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Catalysts, Volume 2, Issue 4 (December 2012), Pages 412-601

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Research

Jump to: Review

Open AccessCommunication Alcohol Dehydrogenation with a Dual Site Ruthenium, Boron Catalyst Occurs at Ruthenium
Catalysts 2012, 2(4), 412-421; doi:10.3390/catal2040412
Received: 14 June 2012 / Revised: 27 August 2012 / Accepted: 5 September 2012 / Published: 11 October 2012
Cited by 4 | PDF Full-text (431 KB) | HTML Full-text | XML Full-text
Abstract
The complex [(κ3-(N,N,O-py2B(Me)OH)Ru(NCMe)3]+ TfO (1) is a catalyst for transfer dehydrogenation of alcohols, which was designed to function through a cooperative transition state in which reactivity was split [...] Read more.
The complex [(κ3-(N,N,O-py2B(Me)OH)Ru(NCMe)3]+ TfO (1) is a catalyst for transfer dehydrogenation of alcohols, which was designed to function through a cooperative transition state in which reactivity was split between boron and ruthenium. We show here both stoichiometric and catalytic evidence to support that in the case of alcohol oxidation, the mechanism most likely involves reactivity only at the ruthenium center. Full article
Open AccessArticle Carbon Aerogel-Supported Pt Catalysts for the Hydrogenolysis and Isomerization of n-Butane: Influence of the Carbonization Temperature of the Support and Pt Particle Size
Catalysts 2012, 2(4), 422-433; doi:10.3390/catal2040422
Received: 18 July 2012 / Revised: 3 September 2012 / Accepted: 24 September 2012 / Published: 12 October 2012
Cited by 1 | PDF Full-text (307 KB) | HTML Full-text | XML Full-text
Abstract
Carbon aerogels prepared at different carbonization temperatures and with varying mesopore volumes were used as supports for Pt catalysts to study the n-C4H10/H2 reaction. Mean Pt particle size depended on the mesopore volume of the support, [...] Read more.
Carbon aerogels prepared at different carbonization temperatures and with varying mesopore volumes were used as supports for Pt catalysts to study the n-C4H10/H2 reaction. Mean Pt particle size depended on the mesopore volume of the support, showing a linear decrease when the mesopore volume increased. The turnover frequency (TOF) for hydrogenolysis was much higher than for isomerization in catalysts supported on carbon aerogels obtained at 900–950 °C. However, both TOF values were similar in catalysts supported on the carbon aerogel obtained at 500 °C. TOF for hydrogenolysis and isomerization were related to the mean Pt particle size in catalysts supported on carbon aerogels obtained at 900–950 °C. In addition, both reactions showed a compensation effect between the activation energy and pre-exponential factor, indicating that they have the same intermediate, i.e., the chemisorbed dehydrogenated alkane. Full article
(This article belongs to the Special Issue Aerogel Catalyst)
Open AccessArticle Enhancement of Hydrogen Storage Behavior of Complex Hydrides via Bimetallic Nanocatalysts Doping
Catalysts 2012, 2(4), 434-446; doi:10.3390/catal2040434
Received: 3 July 2012 / Revised: 28 August 2012 / Accepted: 28 September 2012 / Published: 17 October 2012
Cited by 1 | PDF Full-text (971 KB) | HTML Full-text | XML Full-text
Abstract
Pristine complex quaternary hydride (LiBH4/2LiNH2) and its destabilized counterpart (LiBH4/2LiNH2/nanoMgH2) have recently shown promising reversible hydrogen storage capacity under moderate operating conditions. The destabilization of complex hydride via nanocrystalline MgH2 apparently [...] Read more.
Pristine complex quaternary hydride (LiBH4/2LiNH2) and its destabilized counterpart (LiBH4/2LiNH2/nanoMgH2) have recently shown promising reversible hydrogen storage capacity under moderate operating conditions. The destabilization of complex hydride via nanocrystalline MgH2 apparently lowers the thermodynamic heat values and thus enhances the reversible hydrogen storage behavior at moderate temperatures. However, the kinetics of these materials is rather low and needs to be improved for on-board vehicular applications. Nanocatalyst additives such as nano Ni, nano Fe, nano Co, nano Mn and nano Cu at low concentrations on the complex hydride host structures have demonstrated a reduction in the decomposition temperature and overall increase in the hydrogen desorption reaction rates. Bi-metallic nanocatalysts such as the combination of nano Fe and nano Ni have shown further pronounced kinetics enhancement in comparison to their individual counterparts. Additionally, the vital advantage of using bi-metallic nanocatalysts is to enable the synergistic effects and characteristics of the two transitional nanometal species on the host hydride matrix for the optimized hydrogen storage behavior. Full article
(This article belongs to the Special Issue Bimetallic Catalysts—Application in Hydrogen Storage)
Open AccessArticle Carbon Xerogel Catalyst for NO Oxidation
Catalysts 2012, 2(4), 447-465; doi:10.3390/catal2040447
Received: 20 July 2012 / Revised: 28 September 2012 / Accepted: 9 October 2012 / Published: 17 October 2012
Cited by 3 | PDF Full-text (467 KB) | HTML Full-text | XML Full-text
Abstract
Carbon xerogels were prepared by the polycondensation of resorcinol and formaldehyde using three different solution pH values and the gels were carbonized at three different temperatures. Results show that it is possible to tailor the pore texture of carbon xerogels by adjusting [...] Read more.
Carbon xerogels were prepared by the polycondensation of resorcinol and formaldehyde using three different solution pH values and the gels were carbonized at three different temperatures. Results show that it is possible to tailor the pore texture of carbon xerogels by adjusting the pH of the initial solution and the carbonization temperature. Materials with different textural properties were obtained and used as catalysts for NO oxidation at room temperature. The NO conversions obtained with carbon xerogels were quite high, showing that carbon xerogels are efficient catalysts for NO oxidation. A maximum of 98% conversion for NO was obtained at initial concentration of NO of 1000 ppm and 10% of O2. The highest NO conversions were obtained with the samples presenting the highest surface areas. The temperature of reaction has a strong influence on NO oxidation: the conversion of NO decreases with the increase of reaction temperature. Full article
