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Catalysts, Volume 5, Issue 3 (September 2015), Pages 1003-1635

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Editorial

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Open AccessEditorial What’s in a Number?
Catalysts 2015, 5(3), 1304-1305; doi:10.3390/catal5031304
Received: 29 June 2015 / Accepted: 30 June 2015 / Published: 17 July 2015
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Abstract
People like to distill complicated phenomenon into easily digestible numbers. [...] Full article

Research

Jump to: Editorial, Review

Open AccessArticle Synthesis and Electrocatalytic Performance of Multi-Component Nanoporous PtRuCuW Alloy for Direct Methanol Fuel Cells
Catalysts 2015, 5(3), 1003-1015; doi:10.3390/catal5031003
Received: 28 April 2015 / Revised: 27 May 2015 / Accepted: 16 June 2015 / Published: 24 June 2015
Cited by 3 | PDF Full-text (1013 KB) | HTML Full-text | XML Full-text
Abstract
We have prepared a multi-component nanoporous PtRuCuW (np-PtRuCuW) electrocatalyst via a combined chemical dealloying and mechanical alloying process. The X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrochemical measurements have been applied to characterize the microstructure and electrocatalytic activities of the np-PtRuCuW. The
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We have prepared a multi-component nanoporous PtRuCuW (np-PtRuCuW) electrocatalyst via a combined chemical dealloying and mechanical alloying process. The X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrochemical measurements have been applied to characterize the microstructure and electrocatalytic activities of the np-PtRuCuW. The np-PtRuCuW catalyst has a unique three-dimensional bi-continuous ligament structure and the length scale is 2.0 ± 0.3 nm. The np-PtRuCuW catalyst shows a relatively high level of activity normalized to mass (467.1 mA mgPt1) and electrochemically active surface area (1.8 mA cm2) compared to the state-of-the-art commercial PtC and PtRu catalyst at anode. Although the CO stripping peak of np-PtRuCuW 0.47 V (vs. saturated calomel electrode, SCE) is more positive than PtRu, there is a 200 mV negative shift compared to PtC (0.67 V vs. SCE). In addition, the half-wave potential and specific activity towards oxygen reduction of np-PtRuCuW are 0.877 V (vs. reversible hydrogen electrode, RHE) and 0.26 mA cm−2, indicating a great enhancement towards oxygen reduction than the commercial PtC. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
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Open AccessArticle Improving the Ethanol Oxidation Activity of Pt-Mn Alloys through the Use of Additives during Deposition
Catalysts 2015, 5(3), 1016-1033; doi:10.3390/catal5031016
Received: 15 May 2015 / Revised: 11 June 2015 / Accepted: 16 June 2015 / Published: 25 June 2015
Cited by 3 | PDF Full-text (1188 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this work, sodium citrate (SC) was used as an additive to control the particle size and dispersion of Pt-Mn alloy nanoparticles deposited on a carbon support. SC was chosen, since it was the only additive tested that did not prevent Mn from
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In this work, sodium citrate (SC) was used as an additive to control the particle size and dispersion of Pt-Mn alloy nanoparticles deposited on a carbon support. SC was chosen, since it was the only additive tested that did not prevent Mn from co-depositing with Pt. The influence of solution pH during deposition and post-deposition heat treatment on the physical and electrochemical properties of the Pt-Mn alloy was examined. It was determined that careful control over pH is required, since above a pH of four, metal deposition was suppressed. Below pH 4, the presence of sodium citrate reduced the particle size and improved the particle dispersion. This also resulted in larger electrochemically-active surface areas and greater activity towards the ethanol oxidation reaction (EOR). Heat treatment of catalysts prepared using the SC additive led to a significant enhancement in EOR activity, eclipsing the highest activity of our best Pt-Mn/C prepared in the absence of SC. XRD studies verified the formation of the Pt-Mn intermetallic phase upon heat treatment. Furthermore, transmission electron microscopy studies revealed that catalysts prepared using the SC additive were more resistant to particle size growth during heat treatment. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Polyaniline-Derived Ordered Mesoporous Carbon as an Efficient Electrocatalyst for Oxygen Reduction Reaction
Catalysts 2015, 5(3), 1034-1045; doi:10.3390/catal5031034
Received: 12 May 2015 / Revised: 12 June 2015 / Accepted: 19 June 2015 / Published: 26 June 2015
Cited by 12 | PDF Full-text (2414 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Nitrogen-doped ordered mesoporous carbon was synthesized by using polyaniline as the carbon source and SBA-15 as the template. The microstructure, composition and electrochemical behavior were extensively investigated by the nitrogen sorption isotherm, X-ray photoelectron spectroscopy, cyclic voltammetry and rotating ring-disk electrode. It is
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Nitrogen-doped ordered mesoporous carbon was synthesized by using polyaniline as the carbon source and SBA-15 as the template. The microstructure, composition and electrochemical behavior were extensively investigated by the nitrogen sorption isotherm, X-ray photoelectron spectroscopy, cyclic voltammetry and rotating ring-disk electrode. It is found that the pyrolysis temperature yielded a considerable effect on the pore structure, elemental composition and chemical configuration. The pyrolysis temperature from 800 to 1100 °C yielded a volcano-shape relationship with both the specific surface area and the content of the nitrogen-activated carbon. Electrochemical tests showed that the electrocatalytic activity followed a similar volcano-shape relationship, and the carbon catalyst synthesized at 1000 °C yielded the best performance. The post-treatment in NH3 was found to further increase the specific surface area and to enhance the nitrogen doping, especially the edge-type nitrogen, which favored the oxygen reduction reaction in both acid and alkaline media. The above findings shed light on electrocatalysis and offer more strategies for the controllable synthesis of the doped carbon catalyst. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Novel Mesoporous Carbon Supports for PEMFC Catalysts
Catalysts 2015, 5(3), 1046-1067; doi:10.3390/catal5031046
Received: 15 May 2015 / Revised: 18 June 2015 / Accepted: 18 June 2015 / Published: 29 June 2015
Cited by 8 | PDF Full-text (12370 KB) | HTML Full-text | XML Full-text
Abstract
Over the past decade; a significant amount of research has been performed on novel carbon supports for use in proton exchange membrane fuel cells (PEMFCs). Specifically, carbon nanotubes, ordered mesoporous carbon, and colloid imprinted carbons have shown great promise for improving the activity
