Catalysts

154 KiB

Open AccessCommunication

Cellulases in Ionic Liquids—The Long Term Stability of Aspergillus sp. Cellulase

by Nele Ilmberger, Julia Pottkämper and Wolfgang R. Streit

Catalysts 2013, 3(2), 584-587; https://doi.org/10.3390/catal3020584 - 13 Jun 2013

Cited by 17 | Viewed by 6620

It is a well known fact that some ionic liquids (ILs) have the potential to dissolve crystalline, water-insoluble cellulose that could be used as a source of glucose and subsequently derived molecules. Nevertheless, in the presence of high IL concentrations, cellulase activity and, [...] Read more.

It is a well known fact that some ionic liquids (ILs) have the potential to dissolve crystalline, water-insoluble cellulose that could be used as a source of glucose and subsequently derived molecules. Nevertheless, in the presence of high IL concentrations, cellulase activity and, even more so, cellulase stability are still challenging difficulties that need to be overcome. Therefore four fungal cellulase preparations were assayed in the presence of 30% (v/v) of five different ILs. Thereby the cellulase from Aspergillus sp. (Sigma-Aldrich) was not only remarkably active (up to 28 U/mg in 30% (v/v) IL ([BMMIM]Cl)), but furthermore stayed active during several weeks in the presence of 60% (v/v) IL (up to 50% relative activity after 9 weeks). Full article

(This article belongs to the Special Issue Ionic Liquids in Catalysis)

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1439 KiB

Open AccessArticle

Ni-Based Catalysts for Low Temperature Methane Steam Reforming: Recent Results on Ni-Au and Comparison with Other Bi-Metallic Systems

by Hongjing Wu, Valeria La Parola, Giuseppe Pantaleo, Fabrizio Puleo, Anna M. Venezia and Leonarda F. Liotta

Catalysts 2013, 3(2), 563-583; https://doi.org/10.3390/catal3020563 - 05 Jun 2013

Cited by 135 | Viewed by 17186

Abstract

Steam reforming of light hydrocarbons provides a promising method for hydrogen production. Ni-based catalysts are so far the best and the most commonly used catalysts for steam reforming because of their acceptably high activity and significantly lower cost in comparison with alternative precious [...] Read more.

Steam reforming of light hydrocarbons provides a promising method for hydrogen production. Ni-based catalysts are so far the best and the most commonly used catalysts for steam reforming because of their acceptably high activity and significantly lower cost in comparison with alternative precious metal-based catalysts. However, nickel catalysts are susceptible to deactivation from the deposition of carbon, even when operating at steam-to-carbon ratios predicted to be thermodynamically outside of the carbon-forming regime. Reactivity and deactivation by carbon formation can be tuned by modifying Ni surfaces with a second metal, such as Au through alloy formation. In the present review, we summarize the very recent progress in the design, synthesis, and characterization of supported bimetallic Ni-based catalysts for steam reforming. The progress in the modification of Ni with noble metals (such as Au and Ag) is discussed in terms of preparation, characterization and pretreatment methods. Moreover, the comparison with the effects of other metals (such as Sn, Cu, Co, Mo, Fe, Gd and B) is addressed. The differences of catalytic activity, thermal stability and carbon species between bimetallic and monometallic Ni-based catalysts are also briefly shown. Full article

(This article belongs to the Special Issue New Trends in Gold Catalysts)

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949 KiB

Open AccessArticle

Towards Rational Design of Nanoparticle Catalysis in Ionic Liquids

by Bin Zhang and Ning Yan

Catalysts 2013, 3(2), 543-562; https://doi.org/10.3390/catal3020543 - 05 Jun 2013

Cited by 30 | Viewed by 11653

Abstract

This feature article introduces the strategies on the design of highly efficient nanoparticle (NP) catalytic systems in ionic liquids (ILs). The employment of functional ILs as the media for NP preparation and catalysis could prove advantageous in terms of enhancing both NP stability [...] Read more.

This feature article introduces the strategies on the design of highly efficient nanoparticle (NP) catalytic systems in ionic liquids (ILs). The employment of functional ILs as the media for NP preparation and catalysis could prove advantageous in terms of enhancing both NP stability and catalytic activity. Hydroxyl group functionalized ILs, in particular, exhibited a remarkable promotion effect on a variety of reactions catalyzed by NPs, such as hydrogenation over Rh NPs, hydrodehalogenation over Pt NPs and Suzuki reaction over Pd NPs. In some cases, tailor-made stabilizer is used in addition to keep the NPs sufficiently stable. For example, a carboxylic group modified polyvinylpyrrolidone endows NPs three-fold stabilization, including steric, electrostatic and ligand stabilizations, which leads to excellent stability of the NPs. The catalytic activities of these NPs, on the other hand, are not compromised, as each of these stabilizations is not too strong. Following that, the article describes our recent work on the rational design of bimetallic NPs in ILs and the development of multifunctional systems involving NPs for a tandem reaction sequence that convert lignin-derived phenolic compounds into fuels. Full article