(This article belongs to the Special Issue Aerogel Catalyst)
Open AccessArticle Tailoring Synthesis Conditions of Carbon Xerogels towards Their Utilization as Pt-Catalyst Supports for Oxygen Reduction Reaction (ORR)
Catalysts 2012, 2(4), 466-489; doi:10.3390/catal2040466
Received: 6 August 2012 / Revised: 24 September 2012 / Accepted: 9 October 2012 / Published: 17 October 2012
Cited by 12 | PDF Full-text (881 KB) | HTML Full-text | XML Full-text
Abstract
Carbon xerogels characterized by different textural, structural and chemical properties were synthesized and used as supports for Pt catalysts for the application in polymer electrolyte fuel cells. Synthesis conditions were varied in order to synthesize carbon xerogels following the sol-gel method. These [...] Read more.
Carbon xerogels characterized by different textural, structural and chemical properties were synthesized and used as supports for Pt catalysts for the application in polymer electrolyte fuel cells. Synthesis conditions were varied in order to synthesize carbon xerogels following the sol-gel method. These included the reactants ratio (precursor/formaldehyde), the catalyst concentration (precursor/catalyst ratio) and type (basic and acid), the precursor type (resorcinol and pyrogallol) and the solvent (aqueous or acetone based). Stoichiometric mixtures of resorcinol and formaldehyde yielded well polymerized gels and highly developed structures. Slow gelation, favored by the presence of acetone as solvent in the sol and low catalyst concentration, resulted in higher polymerization extent with a highly mesoporous or even macroporous texture and more ordered structure, as evidenced by XPS and Raman spectroscopy. Small Pt particles of ca. 3.5 nm were obtained by using carbon xerogels characterized by an ordered surface structure. The specific activity towards the oxygen reduction reaction, i.e., the limiting catalytic process in low temperature fuel cells, is significantly favored by highly ordered carbon xerogels due to a metal-support enhanced interaction. Nevertheless, surface defects favor the distribution of the metallic particles on the surface of carbon, which in the end influences the effectiveness of the catalyst. Accelerated degradation tests were conducted to evaluate catalyst stability under potential cycling conditions. The observed decay of performance was considerably lower for the catalysts based on ordered carbon xerogels stabilizing Pt particles in a higher extent than the other xerogels and the commercial carbon black support. Full article
(This article belongs to the Special Issue Aerogel Catalyst)
Open AccessArticle Advantages of the Biomimetic Nanostructured Films as an Immobilization Method vs. the Carbon Paste Classical Method
Catalysts 2012, 2(4), 517-531; doi:10.3390/catal2040517
Received: 27 September 2012 / Revised: 26 October 2012 / Accepted: 1 November 2012 / Published: 9 November 2012
Cited by 3 | PDF Full-text (421 KB) | HTML Full-text | XML Full-text
Abstract
Tyrosinase-based biosensors containing a phthalocyanine as electron mediator have been prepared by two different methods. In the first approach, the enzyme and the electron mediator have been immobilized in carbon paste electrodes. In the second method, they have been introduced in an [...] Read more.
Tyrosinase-based biosensors containing a phthalocyanine as electron mediator have been prepared by two different methods. In the first approach, the enzyme and the electron mediator have been immobilized in carbon paste electrodes. In the second method, they have been introduced in an arachidic acid Langmuir-Blodgett nanostructured film that provides a biomimetic environment. The sensing properties of non-nanostructured and nanostructured biosensors towards catechol, catechin and phenol have been analyzed and compared. The enzyme retains the biocatalytic properties in both matrixes. However, the nanostructured biomimetic films show higher values of maximum reaction rates and lowest apparent Michaelis-Menten constants. In both types of sensors, the sensitivity follows the decreasing order catechol > catechin > phenol. The detection limits observed are in the range of 1.8–5.4 μM for Langmuir-Blodgett biosensors and 8.19–8.57 μM for carbon paste biosensors. In summary, it has been demonstrated that the Langmuir-Blodgett films provide a biomimetic environment and nanostructured biosensors show better performances in terms of kinetic, detection limit and stability. Full article
(This article belongs to the Special Issue Biomimetic Catalysts)
Open AccessArticle Catalytic Studies of Sodium Hydroxide and Carbon Monoxide Reaction
Catalysts 2012, 2(4), 532-543; doi:10.3390/catal2040532
Received: 25 September 2012 / Revised: 5 November 2012 / Accepted: 20 November 2012 / Published: 27 November 2012
Cited by 1 | PDF Full-text (654 KB) | HTML Full-text | XML Full-text
Abstract
We have studied the effect of ball milling on alumina mixed nickel, magnetite and Raney nickel on the reaction: 2NaOH(s) + CO (g) = Na2CO3 (s) + H2 (g) and determined the optimum particle size for the catalysts. [...] Read more.
We have studied the effect of ball milling on alumina mixed nickel, magnetite and Raney nickel on the reaction: 2NaOH(s) + CO (g) = Na2CO3 (s) + H2 (g) and determined the optimum particle size for the catalysts. The best performance was shown by a 2 h ball milled Raney nickel with average crystallite size of 209 Å. This reaction serves the dual purpose of carbon sequestration and yielding hydrogen gas. Full article