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Over the past decade; a significant amount of research has been performed on novel carbon supports for use in proton exchange membrane fuel cells (PEMFCs). Specifically, carbon nanotubes, ordered mesoporous carbon, and colloid imprinted carbons have shown great promise for improving the activity and/or stability of Pt-based nanoparticle catalysts. In this work, a brief overview of these materials is given, followed by an in-depth discussion of our recent work highlighting the importance of carbon wall thickness when designing novel carbon supports for PEMFC applications. Four colloid imprinted carbons (CICs) were synthesized using a silica colloid imprinting method, with the resulting CICs having pores of 15 (CIC-15), 26 (CIC-26), 50 (CIC-50) and 80 (CIC-80) nm. These four CICs were loaded with 10 wt. % Pt and then evaluated as oxygen reduction (ORR) catalysts for use in proton exchange membrane fuel cells. To gain insight into the poorer performance of Pt/CIC-26 vs. the other three Pt/CICs, TEM tomography was performed, indicating that CIC-26 had much thinner walls (0–3 nm) than the other CICs and resulting in a higher resistance (leading to distributed potentials) through the catalyst layer during operation. This explanation for the poorer performance of Pt/CIC-26 was supported by theoretical calculations, suggesting that the internal wall thickness of these nanoporous CICs is critical to the future design of porous carbon supports. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Preparation and Electrocatalytic Characteristics of PdW/C Catalyst for Ethanol Oxidation
Catalysts 2015, 5(3), 1068-1078; doi:10.3390/catal5031068
Received: 12 May 2015 / Revised: 12 June 2015 / Accepted: 15 June 2015 / Published: 29 June 2015
Cited by 3 | PDF Full-text (5847 KB) | HTML Full-text | XML Full-text
Abstract
A series of PdW alloy supported on Vulcan XC-72 Carbon (PdW/C) with total 20 wt. % as electrocatalyst are prepared for ethanol oxidation by an ethylene glycol assisted method. Transmission electron microscopy (TEM) characterization shows that PdW nanoparticles with an average size of
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A series of PdW alloy supported on Vulcan XC-72 Carbon (PdW/C) with total 20 wt. % as electrocatalyst are prepared for ethanol oxidation by an ethylene glycol assisted method. Transmission electron microscopy (TEM) characterization shows that PdW nanoparticles with an average size of 3.6 nm are well dispersed on the surface of Vulcan XC-72 Carbon. It is found that the catalytic activity and stability of the PdW/C catalysts are strongly dependent on Pd/W ratios, an optimal Pd/W composition at 1/1 ratio revealed the highest catalytic activity toward ethanol oxidation, which is much better than commercial Pd/C catalysts. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Microwave Synthesis of High Activity FeSe2/C Catalyst toward Oxygen Reduction Reaction
Catalysts 2015, 5(3), 1079-1091; doi:10.3390/catal5031079
Received: 16 May 2015 / Revised: 18 June 2015 / Accepted: 23 June 2015 / Published: 30 June 2015
Cited by 11 | PDF Full-text (5988 KB) | HTML Full-text | XML Full-text
Abstract
The carbon supported iron selenide catalysts (FeSe2/C) were prepared with various selenium to iron ratios (Se/Fe), namely, Se/Fe = 2.0, 2.5, 3.0, 3.5 and 4.0, through facile microwave route by using ferrous oxalate (FeC2O4·2H2O) and
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The carbon supported iron selenide catalysts (FeSe2/C) were prepared with various selenium to iron ratios (Se/Fe), namely, Se/Fe = 2.0, 2.5, 3.0, 3.5 and 4.0, through facile microwave route by using ferrous oxalate (FeC2O4·2H2O) and selenium dioxide (SeO2) as precursors. Accordingly, effects of Se/Fe ratio on the crystal structure, crystallite size, microstructure, surface composition and electrocatalytic activity for oxygen reduction reaction (ORR) of FeSe2/C in an alkaline medium were systematically investigated. The results revealed that all the FeSe2/C catalysts obtained with the Se/Fe ratios of 2.0–4.0 exhibited almost pure orthogonal FeSe2 structure with the estimated mean crystallite sizes of 32.9–36.2 nm. The electrocatalytic activities in potassium hydroxide solutions were higher than those in perchloric acid solutions, and two peak potentials or two plateaus responded to ORR were observed from cyclic voltammograms and polarization curves, respectively. The ORR potentials of 0.781–0.814 V with the electron transfer numbers of 3.3–3.9 at 0.3 V could be achieved as the Se/Fe ratios varied from 2.0 to 4.0. The Fe and Se were presented at the surface of FeSe2/C upon further reduction on FeSe2. The Se/Fe ratios slightly influenced the degree of graphitization in carbon support and the amount of active sites for ORR. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Continuous Catalytic Hydrodeoxygenation of Guaiacol over Pt/SiO2 and Pt/H-MFI-90
Catalysts 2015, 5(3), 1152-1166; doi:10.3390/catal5031152
Received: 28 April 2015 / Revised: 17 June 2015 / Accepted: 19 June 2015 / Published: 3 July 2015
Cited by 7 | PDF Full-text (6718 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Hydrodeoxygenation of guaiacol in the presence of 1-octanol was studied in a fixed-bed reactor under mild conditions (50–250 °C) over platinum particles supported on silica (Pt/SiO2) and a zeolite with framework type MFI at a Si/Al-ratio of 45 (Pt/H-MFI-90). The deoxygenation
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Hydrodeoxygenation of guaiacol in the presence of 1-octanol was studied in a fixed-bed reactor under mild conditions (50–250 °C) over platinum particles supported on silica (Pt/SiO2) and a zeolite with framework type MFI at a Si/Al-ratio of 45 (Pt/H-MFI-90). The deoxygenation selectivity strongly depended on the support and the temperature. Both guaiacol and octanol were rapidly deoxygenated in the presence of hydrogen over Pt/H-MFI-90 at 250 °C to cyclohexane and octane, respectively. In contrast, Pt/SiO2 mostly showed hydrogenation, but hardly any deoxygenation activity. The acidic sites of the MFI-90 support lead to improved deoxygenation performance at the mild temperature conditions of this study. Significant conversions under reaction conditions applied already occurred at temperatures of 200 °C. However, during long-term stability tests, the Pt/H-MFI-90 catalyst deactivated after more than 30 h, probably due to carbon deposition, whereas Pt/SiO2 was more stable. The catalytic activity of the zeolite catalyst could only partly be regained by calcination in air, as some of the acidic sites were lost. Full article
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Open AccessArticle Pt Monolayer Electrocatalyst for Oxygen Reduction Reaction on Pd-Cu Alloy: First-Principles Investigation
Catalysts 2015, 5(3), 1193-1201; doi:10.3390/catal5031193
Received: 30 May 2015 / Revised: 25 June 2015 / Accepted: 26 June 2015 / Published: 6 July 2015
Cited by 3 | PDF Full-text (971 KB) | HTML Full-text | XML Full-text
Abstract
First principles approach is used to examine geometric and electronic structure of the catalyst concept aimed to improve activity and utilization of precious Pt metal for oxygen reduction reaction in fuel cells. The Pt monolayers on Pd skin and Pd1-xCux
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First principles approach is used to examine geometric and electronic structure of the catalyst concept aimed to improve activity and utilization of precious Pt metal for oxygen reduction reaction in fuel cells. The Pt monolayers on Pd skin and Pd1-xCux inner core for various compositions x were examined by building the appropriate models starting from Pd-Cu solid solution. We provided a detailed description of changes in the descriptors of catalytic behavior, d-band energy and binding energies of reaction intermediates, giving an insight into the underlying mechanism of catalytic activity enhancement based on the first principles density functional theory (DFT) calculations. Structural properties of the Pd-Cu bimetallic were determined for bulk and surfaces, including the segregation profile of Cu under different environment on the surface. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessCommunication Surfactant-Template Preparation of Polyaniline Semi-Tubes for Oxygen Reduction