(This article belongs to the Special Issue Ionic Liquids in Catalysis)

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579 KiB

Open AccessArticle

Adaptive Global Carbon Monoxide Kinetic Mechanism over Platinum/Alumina Catalysts

by Christopher Depcik, Sudarshan Loya, Anand Srinivasan, Travis Wentworth and Susan Stagg-Williams

Catalysts 2013, 3(2), 517-542; https://doi.org/10.3390/catal3020517 - 29 May 2013

Cited by 4 | Viewed by 6797

Abstract

Carbon monoxide (CO) oxidation is one of the more widely researched mechanisms given its pertinence across many industrial platforms. Because of this, ample information exists as to the detailed reaction steps in its mechanism. While detailed kinetic mechanisms are more accurate and can [...] Read more.

Carbon monoxide (CO) oxidation is one of the more widely researched mechanisms given its pertinence across many industrial platforms. Because of this, ample information exists as to the detailed reaction steps in its mechanism. While detailed kinetic mechanisms are more accurate and can be written as a function of catalytic material on the surface, global mechanisms are more widely used because of their computational efficiency advantage. This paper merges the theory behind detailed kinetics into a global kinetic model for the singular CO oxidation reaction while formulating expressions that adapt to catalyst properties on the surface such as dispersion and precious metal loading. Results illustrate that the model is able to predict the light-off and extinction temperatures during a hysteresis experiment as a function of different inlet CO concentrations and precious metal dispersion. Full article

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868 KiB

Open AccessArticle

Photocatalytic Degradation of Acridine Orange over NaBiO₃ Driven by Visible Light Irradiation

by Chung-Shin Lu, Chiing-Chang Chen, Ling-Kuen Huang, Peir-An Tsai and Hsiao-Fang Lai

Catalysts 2013, 3(2), 501-516; https://doi.org/10.3390/catal3020501 - 21 May 2013

Cited by 29 | Viewed by 9059

Abstract

The photocatalytic degradation of acridine orange (AO) dye by NaBiO₃ photocatalyst under visible light irradiation was investigated systematically. The NaBiO₃ photocatalyst exhibited a higher photocatalytic activity compared to the P25 photocatalyst. After 160 min of photocatalytic reaction, the degradation rate of [...] Read more.

The photocatalytic degradation of acridine orange (AO) dye by NaBiO₃ photocatalyst under visible light irradiation was investigated systematically. The NaBiO₃ photocatalyst exhibited a higher photocatalytic activity compared to the P25 photocatalyst. After 160 min of photocatalytic reaction, the degradation rate of AO could reach to 99% in appropriate conditions. Factors, such as catalyst dosage, solution pH, initial AO concentration and the presence of anions, were found to influence the degradation rate. To scrutinize the mechanistic details of the dye photodegradation, the intermediates of the processes were separated, identified and characterized by the HPLC-ESI-MS technique. The analytical results indicated that the N-de-methylation degradation of AO dye took place in a stepwise manner to yield mono-, di-, tri- and tetra-N-de-methylated AO species generated during the processes. The probable photodegradation pathways were proposed and discussed. Full article

(This article belongs to the Special Issue Photocatalysts)

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408 KiB

Open AccessArticle

Mechanistic Studies for Synthesis of Bis(indolyl)methanes: Pd-Catalyzed C–H Activation of Indole–Carboxylic Acids with Benzyl Alcohols in Water

by Hidemasa Hikawa, Hideharu Suzuki, Yuusaku Yokoyama and Isao Azumaya

Catalysts 2013, 3(2), 486-500; https://doi.org/10.3390/catal3020486 - 16 May 2013

Cited by 33 | Viewed by 9390

Abstract

A method for synthesis without protecting groups of bis(indolyl)methanes by the (η³-benzyl)palladium system generated from a palladium catalyst and benzyl alcohol in water is developed. This domino protocol involves C3–H bond activation/benzylation of indole–carboxylic acids and benzylic C–H functionalization. Mechanistic studies [...] Read more.

