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Catalysts, Volume 2, Issue 3 (September 2012), Pages 327-411

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Editorial

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Open AccessEditorial Photocatalysis—A Special Issue on a Unique Hybrid Area of Catalysis
Catalysts 2012, 2(3), 327-329; doi:10.3390/catal2030327
Received: 7 June 2012 / Revised: 26 July 2012 / Accepted: 30 July 2012 / Published: 9 August 2012
Cited by 2 | PDF Full-text (113 KB) | HTML Full-text | XML Full-text
Abstract An overview of the development of photocatalysis with an identification of contemporary areas of interest. Photocatalysis is placed in the broad field of catalysis. [...] Full article
(This article belongs to the Special Issue Photocatalysts)

Research

Jump to: Editorial

Open AccessArticle Superior MgH2 Kinetics with MgO Addition: A Tribological Effect
Catalysts 2012, 2(3), 330-343; doi:10.3390/catal2030330
Received: 17 July 2012 / Revised: 26 July 2012 / Accepted: 31 July 2012 / Published: 13 August 2012
Cited by 7 | PDF Full-text (922 KB) | HTML Full-text | XML Full-text
Abstract
The kinetics of hydrogen absorption/desorption in magnesium can be improved without any catalysis assistance and MgO was found to be more effective than the best catalyst reported so far, i.e., Nb2O5. Herein, a quantitative analysis of the [...] Read more.
The kinetics of hydrogen absorption/desorption in magnesium can be improved without any catalysis assistance and MgO was found to be more effective than the best catalyst reported so far, i.e., Nb2O5. Herein, a quantitative analysis of the hydrogen kinetics in magnesium modified with MgO was performed in order to identify possible rate controlling mechanisms. While hydrogen absorption was found to be diffusion controlled as commonly reported, hydrogen desorption evolved from nucleation and growth to an interface controlled process depending on the desorption temperature. Comparison with the effect of Nb2O5 indicates that similar rate limiting steps occur regardless of the oxide additive. These findings are reconciled by considering the tribological effect of solid oxide additives, as a correlation between oxides electronegativity and improvement in hydrogen kinetics was found. Such a correlation clearly highlights the mechanical effect of solid oxides in facilitating the grinding and stabilisation of small magnesium particles for efficient and fast hydrogen kinetics. Full article
(This article belongs to the Special Issue Bimetallic Catalysts—Application in Hydrogen Storage)
Open AccessArticle Catalytic Effect of Nb2O5 in MgH2-Nb2O5 Ball-Milled Composites
Catalysts 2012, 2(3), 344-351; doi:10.3390/catal2030344
Received: 23 July 2012 / Revised: 15 August 2012 / Accepted: 29 August 2012 / Published: 10 September 2012
Cited by 3 | PDF Full-text (2322 KB) | HTML Full-text | XML Full-text
Abstract
We report a study on the desorption properties, crystallography and chemical state of MgH2 and 1 mol% Nb2O5 ball-milled composites. Desorption temperatures of the composites decreased with increase of ball-milling time. Size of MgH2 crystallites decreased during [...] Read more.
We report a study on the desorption properties, crystallography and chemical state of MgH2 and 1 mol% Nb2O5 ball-milled composites. Desorption temperatures of the composites decreased with increase of ball-milling time. Size of MgH2 crystallites decreased during ball-milling. Reduction of Nb2O5 after ball-milling was confirmed by tracing the chemical state of Nb and was further supported by TEM observation. The reduced phases may act as more effective catalysts improving the desorption properties. Full article
(This article belongs to the Special Issue Bimetallic Catalysts—Application in Hydrogen Storage)
Open AccessArticle Alumina-Supported Manganese Catalysts for Soot Combustion Prepared by Thermal Decomposition of KMnO4
Catalysts 2012, 2(3), 352-367; doi:10.3390/catal2030352
Received: 23 July 2012 / Revised: 13 August 2012 / Accepted: 16 August 2012 / Published: 11 September 2012
Cited by 1 | PDF Full-text (1534 KB) | HTML Full-text | XML Full-text
Abstract
Alumina-supported manganese catalysts with cryptomelane and/or birnessite structure have been prepared using a simple method based on the thermal decomposition of potassium permanganate. The samples have been characterized by XRD, FTIR, TGA, DSC, N2 adsorption at −196 °C, SEM, H2 [...] Read more.
Alumina-supported manganese catalysts with cryptomelane and/or birnessite structure have been prepared using a simple method based on the thermal decomposition of potassium permanganate. The samples have been characterized by XRD, FTIR, TGA, DSC, N2 adsorption at −196 °C, SEM, H2-TPR and XPS, and their catalytic activity for soot combustion has been tested and compared to that of a reference Pt/alumina catalyst. The thermal decomposition of alumina-supported KMnO4 yields a mixture of supported birnessite and potassium manganate which is the most effective, among those prepared, to lower the soot combustion temperature. However, this material is not useful for soot combustion because the accelerating effect is not based on a catalytic process but on the oxidation of soot by potassium manganate. A suitable soot combustion catalyst is obtained after potassium manganate is removed by water washing, yielding only the birnessite phase on the γ-Al2O3 support. This birnessite phase can be transformed into cryptomelane by calcination at 600 °C. These two samples, γ-Al2O3-supported birnessite and cryptomelane are suitable catalysts for soot combustion in NOx/O2 mixtures, as their catalytic activity is based on the NO2-assited mechanism, that is, both catalysts accelerate the oxidation of NO to NO2 and NO2 promotes soot oxidation. The soot combustion temperatures obtained with these birnessite/cryptomelane alumina-supported catalysts are similar to that obtained with the reference Pt/alumina catalyst. Full article