Catalysts 2015, 5(3), 1202-1210; doi:10.3390/catal5031202
Received: 13 May 2015 / Revised: 23 June 2015 / Accepted: 1 July 2015 / Published: 7 July 2015
Cited by 6 | PDF Full-text (1032 KB) | HTML Full-text | XML Full-text
Abstract
Nitrogen and metal doped nanocarbons derived from polyaniline (PANI) have been widely explored as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. In this work, we report surfactant-template synthesis of PANI nanostructures and the ORR electrocatalysts derived from them. By using
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Nitrogen and metal doped nanocarbons derived from polyaniline (PANI) have been widely explored as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. In this work, we report surfactant-template synthesis of PANI nanostructures and the ORR electrocatalysts derived from them. By using cationic surfactant such as the cetyl trimethyl ammonium bromide (CTAB) as the template and the negatively charged persulfate ions as the oxidative agent to stimulate the aniline polymerization in the micelles of CTAB, PANI with a unique 1-D semi-tubular structure can be obtained. The semi-tubular structure can be maintained even after high-temperature treatment at 900 °C, which yields materials exhibiting promising ORR activity. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Positive Effect of Heat Treatment on Carbon-Supported CoS Nanocatalysts for Oxygen Reduction Reaction
Catalysts 2015, 5(3), 1211-1220; doi:10.3390/catal5031211
Received: 7 May 2015 / Revised: 25 June 2015 / Accepted: 29 June 2015 / Published: 15 July 2015
Cited by 5 | PDF Full-text (10130 KB) | HTML Full-text | XML Full-text
Abstract
It is of increasing interest and an important challenge to develop highly efficient less-expensive cathode catalysts for anion-exchange membrane fuel cells (AEMFCs). In this work, we have directly prepared a carbon-supported CoS nanocatalyst in a solvothermal route and investigated the effect of heat-treatment
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It is of increasing interest and an important challenge to develop highly efficient less-expensive cathode catalysts for anion-exchange membrane fuel cells (AEMFCs). In this work, we have directly prepared a carbon-supported CoS nanocatalyst in a solvothermal route and investigated the effect of heat-treatment on electrocatalytic activity and long-term stability using rotating ring-disk electrode (RRDE). The results show that the heat-treatment below 400 °C under nitrogen atmosphere significantly enhanced the electrocatalytic performance of CoS catalyst as a function of annealed temperature in terms of the cathodic current density, the half-wave potential, the HO2 product and the number of electrons transferred. The CoS catalyst that annealed at 400 °C (CoS-400) has exhibited a promising performance with the half-wave potential of 0.71 V vs. RHE (the highest one for non-precious metal chalcogenides), the minimum HO2 product of 4.3% at 0.60 V vs. RHE and close to the 4-electron pathway during the oxygen reduction reaction in 0.1 M KOH. Also, the CoS-400 catalyst has comparable durability to the Pt/C catalyst. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Facile Electrodeposition of Flower-Like PMo12-Pt/rGO Composite with Enhanced Electrocatalytic Activity towards Methanol Oxidation
Catalysts 2015, 5(3), 1275-1288; doi:10.3390/catal5031275
Received: 15 May 2015 / Revised: 7 July 2015 / Accepted: 8 July 2015 / Published: 17 July 2015
Cited by 3 | PDF Full-text (1389 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A facile, rapid and green method based on potentiostatic electrodeposition is developed to synthesize a novel H3PMo12O40-Pt/reduced graphene oxide (denoted as PMo12-Pt/rGO) composite. The as-prepared PMo12-Pt/rGO is characterized by X-ray diffraction (XRD), scanning
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A facile, rapid and green method based on potentiostatic electrodeposition is developed to synthesize a novel H3PMo12O40-Pt/reduced graphene oxide (denoted as PMo12-Pt/rGO) composite. The as-prepared PMo12-Pt/rGO is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results reveal that graphene oxide (GO) is reduced to the rGO by electrochemical method and POMs clusters are successfully located on the rGO as the modifier. Furthermore, the PMo12-Pt/rGO composite shows higher electrocatalytic activity, better tolerance towards CO and better stability than the conventional pure Pt catalyst. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
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Open AccessArticle Titanium-Niobium Oxides as Non-Noble Metal Cathodes for Polymer Electrolyte Fuel Cells
Catalysts 2015, 5(3), 1289-1303; doi:10.3390/catal5031289
Received: 2 June 2015 / Revised: 11 July 2015 / Accepted: 14 July 2015 / Published: 17 July 2015
Cited by 4 | PDF Full-text (8126 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In order to develop noble-metal- and carbon-free cathodes, titanium-niobium oxides were prepared as active materials for oxide-based cathodes and the factors affecting the oxygen reduction reaction (ORR) activity were evaluated. The high concentration sol-gel method was employed to prepare the precursor. Heat treatment
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In order to develop noble-metal- and carbon-free cathodes, titanium-niobium oxides were prepared as active materials for oxide-based cathodes and the factors affecting the oxygen reduction reaction (ORR) activity were evaluated. The high concentration sol-gel method was employed to prepare the precursor. Heat treatment in Ar containing 4% H2 at 700–900 °C was effective for conferring ORR activity to the oxide. Notably, the onset potential for the ORR of the catalyst prepared at 700 °C was approximately 1.0 V vs. RHE, resulting in high quality active sites for the ORR. X-ray (diffraction and photoelectron spectroscopic) analyses and ionization potential measurements suggested that localized electronic energy levels were produced via heat treatment under reductive atmosphere. Adsorption of oxygen molecules on the oxide may be governed by the localized electronic energy levels produced by the valence changes induced by substitutional metal ions and/or oxygen vacancies. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
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Open AccessArticle Effect of Microgravity on Synthesis of Nano Ceria
Catalysts 2015, 5(3), 1306-1320; doi:10.3390/catal5031306
Received: 19 May 2015 / Revised: 8 July 2015 / Accepted: 14 July 2015 / Published: 20 July 2015
Cited by 2 | PDF Full-text (11061 KB) | HTML Full-text | XML Full-text
Abstract
Cerium oxide (CeO2) was prepared using a controlled-precipitation method under microgravity at the International Space Station (ISS). For comparison, ceria was also synthesized under normal-gravity conditions (referred as control). The Brunauer-Emmett-Teller (BET) surface area, pore volume and pore size analysis results