A method for synthesis without protecting groups of bis(indolyl)methanes by the (η³-benzyl)palladium system generated from a palladium catalyst and benzyl alcohol in water is developed. This domino protocol involves C3–H bond activation/benzylation of indole–carboxylic acids and benzylic C–H functionalization. Mechanistic studies indicate that the (η³-benzyl)palladium(II) complex, which is formed via oxidative addition of benzyl alcohol 2 to a Pd(0) species, activates the C–H bond at the C3-position of indole 1. Notably, water plays an important role in our catalytic system for sp³ C–O bond activation and stabilization of OH⁻ by hydration for the smooth generation of the activated Pd(II) cation species, as well as for nucleophilic attack of indoles to hydrated benzyl alcohols. Full article

(This article belongs to the Special Issue Palladium Catalysts for Cross-Coupling Reaction)

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1358 KiB

Open AccessReview

Specific Facets-Dominated Anatase TiO₂: Fluorine-Mediated Synthesis and Photoactivity

by Maria Vittoria Dozzi and Elena Selli

Catalysts 2013, 3(2), 455-485; https://doi.org/10.3390/catal3020455 - 16 May 2013

Cited by 115 | Viewed by 16841

Abstract

Semiconductors crystal facet engineering has become an important strategy for properly tuning and optimizing both the physicochemical properties and the reactivity of photocatalysts. In this review, a concise survey of recent results obtained in the field of specific surface-oriented anatase TiO₂ crystals [...] Read more.

Semiconductors crystal facet engineering has become an important strategy for properly tuning and optimizing both the physicochemical properties and the reactivity of photocatalysts. In this review, a concise survey of recent results obtained in the field of specific surface-oriented anatase TiO₂ crystals preparation is presented. The attention is mainly focused on the fluorine-mediated hydrothermal and/or solvothermal processes employed for the synthesis and the assembly of anatase micro/nanostructures with dominant {001} facets. Their peculiar photocatalytic properties and potential applications are also presented, with a particular focus on photocatalysis-based environmental clean up and solar energy conversion applications. Finally, the most promising results obtained in the engineering of TiO₂ anatase crystal facets obtained by employing alternative, possibly more environmentally friendly methods are critically compared. Full article

(This article belongs to the Special Issue Photocatalysts)

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2682 KiB

Open AccessArticle

Manganese Oxide-Surface Modified Titanium (IV) Dioxide as Environmental Catalyst

by Qiliang Jin, Hiroshi Arimoto, Musashi Fujishima and Hiroaki Tada

Catalysts 2013, 3(2), 444-454; https://doi.org/10.3390/catal3020444 - 23 Apr 2013

Cited by 37 | Viewed by 8787

Abstract

The purpose of this study is to present an “environmental catalyst” possessing both thermocatalytic activity and visible-light activity for the decomposition of organic pollutants. Molecule-sized MnO_x clusters are highly dispersed on the surface of TiO₂ (anatase/rutile = 4/1 w/w [...] Read more.

The purpose of this study is to present an “environmental catalyst” possessing both thermocatalytic activity and visible-light activity for the decomposition of organic pollutants. Molecule-sized MnO_x clusters are highly dispersed on the surface of TiO₂ (anatase/rutile = 4/1 w/w, P-25, Degussa) by the chemisorption-calcination cycle technique using Mn(acac)₃ complex as a precursor (MnO_x/TiO₂). The thermo- and photo-catalytic activities of MnO_x/TiO₂ were studied for the degradation of 2-naphthol used as a model water pollutant. In contrast to the FeO_x/TiO₂ system, MnO_x/TiO₂ exhibits high thermocatalytic activity exceeding those of bulk β-β-MnO₂ and Mn₂O₃. Also, visible-light activity is induced by the surface modification of TiO₂ with MnO_xclusters, whereas its UV-light activity decreases. Full article

(This article belongs to the Special Issue Photocatalysts)

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859 KiB

Open AccessArticle

Generation of Free OH_aq Radicals by Black Light Illumination of Degussa (Evonik) P25 TiO₂ Aqueous Suspensions

by Haidong Liao and Torbjörn Reitberger

Catalysts 2013, 3(2), 418-443; https://doi.org/10.3390/catal3020418 - 16 Apr 2013

Cited by 48 | Viewed by 12112

Abstract

This work demonstrates how formation of strongly chemiluminescent 3-hydroxyphthalic hydrazide by hydroxylation of non-chemiluminescent phthalic hydrazide can be applied as a selective reaction probe to obtain information on authentic hydroxyl radical, i.e., ^•OH_aq, formation, in black light illuminated Degussa [...] Read more.

This work demonstrates how formation of strongly chemiluminescent 3-hydroxyphthalic hydrazide by hydroxylation of non-chemiluminescent phthalic hydrazide can be applied as a selective reaction probe to obtain information on authentic hydroxyl radical, i.e., ^•OH_aq, formation, in black light illuminated Degussa P25 TiO₂ aerated suspensions in the pH range from 3 to 11. The ^•OH_aq formation was found to be strongly pH dependent. At alkaline pH, the apparent quantum efficiency of ^•OH_aq formation was estimated to be at the ~10⁻² level whereas at acidic pH it was near zero. Addition of phosphate and fluoride ions substantially enhanced the ^•OH_aq production in the acidic pH range. It is suggested that ^•OH_aq-radical formation in TiO₂ photocatalysis can occur by oxidation of hydroxyl ions in the water layer adsorbed on TiO₂ surfaces. Full article