Review

Jump to: Research

Open AccessReview Hydrogen Production from Semiconductor-based Photocatalysis via Water Splitting
Catalysts 2012, 2(4), 490-516; doi:10.3390/catal2040490
Received: 4 July 2012 / Revised: 30 August 2012 / Accepted: 28 September 2012 / Published: 17 October 2012
Cited by 58 | PDF Full-text (914 KB) | HTML Full-text | XML Full-text
Abstract
Hydrogen is the ideal fuel for the future because it is clean, energy efficient, and abundant in nature. While various technologies can be used to generate hydrogen, only some of them can be considered environmentally friendly. Recently, solar hydrogen generated via photocatalytic [...] Read more.
Hydrogen is the ideal fuel for the future because it is clean, energy efficient, and abundant in nature. While various technologies can be used to generate hydrogen, only some of them can be considered environmentally friendly. Recently, solar hydrogen generated via photocatalytic water splitting has attracted tremendous attention and has been extensively studied because of its great potential for low-cost and clean hydrogen production. This paper gives a comprehensive review of the development of photocatalytic water splitting for generating hydrogen, particularly under visible-light irradiation. The topics covered include an introduction of hydrogen production technologies, a review of photocatalytic water splitting over titania and non-titania based photocatalysts, a discussion of the types of photocatalytic water-splitting approaches, and a conclusion for the current challenges and future prospects of photocatalytic water splitting. Based on the literatures reported here, the development of highly stable visible–light-active photocatalytic materials, and the design of efficient, low-cost photoreactor systems are the key for the advancement of solar-hydrogen production via photocatalytic water splitting in the future. Full article
(This article belongs to the Special Issue Photocatalysts)
Open AccessReview Conversion of CO2 via Visible Light Promoted Homogeneous Redox Catalysis
Catalysts 2012, 2(4), 544-571; doi:10.3390/catal2040544
Received: 27 August 2012 / Revised: 26 October 2012 / Accepted: 13 November 2012 / Published: 27 November 2012
Cited by 28 | PDF Full-text (556 KB) | HTML Full-text | XML Full-text
Abstract
This review gives an overview on the principles of light-promoted homogeneous redox catalysis in terms of applications in CO2 conversion. Various chromophores and the advantages of different structures and metal centers as well as optimization strategies are discussed. All aspects of [...] Read more.
This review gives an overview on the principles of light-promoted homogeneous redox catalysis in terms of applications in CO2 conversion. Various chromophores and the advantages of different structures and metal centers as well as optimization strategies are discussed. All aspects of the reduction catalyst site are restricted to CO2 conversion. An important focus of this review is the question of a replacement of the sacrificial donor which is found in most of the current publications. Furthermore, electronic parameters of supramolecular systems are reviewed with reference to the requisite of chromophores, oxidation and reduction sites. Full article
(This article belongs to the Special Issue Photocatalysts)
Open AccessReview Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates
Catalysts 2012, 2(4), 572-601; doi:10.3390/catal2040572
Received: 7 October 2012 / Revised: 7 December 2012 / Accepted: 10 December 2012 / Published: 19 December 2012
Cited by 87 | PDF Full-text (1026 KB) | HTML Full-text | XML Full-text
Abstract
Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end [...] Read more.
Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO. Full article
(This article belongs to the Special Issue Photocatalysts)
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