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Cerium oxide (CeO2) was prepared using a controlled-precipitation method under microgravity at the International Space Station (ISS). For comparison, ceria was also synthesized under normal-gravity conditions (referred as control). The Brunauer-Emmett-Teller (BET) surface area, pore volume and pore size analysis results indicated that the ceria particles grown in space had lower surface area and pore volume compared to the control samples. Furthermore, the space samples had a broader pore size distribution ranging from 30–600 Å, whereas the control samples consisted of pore sizes from 30–50 Å range. Structural information of the ceria particles were obtained using TEM and XRD. Based on the TEM images, it was confirmed that the space samples were predominantly nano-rods, on the other hand, only nano-polyhedra particles were seen in the control ceria samples. The average particle size was larger for ceria samples synthesized in space. XRD results showed higher crystallinity as well as larger mean crystal size for the space samples. The effect of sodium hydroxide concentration on synthesis of ceria was also examined using 1 M and 3 M solutions. It was found that the control samples, prepared in 1 M and 3 M sodium hydroxide solutions, did not show a significant difference between the two. However, when the ceria samples were prepared in a more basic medium (3 M) under microgravity, a decrease in the particle size of the nano-rods and appearances of nano-polyhedra and spheres were observed. Full article
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Open AccessArticle Pt Monolayer Shell on Nitrided Alloy Core—A Path to Highly Stable Oxygen Reduction Catalyst
Catalysts 2015, 5(3), 1321-1332; doi:10.3390/catal5031321
Received: 15 May 2015 / Revised: 7 July 2015 / Accepted: 13 July 2015 / Published: 22 July 2015
Cited by 10 | PDF Full-text (6339 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The inadequate activity and stability of Pt as a cathode catalyst under the severe operation conditions are the critical problems facing the application of the proton exchange membrane fuel cell (PEMFC). Here we report on a novel route to synthesize highly active and
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The inadequate activity and stability of Pt as a cathode catalyst under the severe operation conditions are the critical problems facing the application of the proton exchange membrane fuel cell (PEMFC). Here we report on a novel route to synthesize highly active and stable oxygen reduction catalysts by depositing Pt monolayer on a nitrided alloy core. The prepared PtMLPdNiN/C catalyst retains 89% of the initial electrochemical surface area after 50,000 cycles between potentials 0.6 and 1.0 V. By correlating electron energy-loss spectroscopy and X-ray absorption spectroscopy analyses with electrochemical measurements, we found that the significant improvement of stability of the PtMLPdNiN/C catalyst is caused by nitrogen doping while reducing the total precious metal loading. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Effect of ZIF-8 Crystal Size on the O2 Electro-Reduction Performance of Pyrolyzed Fe–N–C Catalysts
Catalysts 2015, 5(3), 1333-1351; doi:10.3390/catal5031333
Received: 26 June 2015 / Revised: 16 July 2015 / Accepted: 17 July 2015 / Published: 24 July 2015
Cited by 11 | PDF Full-text (2153 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The effect of ZIF-8 crystal size on the morphology and performance of Fe–N–C catalysts synthesized via the pyrolysis of a ferrous salt, phenanthroline and the metal-organic framework ZIF-8 is investigated in detail. Various ZIF-8 samples with average crystal size ranging from 100 to
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The effect of ZIF-8 crystal size on the morphology and performance of Fe–N–C catalysts synthesized via the pyrolysis of a ferrous salt, phenanthroline and the metal-organic framework ZIF-8 is investigated in detail. Various ZIF-8 samples with average crystal size ranging from 100 to 1600 nm were prepared. The process parameters allowing a templating effect after argon pyrolysis were investigated. It is shown that the milling speed, used to prepare catalyst precursors, and the heating mode, used for pyrolysis, are critical factors for templating nano-ZIFs into nano-sized Fe–N–C particles with open porosity. Templating could be achieved when combining a reduced milling speed with a ramped heating mode. For templated Fe–N–C materials, the performance and activity improved with decreased ZIF-8 crystal size. With the Fe–N–C catalyst templated from the smallest ZIF-8 crystals, the current densities in H2/O2 polymer electrolyte fuel cell at 0.5 V reached ca. 900 mA cm2, compared to only ca. 450 mA cm2 with our previous approach. This templating process opens the path to a morphological control of Fe–N–C catalysts derived from metal-organic frameworks which, when combined with the versatility of the coordination chemistry of such materials, offers a platform for the rational design of optimized Metal–N–C catalysts. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Iron Fischer-Tropsch Catalysts Prepared by Solvent-Deficient Precipitation (SDP): Effects of Washing, Promoter Addition Step, and Drying Temperature
Catalysts 2015, 5(3), 1352-1374; doi:10.3390/catal5031352
Received: 10 April 2015 / Revised: 5 July 2015 / Accepted: 15 July 2015 / Published: 24 July 2015
Cited by 4 | PDF Full-text (8864 KB) | HTML Full-text | XML Full-text
Abstract
A novel, solvent-deficient precipitation (SDP) method for catalyst preparation in general and for preparation of iron FT catalysts in particular is reported. Eight catalysts using a 23 factorial design of experiments to identify the key preparation variables were prepared. The catalysts were
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A novel, solvent-deficient precipitation (SDP) method for catalyst preparation in general and for preparation of iron FT catalysts in particular is reported. Eight catalysts using a 23 factorial design of experiments to identify the key preparation variables were prepared. The catalysts were characterized by electron microprobe, N2 adsorption, TEM, XRD, and ICP. Results show that the morphology of the catalysts, i.e., surface area, pore volume, pore size distribution, crystallite sizes, and promoter distribution are significantly influenced by (1) whether or not the precursor catalyst is washed, (2) the promoter addition step, and (3) the drying condition (temperature). Consequently, the activity, selectivity, and stability of the catalysts determined from fixed-bed testing are also affected by these three variables. Unwashed catalysts prepared by a one-step method and dried at 100 °C produced the most active catalysts for FT synthesis. The catalysts of this study prepared by SDP compared favorably in activity, productivity, and stability with Fe FT catalysts reported in the literature. It is believed that this facile SDP approach has promise for development of future FT catalysts, and also offers a potential alternate route for the preparation of other catalysts for various other applications. Full article
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Open AccessArticle Simple Preparation of Pd Core Nanoparticles for Pd Core/Pt Shell Catalyst and Evaluation of Activity and Durability for Oxygen Reduction Reaction
Catalysts 2015, 5(3), 1375-1387; doi:10.3390/catal5031375
Received: 18 May 2015 / Revised: 14 July 2015 / Accepted: 18 July 2015 / Published: 28 July 2015
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Abstract
Pd core nanoparticles less than 5 nm in mean size were prepared on carbon black (CB) without any stabilizer by using palladium acetate as a precursor and CO as a reducing agent, and then used for preparing Pd core/Pt shell nanoparticles-loaded CB (Pt/Pd/CB).
