials for overcoming the CO poisoning and promote the oxidation of other intermediates generated during the methanol oxidation. Regarding the cathode, the studies have showed more positive onset potentials, as fundamental parameter for determining the mechanism of the oxygen reduction reaction (ORR) and thus, making them able for achieving high efficiencies, with less production of hydrogen peroxide as collateral product. This revision suggests that it is possible to replace the conventional Pt catalysts by Pd-based materials, although several efforts must be made in order to improve their performance in DMFCs. Full article

(This article belongs to the Special Issue Catalysis for Low Temperature Fuel Cells)

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2127 KiB

Open AccessFeature PaperArticle

Controlling Active Site Loop Dynamics in the (β/α)₈ Barrel Enzyme Indole-3-Glycerol Phosphate Synthase

by Kathleen F. O’Rourke, Aneta M. Jelowicki and David D. Boehr

Catalysts 2016, 6(9), 129; https://doi.org/10.3390/catal6090129 - 26 Aug 2016

Cited by 13 | Viewed by 5998

Abstract

The β1α1 loop in the tryptophan biosynthetic enzyme indole-3-glycerol phosphate synthase (IGPS) is important for substrate binding, product release and chemical catalysis. IGPS catalyzes the ring closure of the substrate 1-(o-carboxyphenylamine)-1-dexoyribulose 5-phosphate to form indole-3-glycerol phosphate, involving distinct decarboxylation and dehydration [...] Read more.

The β1α1 loop in the tryptophan biosynthetic enzyme indole-3-glycerol phosphate synthase (IGPS) is important for substrate binding, product release and chemical catalysis. IGPS catalyzes the ring closure of the substrate 1-(o-carboxyphenylamine)-1-dexoyribulose 5-phosphate to form indole-3-glycerol phosphate, involving distinct decarboxylation and dehydration steps. The ring closure step is rate-determining in the thermophilic Sulfolobus sulfataricus enzyme (ssIGPS) at high temperatures. The β1α1 loop is especially important in the dehydration step as it houses the general acid Lys53. We propose that loop dynamics are governed by competing interactions on the N- and C-terminal sides of the loop. We had previously shown that disrupting interactions with the N-terminal side of the loop through the N90A substitution decreases catalytic efficiency, slows down the dehydration step and quenches loop dynamics on the picosecond to millisecond timescales. Here, we show that disrupting interactions on the C-terminal side of the loop through the R64A/D65A substitutions likewise decreases catalytic efficiency, slows down the dehydration step and quenches loop dynamics. Interestingly, the triple substitution R64A/D65A/N90A leads to new μs–ms timescale loop dynamics and makes the ring-closure step rate-determining once again. These results are consistent with a model in which the β1α1 loop is maintained in a structurally dynamic state by these competing interactions, which is important for the dehydration step of catalysis. Competing interactions in other enzymes may likewise keep their loops and other structural elements appropriately mobile. Full article

(This article belongs to the Special Issue Enzyme Catalysis)

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21118 KiB

Open AccessFeature PaperLetter

Organocatalysis: Fundamentals and Comparisons to Metal and Enzyme Catalysis

by Pierre Vogel, Yu-hong Lam, Adam Simon and Kendall N. Houk

Catalysts 2016, 6(9), 128; https://doi.org/10.3390/catal6090128 - 26 Aug 2016

Cited by 37 | Viewed by 18155

Abstract

Catalysis fulfills the promise that high-yielding chemical transformations will require little energy and produce no toxic waste. This message is carried by the study of the evolution of molecular catalysis of some of the most important reactions in organic chemistry. After reviewing the [...] Read more.

Catalysis fulfills the promise that high-yielding chemical transformations will require little energy and produce no toxic waste. This message is carried by the study of the evolution of molecular catalysis of some of the most important reactions in organic chemistry. After reviewing the conceptual underpinnings of catalysis, we discuss the applications of different catalysts according to the mechanism of the reactions that they catalyze, including acyl group transfers, nucleophilic additions and substitutions, and C–C bond forming reactions that employ umpolung by nucleophilic additions to C=O and C=C double bonds. We highlight the utility of a broad range of organocatalysts other than compounds based on proline, the cinchona alkaloids and binaphthyls, which have been abundantly reviewed elsewhere. The focus is on organocatalysts, although a few examples employing metal complexes and enzymes are also included due to their significance. Classical Brønsted acids have evolved into electrophilic hands, the fingers of which are hydrogen donors (like enzymes) or other electrophilic moieties. Classical Lewis base catalysts have evolved into tridimensional, chiral nucleophiles that are N- (e.g., tertiary amines), P- (e.g., tertiary phosphines) and C-nucleophiles (e.g., N-heterocyclic carbenes). Many efficient organocatalysts bear electrophilic and nucleophilic moieties that interact simultaneously or not with both the electrophilic and nucleophilic reactants. A detailed understanding of the reaction mechanisms permits the design of better catalysts. Their construction represents a molecular science in itself, suggesting that sooner or later chemists will not only imitate Nature but be able to catalyze a much wider range of reactions with high chemo-, regio-, stereo- and enantioselectivity. Man-made organocatalysts are much smaller, cheaper and more stable than enzymes. Full article

(This article belongs to the Special Issue Metal-free Organocatalysis)

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5995 KiB

Open AccessFeature PaperArticle

Carbon-Based Air-Breathing Cathodes for Microbial Fuel Cells

by Irene Merino-Jimenez, Carlo Santoro, Santiago Rojas-Carbonell, John Greenman, Ioannis Ieropoulos and Plamen Atanassov

Catalysts 2016, 6(9), 127; https://doi.org/10.3390/catal6090127 - 24 Aug 2016

Cited by 61 | Viewed by 8149

Abstract

A comparison between different carbon-based gas-diffusion air-breathing cathodes for microbial fuel cells (MFCs) is presented in this work. A micro-porous layer (MPL) based on carbon black (CB) and an activated carbon (AC) layer were used as catalysts and applied on different supporting materials, [...] Read more.

A comparison between different carbon-based gas-diffusion air-breathing cathodes for microbial fuel cells (MFCs) is presented in this work. A micro-porous layer (MPL) based on carbon black (CB) and an activated carbon (AC) layer were used as catalysts and applied on different supporting materials, including carbon cloth (CC), carbon felt (CF), and stainless steel (SS) forming cathode electrodes for MFCs treating urine. Rotating ring disk electrode (RRDE) analyses were done on CB and AC to: (i) understand the kinetics of the carbonaceous catalysts; (ii) evaluate the hydrogen peroxide production; and (iii) estimate the electron transfer. CB and AC were then used to fabricate electrodes. Half-cell electrochemical analysis, as well as MFCs continuous power performance, have been monitored. Generally, the current generated was higher from the MFCs with AC electrodes compared to the MPL electrodes, showing an increase between 34% and 61% in power with the AC layer comparing to the MPL. When the MPL was used, the supporting material showed a slight effect in the power performance, being that the CF is more powerful than the CC and the SS. These differences also agree with the electrochemical analysis performed. However, the different supporting materials showed a bigger effect in the power density when the AC layer was used, being the SS the most efficient, with a power generation of 65.6 mW·m⁻², followed by the CC (54 mW·m⁻²) and the CF (44 mW·m⁻²). Full article

(This article belongs to the Special Issue Carbon Materials for Green Catalysis)

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Catalysts, Volume 6, Issue 9 (September 2016) – 21 articles

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