Open AccessArticle Large Mesopore Generation in an Amorphous Silica-Alumina by Controlling the Pore Size with the Gel Skeletal Reinforcement and Its Application to Catalytic Cracking
Catalysts 2012, 2(3), 368-385; doi:10.3390/catal2030368
Received: 28 June 2012 / Revised: 27 August 2012 / Accepted: 31 August 2012 / Published: 13 September 2012
Cited by 7 | PDF Full-text (1648 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Tetraethoxy orthosilicate (TEOS) was used not only as a precursor of silica, but also as an agent which reinforces the skeleton of silica-gel to prepare an aerogel and resultant silica and silica-alumina with large pore size and pore volume. In this gel [...] Read more.
Tetraethoxy orthosilicate (TEOS) was used not only as a precursor of silica, but also as an agent which reinforces the skeleton of silica-gel to prepare an aerogel and resultant silica and silica-alumina with large pore size and pore volume. In this gel skeletal reinforcement, the strength of silica aerogel skeleton was enhanced by aging with TEOS/2-propanol mixed solution to prevent the shrink of the pores. When silica aerogel was reinforced by TEOS solution, the pore diameter and pore volume of calcined silica could be controlled by the amount of TEOS solution and reached 30 nm and 3.1 cm3/g. The results from N2 adsorption measurement indicated that most of pores for this silica consisted of mesopores. Silica-alumina was prepared by the impregnation of an aluminum tri-sec-butoxide/2-butanol solution with obtained silica. Mixed catalysts were prepared by the combination of β-zeolite (26 wt%) and prepared silica-aluminas with large mesopore (58 wt%) and subsequently the effects of their pore sizes on the catalytic activity and the product selectivity were investigated in catalytic cracking of n-dodecane at 500 °C. The mixed catalysts exhibited not only comparable activity to that for single zeolite, but also unique selectivity where larger amounts of branched products were formed. Full article
(This article belongs to the Special Issue Aerogel Catalyst)
Open AccessArticle Co-Fe-Si Aerogel Catalytic Honeycombs for Low Temperature Ethanol Steam Reforming
Catalysts 2012, 2(3), 386-399; doi:10.3390/catal2030386
Received: 1 August 2012 / Revised: 6 September 2012 / Accepted: 7 September 2012 / Published: 19 September 2012
Cited by 5 | PDF Full-text (1567 KB) | HTML Full-text | XML Full-text
Abstract
Cobalt talc doped with iron (Fe/Co~0.1) and dispersed in SiO2 aerogel was prepared from silica alcogel impregnated with metal nitrates by supercritical drying. Catalytic honeycombs were prepared following the same procedure, with the alcogel synthesized directly over cordierite honeycomb pieces. The [...] Read more.
Cobalt talc doped with iron (Fe/Co~0.1) and dispersed in SiO2 aerogel was prepared from silica alcogel impregnated with metal nitrates by supercritical drying. Catalytic honeycombs were prepared following the same procedure, with the alcogel synthesized directly over cordierite honeycomb pieces. The composite aerogel catalyst was characterized by X-ray diffraction, scanning electron microscopy, focus ion beam, specific surface area and X-ray photoelectron spectroscopy. The catalytic layer is about 8 µm thick and adheres well to the cordierite support. It is constituted of talc layers of about 1.5 µm × 300 nm × 50 nm which are well dispersed and anchored in a SiO2 aerogel matrix with excellent mass-transfer properties. The catalyst was tested in the ethanol steam reforming reaction, aimed at producing hydrogen for on-board, on-demand applications at moderate temperature (573–673 K) and pressure (1–7 bar). Compared to non-promoted cobalt talc, the catalyst doped with iron produces less methane as byproduct, which can only be reformed at high temperature, thereby resulting in higher hydrogen yields. At 673 K and 2 bar, 1.04 NLH2·mLEtOH(l)−1·min−1 are obtained at S/C = 3 and W/F = 390 g·min·molEtOH−1. Full article
(This article belongs to the Special Issue Aerogel Catalyst)
Open AccessArticle Microstructural and Kinetic Evolution of Fe Doped MgH2 during H2 Cycling
Catalysts 2012, 2(3), 400-411; doi:10.3390/catal2030400
Received: 30 July 2012 / Revised: 3 September 2012 / Accepted: 7 September 2012 / Published: 24 September 2012
Cited by 8 | PDF Full-text (4410 KB) | HTML Full-text | XML Full-text
Abstract
The effect of extended H2 sorption cycles on the structure and on the hydrogen storage performances of MgH2 powders with 5 wt% of Fe particle catalyst is reported. MgH2 powders with and without Fe have been ball milled under [...] Read more.
The effect of extended H2 sorption cycles on the structure and on the hydrogen storage performances of MgH2 powders with 5 wt% of Fe particle catalyst is reported. MgH2 powders with and without Fe have been ball milled under Argon, the doped MgH2 nanocomposite has been cycled under hydrogen pressure up to a maximum of 47 desorption and absorption cycles at 300 °C. After acceleration during the first 10 cycles, the kinetics behavior of doped MgH2 is constant after extended cycling, in terms of maximum storage capacity and rate of sorption. The major effect of cycling on particle morphology is the progressive extraction of Mg from the MgO shell surrounding the powder particles. The Mg extraction from the MgO shell leaves the catalyst particles inside the hydride particles. Many empty MgO shells are observed in the pure ball milled MgH2 upon cycling at higher temperature, suggesting that this enhancement of the extraction efficiency is related to the higher operating temperature which favors Mg diffusivity with respect to the H ion one. Full article
(This article belongs to the Special Issue Bimetallic Catalysts—Application in Hydrogen Storage)

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