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Pd core nanoparticles less than 5 nm in mean size were prepared on carbon black (CB) without any stabilizer by using palladium acetate as a precursor and CO as a reducing agent, and then used for preparing Pd core/Pt shell nanoparticles-loaded CB (Pt/Pd/CB). The mean size of Pd nanoparticles could be controlled by the concentration of palladium acetate and the CO bubbling time. The cyclic voltammograms of two Pd nanoparticles-loaded CB (Pd4.2/CB, Pd3.3/CB) electrodes whose mean size was 4.2 and 3.3 nm, respectively, had characteristics similar to a Pt electrode after the formation of a Pt monolayer shell, suggesting that the Pd core nanoparticles were almost covered with the Pt monolayer shell. The oxygen reduction reaction (ORR) on both Pt/Pd/CB proceeded in 4-electron reduction mechanism. Both Pt/Pd/CB electrodes was ca. 1.5 times higher in ORR activity per electrochemical surface area of Pt (specific activity, SA) than the commercial Pt nanoparticles-loaded CB (Tanaka Kikinzoku Kogyo, Pt/CB-TKK) electrode, and the Pt/Pd3.3/CB electrode had higher SA than the Pt/Pd4.2/CB electrode. The ORR activity per unit mass of Pt for both Pt/Pd/CB electrodes was 5.0 and 5.5 times as high as that for the Pt/CB-TKK electrode, respectively. The durability of both Pt/Pd/CB electrodes was comparable to that of Pt/CB-TKK. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle Sb Surface Modification of Pd by Mimetic Underpotential Deposition for Formic Acid Oxidation
Catalysts 2015, 5(3), 1388-1398; doi:10.3390/catal5031388
Received: 13 May 2015 / Revised: 22 July 2015 / Accepted: 22 July 2015 / Published: 28 July 2015
Cited by 1 | PDF Full-text (449 KB) | HTML Full-text | XML Full-text
Abstract
The newly proposed mimetic underpotential deposition (MUPD) technique was extended to modify Pd surfaces with Sb through immersing a Pd film electrode or dispersing Pd/C powder in a Sb(III)-containing solution blended with ascorbic acid (AA). The introduction of AA shifts down the open
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The newly proposed mimetic underpotential deposition (MUPD) technique was extended to modify Pd surfaces with Sb through immersing a Pd film electrode or dispersing Pd/C powder in a Sb(III)-containing solution blended with ascorbic acid (AA). The introduction of AA shifts down the open circuit potential of Pd substrate available to achieve suitable Sb modification. The electrocatalytic activity and long-term stability towards HCOOH electrooxidation of the Sb modified Pd surfaces (film electrode or powder catalyst) by MUPD is superior than that of unmodified Pd and Sb modified Pd surfaces by conventional UPD method. The enhancement of electrocatalytic performance is due to the third body effect and electronic effect, as well as bi-functional mechanism induced by Sb modification which result in increased resistance against CO poisoning. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessArticle The Use of C-MnO2 as Hybrid Precursor Support for a Pt/C-MnxO1+x Catalyst with Enhanced Activity for the Methanol Oxidation Reaction (MOR)
Catalysts 2015, 5(3), 1399-1416; doi:10.3390/catal5031399
Received: 23 May 2015 / Revised: 17 July 2015 / Accepted: 22 July 2015 / Published: 30 July 2015
Cited by 7 | PDF Full-text (1318 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Platinum (Pt) nanoparticles are deposited on a hybrid support (C-MnO2) according to a polyol method. The home-made catalyst, resulted as Pt/C-MnxO1+x, is compared with two different commercial platinum based materials (Pt/C and PtRu/C). The synthesized catalyst
[...] Read more.
Platinum (Pt) nanoparticles are deposited on a hybrid support (C-MnO2) according to a polyol method. The home-made catalyst, resulted as Pt/C-MnxO1+x, is compared with two different commercial platinum based materials (Pt/C and PtRu/C). The synthesized catalyst is characterized by means of FESEM, XRD, ICP-MS, XPS and μRS analyses. MnO2 is synthesized and deposited over a commercial grade of carbon (Vulcan XC72) by facile reduction of potassium permanganate in acidic solution. Pt nanoparticles are synthesized on the hybrid support by a polyol thermal assisted method (microwave irradiation), followed by an annealing at 600 °C. The obtained catalyst displays a support constituted by a mixture of manganese oxides (Mn2O3 and Mn3O4) with a Pt loading of 19 wt. %. The electro-catalytic activity towards MOR is assessed by RDE in acid conditions (0.5 M H2SO4), evaluating the ability to oxidize methanol in 1 M concentration. The synthesized Pt/C-MnxO1+x catalyst shows good activity as well as good stability compared to the commercial Pt/C based catalyst. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
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Open AccessCommunication Photohydrogenation of Acetophenone Using Coumarin Dye-Sensitized Titanium Dioxide under Visible Light Irradiation
Catalysts 2015, 5(3), 1417-1424; doi:10.3390/catal5031417
Received: 13 June 2015 / Revised: 27 July 2015 / Accepted: 28 July 2015 / Published: 4 August 2015
Cited by 2 | PDF Full-text (1140 KB) | HTML Full-text | XML Full-text
Abstract
The use of coumarin dyes adsorbed on titanium dioxide (TiO2, P25) successfully extended the photocatalytic UV response of TiO2 toward visible light region. The hydrogenation of acetophenone (AP) using TiO2 modified with coumarin dyes proceeded with good chemical efficiencies
[...] Read more.