(This article belongs to the Special Issue Photocatalysts)

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455 KiB

Open AccessReview

Enzymatic Catalysis at Interfaces—Heterophase Systems as Substrates for Enzymatic Action

by Clemens K. Weiss and Katharina Landfester

Catalysts 2013, 3(2), 401-417; https://doi.org/10.3390/catal3020401 - 09 Apr 2013

Cited by 8 | Viewed by 7600

Abstract

Several important enzymatic reactions occurring in nature, such as, e.g., the digestion of fat, proceed only at the interface of two immiscible phases. Typically, these systems consist of an organic substrate, dispersed in an aqueous continuous phase, with a specialized enzyme capable of [...] Read more.

Several important enzymatic reactions occurring in nature, such as, e.g., the digestion of fat, proceed only at the interface of two immiscible phases. Typically, these systems consist of an organic substrate, dispersed in an aqueous continuous phase, with a specialized enzyme capable of working at the interface. For adopting such a system for organic synthesis, a stable heterophase system with a large interfacial area is required. These prerequisites can be found in so-called miniemulsions. Such liquid-liquid heterophase systems feature droplets with sizes smaller than 500 nm, and more importantly, these emulsions do not suffer from Ostwald ripening, as conventional emulsions do. Consequently, the droplets show long-term stability, even throughout reactions conducted in the droplets. In this review, we will briefly discuss the physicochemical background of miniemulsions, provide a comprehensive overview of the enzymatically catalyzed reactions conducted in miniemulsions and, as data are available, to compare the most important features to conventional systems, as reverse microemulsions, (macro)emulsions and solvent-based systems. Full article

(This article belongs to the Special Issue Biomimetic Catalysts)

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491 KiB

Open AccessReview

Characterization of Active Sites/Entities and Redox/Catalytic Correlations in Copper-Ceria-Based Catalysts for Preferential Oxidation of CO in H₂-Rich Streams

by Arturo Martínez-Arias, Daniel Gamarra, Ana B. Hungría, Marcos Fernández-García, Guillermo Munuera, Aitor Hornés, Parthasarathi Bera, José C. Conesa and Antonio López Cámara

Catalysts 2013, 3(2), 378-400; https://doi.org/10.3390/catal3020378 - 08 Apr 2013

Cited by 60 | Viewed by 8679

Abstract

This article reviews work done at authors’ laboratories about catalysts based on combinations between copper and ceria for preferential oxidation of CO in H₂-rich streams (CO-PROX). The main focus of this review is the characterization of active sites for the process [...] Read more.

This article reviews work done at authors’ laboratories about catalysts based on combinations between copper and ceria for preferential oxidation of CO in H₂-rich streams (CO-PROX). The main focus of this review is the characterization of active sites for the process on the basis of spectroscopic analysis of the systems under reaction conditions (operando techniques). On such a basis, it is exposed the state of the art in this field in connection with results obtained in other laboratories. Full article

(This article belongs to the Special Issue Catalytic Combustion)

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1683 KiB

Open AccessArticle

Visible Light-Photocatalytic Activity of Sulfate-Doped Titanium Dioxide Prepared by the Sol−Gel Method

by Hiromasa Nishikiori, Maki Hayashibe and Tsuneo Fujii

Catalysts 2013, 3(2), 363-377; https://doi.org/10.3390/catal3020363 - 08 Apr 2013

Cited by 38 | Viewed by 7325

Abstract

Sulfate-doped TiO2 was prepared from sol−gel systems containing titaniumalkoxide and sulfuric acid. The time needed for gelation of the systems was significantlyreduced by ultrasonic irradiation. The doped sulfate was observed by FTIR and XPSmeasurements. Some sulfate ions remained in the TiO2 even after [...] Read more.

Sulfate-doped TiO2 was prepared from sol−gel systems containing titaniumalkoxide and sulfuric acid. The time needed for gelation of the systems was significantlyreduced by ultrasonic irradiation. The doped sulfate was observed by FTIR and XPSmeasurements. Some sulfate ions remained in the TiO2 even after heating at 300−600 °C.The UV and visible photocatalytic activities of the samples were confirmed by thedegradation of trichloroethylene (TCE). The activity of the photocatalyst samples duringthe UV irradiation strongly depended on their crystallinities rather than their specificsurface areas, i.e., adsorption ability. The degradation rate during the visible irradiationdepended on both the adsorption ability and visible absorption of the photocatalystsamples. The visible absorption induced by the sulfate-doping was effective for theTCE degradation. Full article

(This article belongs to the Special Issue Photocatalysts)

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Catalysts, Volume 3, Issue 2 (June 2013) – 12 articles , Pages 363-587

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