The use of coumarin dyes adsorbed on titanium dioxide (TiO2, P25) successfully extended the photocatalytic UV response of TiO2 toward visible light region. The hydrogenation of acetophenone (AP) using TiO2 modified with coumarin dyes proceeded with good chemical efficiencies under visible light irradiation. The role of sacrificial reagents on this dye-sensitized system is also reported. Full article
Open AccessArticle Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone
Catalysts 2015, 5(3), 1425-1444; doi:10.3390/catal5031425
Received: 9 July 2015 / Revised: 27 July 2015 / Accepted: 31 July 2015 / Published: 11 August 2015
Cited by 4 | PDF Full-text (837 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C10H7)C5H3N [Ar = 2,6-i-Pr2C6H3 (L1dipp), 2,4,6-i-Pr3C6H2 (L1tripp), 4-Br-2,6-i-Pr2C
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Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C10H7)C5H3N [Ar = 2,6-i-Pr2C6H3 (L1dipp), 2,4,6-i-Pr3C6H2 (L1tripp), 4-Br-2,6-i-Pr2C6H2 (L1Brdipp)], differing only in the electronic properties of the N-aryl group, have been prepared in high yield by the condensation reaction of 2-{CMe=O}-6-(1-C10H7)C5H3N with the corresponding aniline. Treatment of L1dipp, L1tripp and L1Brdipp with two equivalents of AlMe3 at elevated temperature affords the distorted tetrahedral 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe2N(Ar)}-6-(1-C10H7)C5H3N]AlMe2 [Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-i-Pr3C6H2 (1b), 4-Br-2,6-i-Pr2C6H2 (1c)], in good yield. The X-ray structures of 1a1c reveal that complexation has resulted in concomitant C–C bond formation via methyl migration from aluminum to the corresponding imino carbon in L1aryl; in solution, the restricted rotation of the pendant naphthyl group in 1 confers inequivalent methyl ligand environments. The ring opening polymerization of ε-caprolactone employing 1, in the presence of benzyl alcohol, proceeded efficiently at 30 °C producing polymers of narrow molecular weight distribution with the catalytic activities dependent on the nature of the substituent located at the 4-position of the N-aryl group with the most electron donating i-Pr derivative exhibiting the highest activity (1b > 1a > 1c); at 50 °C 1b mediates 100% conversion of the monomer to polycaprolactone (poly(CL)) in one hour. In addition to 1a, 1b and 1c, the single crystal X-ray structures are reported for L1dipp and L1tripp. Full article
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization and ROP 2015)
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Open AccessArticle Removal of Toluene over NaX Zeolite Exchanged with Cu2+
Catalysts 2015, 5(3), 1479-1497; doi:10.3390/catal5031479
Received: 26 June 2015 / Revised: 20 July 2015 / Accepted: 24 July 2015 / Published: 2 September 2015
Cited by 16 | PDF Full-text (523 KB) | HTML Full-text | XML Full-text
Abstract
Toluene is a major air pollutant emitted from painting and metal coating processes and might have some health effects. Adsorption and catalytic complete oxidation are promising ways to retain or convert toluene into harmless products. The present work aims to develop a bifunctional
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Toluene is a major air pollutant emitted from painting and metal coating processes and might have some health effects. Adsorption and catalytic complete oxidation are promising ways to retain or convert toluene into harmless products. The present work aims to develop a bifunctional material which can be used as an adsorbent and catalyst for low-temperature toluene removal. Copper zeolites were obtained by exchanging the sodium in the parent NaX zeolite with copper from aqueous solutions of Cu(NO3)2∙2.5H2O. Several characterization techniques, H2-TPR, XPS, XRD and N2 physisorption, were used in order to evaluate the redox, surface, structural and textural properties of the materials, respectively. The various materials were tested in adsorption and catalytic processes. The sample with low copper content (1 wt. %) exhibited promising features in terms of toluene adsorption capacity and total oxidation. The results can be correlated to the presence of micropores and well-dispersed CuO species. Full article
Open AccessArticle TiO2-Impregnated Porous Silica Tube and Its Application for Compact Air- and Water-Purification Units
Catalysts 2015, 5(3), 1498-1506; doi:10.3390/catal5031498
Received: 24 June 2015 / Revised: 31 July 2015 / Accepted: 19 August 2015 / Published: 2 September 2015
Cited by 5 | PDF Full-text (618 KB) | HTML Full-text | XML Full-text
Abstract
A simple, convenient, reusable, and inexpensive air- and water-purification unit including a one-end sealed porous amorphous-silica (a-silica) tube coated with TiO2 photocatalyst layers has been developed. The porous a-silica layers were formed through outside vapor deposition (OVD). TiO2 photocatalyst layers were formed through
[...] Read more.
A simple, convenient, reusable, and inexpensive air- and water-purification unit including a one-end sealed porous amorphous-silica (a-silica) tube coated with TiO2 photocatalyst layers has been developed. The porous a-silica layers were formed through outside vapor deposition (OVD). TiO2 photocatalyst layers were formed through impregnation and calcination onto a-silica layers. The resulting porous TiO2-impregnated a-silica tubes were evaluated for air-purification capacity using an acetaldehyde gas decomposition test. The tube (8.5 mm e.d. × 150 mm) demonstrated a 93% removal rate for high concentrations (ca. 300 ppm) of acetaldehyde gas at a single-pass condition with a 250 mL/min flow rate under UV irradiation. The tube also demonstrated a water purification capacity at a rate 2.0 times higher than a-silica tube without TiO2 impregnation. Therefore, the tubes have a great potential for developing compact and in-line VOC removal and water-purification units. Full article
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Open AccessArticle Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst
Catalysts 2015, 5(3), 1535-1553; doi:10.3390/catal5031535
Received: 8 July 2015 / Revised: 25 August 2015 / Accepted: 28 August 2015 / Published: 4 September 2015
Cited by 3 | PDF Full-text (834 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literature, mainly because of its high potential to remediate the pollution of diesel exhaust gases. The implementation of the NH3-SCR process into passenger cars
[...] Read more.
The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literature, mainly because of its high potential to remediate the pollution of diesel exhaust gases. The implementation of the NH3-SCR process into passenger cars requires the use of an ammonia precursor, provided by a urea aqueous solution in the conventional process. Although the thermal decomposition and hydrolysis mechanisms of urea are well documented in the literature, the influence of the direct use of urea on the NOx reduction over SCR catalysts may be problematic. With the aim to evaluate prototype powdered catalysts, a specific synthetic gas bench adjusted to powdered material was developed, allowing the use of NH3 or urea as reductant for direct comparison. The design of the experimental setup allows vaporization of liquid urea at 200 °C under 10 bar using an HPLC pump and a micro injector of 50 μm diameter. This work presents the experimental setup of the catalytic test and some remarkable catalytic results towards further development of new catalytic formulations specifically dedicated to urea-SCR. Indeed, a possible divergence in terms of DeNOx efficiency is evidenced depending on the nature of the reductant, NH3 or urea solution. Particularly, the evaluated catalyst may not allow an optimal NOx conversion because of a lack in ammonia availability when the urea residence time is shortened. This is attributed to insufficient activity of isocyanic acid (HNCO) hydrolysis, which can be improved by addition upstream of an active solid for the hydrolysis reaction such as ZrO2. Thus, this µ-scale synthetic gas bench adjusted to powdered materials enables the specific behaviour of urea use for NOx reduction to be demonstrated. Full article
(This article belongs to the Special Issue Automotive Emission Control Catalysts)
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Open AccessArticle Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene
Catalysts 2015, 5(3), 1554-1573; doi:10.3390/catal5031554
Received: 20 July 2015 / Accepted: 25 August 2015 / Published: 10 September 2015
Cited by 10 | PDF Full-text (962 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A series of bismuth molybdate catalysts with relatively high surface area was prepared via mild hydrothermal synthesis. Variation of the pH value and Bi/Mo ratio during the synthesis allowed tuning of the crystalline Bi-Mo oxide phases, as determined by X-ray diffraction (XRD) and
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A series of bismuth molybdate catalysts with relatively high surface area was prepared via mild hydrothermal synthesis. Variation of the pH value and Bi/Mo ratio during the synthesis allowed tuning of the crystalline Bi-Mo oxide phases, as determined by X-ray diffraction (XRD) and Raman spectroscopy. The pH value during synthesis had a strong influence on the catalytic performance. Synthesis using a Bi/Mo ratio of 1/1 at pH ≥ 6 resulted in γ-Bi2MoO6, which exhibited a better catalytic performance than phase mixtures obtained at lower pH values. However, a significantly lower catalytic activity was observed at pH = 9 due to the low specific surface area. γ-Bi2MoO6 synthesized with Bi/Mo = 1/1 at pH = 6 and 7 exhibited relatively high surface areas and the best catalytic performance. All samples prepared with Bi/Mo = 1/1, except samples synthesized at pH = 1 and 9, showed better catalytic performance than samples synthesized with Bi/Mo = 2/3 at pH = 4 and 9 and γ-Bi2MoO6 synthesized by co-precipitation at pH = 7. At temperatures above 440 °C, the catalytic activity of the hydrothermally synthesized bismuth molybdates started to decrease due to sintering and loss of surface area. These results support that a combination of the required bismuth molybdate phase and a high specific surface area is crucial for a good performance in the selective oxidation of propylene. Full article
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Open AccessArticle Investigation of Room Temperature Synthesis of Titanium Dioxide Nanoclusters Dispersed on Cubic MCM-48 Mesoporous Materials
Catalysts 2015, 5(3), 1603-1621; doi:10.3390/catal5031603
Received: 2 August 2015 / Revised: 1 September 2015 / Accepted: 11 September 2015 / Published: 18 September 2015
Cited by 3 | PDF Full-text (389 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Titania containing cubic MCM-48 mesoporous materials were synthesized successfully at room temperature by a modified Stöber method. The integrity of the cubic mesoporous phase was retained even at relatively high loadings of titania. The TiO2-MCM-48 materials were extensively characterized by a
[...] Read more.
Titania containing cubic MCM-48 mesoporous materials were synthesized successfully at room temperature by a modified Stöber method. The integrity of the cubic mesoporous phase was retained even at relatively high loadings of titania. The TiO2-MCM-48 materials were extensively characterized by a variety of physico-chemical techniques. The physico-chemical characterization indicate that Ti4+ ions can be substituted in framework tetrahedral positions. The relative amount of Ti4+ ions in tetrahedral position was dependent on the order of addition of the precursor. Even at relatively high loadings of titania, no distinct bulk phase of titania could be observed indicating that the titania nanoclusters are well dispersed on the high surface area mesoporous material and probably exist as amorphous nanoclusters. The TiO2-MCM-48 materials were found to exhibit 100% selectivity in the cyclohexene oxidation at room temperature in the presence of tert-butylhydroperoxide (t-BHP) as the oxidant. The results suggest that room temperature synthesis is an attractive option for the preparation of TiO2-MCM-48 materials with interesting catalytic properties. Full article
Open AccessArticle Electrocatalytic Activity and Durability of Pt-Decorated Non-Covalently Functionalized Graphitic Structures
Catalysts 2015, 5(3), 1622-1635; doi:10.3390/catal5031622
Received: 26 May 2015 / Revised: 7 September 2015 / Accepted: 11 September 2015 / Published: 21 September 2015
Cited by 5 | PDF Full-text (1270 KB) | HTML Full-text | XML Full-text
Abstract
Carbon graphitic structures that differ in morphology, graphiticity and specific surface area were used as support for platinum for Oxygen Reduction Reaction (ORR) in low temperature fuel cells. Graphitic supports were first non-covalently functionalized with pyrene carboxylic acid (PCA) and, subsequently, platinum nanoparticles
[...] Read more.
Carbon graphitic structures that differ in morphology, graphiticity and specific surface area were used as support for platinum for Oxygen Reduction Reaction (ORR) in low temperature fuel cells. Graphitic supports were first non-covalently functionalized with pyrene carboxylic acid (PCA) and, subsequently, platinum nanoparticles were nucleated on the surface following procedures found in previous studies. Non-covalent functionalization has been proven to be advantageous because it allows for a better control of particle size and monodispersity, it prevents particle agglomeration since particles are bonded to the surface, and it does not affect the chemical and physical resistance of the support. Synthesized electrocatalysts were characterized by electrochemical half-cell studies, in order to evaluate the Electrochemically Active Surface Area (ECSA), ORR activity, and durability to potential cycling and corrosion resistance. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
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Review

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Open AccessReview Utilization of Volatile Organic Compounds as an Alternative for Destructive Abatement
Catalysts 2015, 5(3), 1092-1151; doi:10.3390/catal5031092
Received: 7 March 2015 / Revised: 17 June 2015 / Accepted: 24 June 2015 / Published: 1 July 2015
Cited by 5 | PDF Full-text (862 KB) | HTML Full-text | XML Full-text
Abstract
The treatment of volatile organic compounds (VOC) emissions is a necessity of today. The catalytic treatment has already proven to be environmentally and economically sound technology for the total oxidation of the VOCs. However, in certain cases, it may also become economical to
[...] Read more.
The treatment of volatile organic compounds (VOC) emissions is a necessity of today. The catalytic treatment has already proven to be environmentally and economically sound technology for the total oxidation of the VOCs. However, in certain cases, it may also become economical to utilize these emissions in some profitable way. Currently, the most common way to utilize the VOC emissions is their use in energy production. However, interesting possibilities are arising from the usage of VOCs in hydrogen and syngas production. Production of chemicals from VOC emissions is still mainly at the research stage. However, few commercial examples exist. This review will summarize the commercially existing VOC utilization possibilities, present the utilization applications that are in the research stage and introduce some novel ideas related to the catalytic utilization possibilities of the VOC emissions. In general, there exist a vast number of possibilities for VOC utilization via different catalytic processes, which creates also a good research potential for the future. Full article
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Open AccessReview Recent Progress on Fe/N/C Electrocatalysts for the Oxygen Reduction Reaction in Fuel Cells
Catalysts 2015, 5(3), 1167-1192; doi:10.3390/catal5031167
Received: 11 May 2015 / Revised: 21 June 2015 / Accepted: 23 June 2015 / Published: 6 July 2015
Cited by 20 | PDF Full-text (2013 KB) | HTML Full-text | XML Full-text
Abstract
In order to reduce the overall system cost, the development of inexpensive, high-performance and durable oxygen reduction reaction (ORR)N, Fe-codoped carbon-based (Fe/N/C) electrocatalysts to replace currently used Pt-based catalysts has become one of the major topics in research on fuel cells. This review
[...] Read more.
In order to reduce the overall system cost, the development of inexpensive, high-performance and durable oxygen reduction reaction (ORR)N, Fe-codoped carbon-based (Fe/N/C) electrocatalysts to replace currently used Pt-based catalysts has become one of the major topics in research on fuel cells. This review paper lays the emphasis on introducing the progress made over the recent five years with a detailed discussion of recent work in the area of Fe/N/C electrocatalysts for ORR and the possible Fe-based active sites. Fe-based materials prepared by simple pyrolysis of transition metal salt, carbon support, and nitrogen-rich small molecule or polymeric compound are mainly reviewed due to their low cost, high performance, long stability and because they are the most promising for replacing currently used Pt-based catalysts in the progress of fuel cell commercialization. Additionally, Fe-base catalysts with small amount of Fe or new structure of Fe/Fe3C encased in carbon layers are presented to analyze the effect of loading and existence form of Fe on the ORR catalytic activity in Fe-base catalyst. The proposed catalytically Fe-centered active sites and reaction mechanisms from various authors are also discussed in detail, which may be useful for the rational design of high-performance, inexpensive, and practical Fe-base ORR catalysts in future development of fuel cells. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessReview Recent Development of Pd-Based Electrocatalysts for Proton Exchange Membrane Fuel Cells
Catalysts 2015, 5(3), 1221-1274; doi:10.3390/catal5031221
Received: 7 May 2015 / Revised: 2 July 2015 / Accepted: 6 July 2015 / Published: 15 July 2015
Cited by 19 | PDF Full-text (1937 KB) | HTML Full-text | XML Full-text
Abstract
This review selectively summarizes the latest developments in the Pd-based cataysts for low temperature proton exchange membrane fuel cells, especially in the application of formic acid oxidation, alcohol oxidation and oxygen reduction reaction. The advantages and shortcomings of the Pd-based catalysts for electrocatalysis
[...] Read more.
This review selectively summarizes the latest developments in the Pd-based cataysts for low temperature proton exchange membrane fuel cells, especially in the application of formic acid oxidation, alcohol oxidation and oxygen reduction reaction. The advantages and shortcomings of the Pd-based catalysts for electrocatalysis are analyzed. The influence of the structure and morphology of the Pd materials on the performance of the Pd-based catalysts were described. Finally, the perspectives of future trends on Pd-based catalysts for different applications were considered. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessReview Advances in Ceramic Supports for Polymer Electrolyte Fuel Cells
Catalysts 2015, 5(3), 1445-1464; doi:10.3390/catal5031445
Received: 29 June 2015 / Revised: 2 August 2015 / Accepted: 6 August 2015 / Published: 17 August 2015
Cited by 11 | PDF Full-text (897 KB) | HTML Full-text | XML Full-text
Abstract
Durability of catalyst supports is a technical barrier for both stationary and transportation applications of polymer-electrolyte-membrane fuel cells. New classes of non-carbon-based materials were developed in order to overcome the current limitations of the state-of-the-art carbon supports. Some of these materials are designed
[...] Read more.
Durability of catalyst supports is a technical barrier for both stationary and transportation applications of polymer-electrolyte-membrane fuel cells. New classes of non-carbon-based materials were developed in order to overcome the current limitations of the state-of-the-art carbon supports. Some of these materials are designed and tested to exceed the US DOE lifetime goals of 5000 or 40,000 hrs for transportation and stationary applications, respectively. In addition to their increased durability, the interactions between some new support materials and metal catalysts such as Pt result in increased catalyst activity. In this review, we will cover the latest studies conducted with ceramic supports based on carbides, oxides, nitrides, borides, and some composite materials. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessReview Nanoscale Alloying in Electrocatalysts
Catalysts 2015, 5(3), 1465-1478; doi:10.3390/catal5031465
Received: 16 May 2015 / Revised: 23 July 2015 / Accepted: 5 August 2015 / Published: 19 August 2015
Cited by 2 | PDF Full-text (3896 KB) | HTML Full-text | XML Full-text
Abstract
In electrochemical energy conversion and storage, existing catalysts often contain a high percentage of noble metals such as Pt and Pd. In order to develop low-cost electrocatalysts, one of the effective strategies involves alloying noble metals with other transition metals. This strategy promises
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In electrochemical energy conversion and storage, existing catalysts often contain a high percentage of noble metals such as Pt and Pd. In order to develop low-cost electrocatalysts, one of the effective strategies involves alloying noble metals with other transition metals. This strategy promises not only significant reduction of noble metals but also the tunability for enhanced catalytic activity and stability in comparison with conventional catalysts. In this report, some of the recent approaches to developing alloy catalysts for electrocatalytic oxygen reduction reaction in fuel cells will be highlighted. Selected examples will be also discussed to highlight insights into the structural and electrocatalytic properties of nanoalloy catalysts, which have implications for the design of low-cost, active, and durable catalysts for electrochemical energy production and conversion reactions. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
Open AccessReview Recent Advances on Electro-Oxidation of Ethanol on Pt- and Pd-Based Catalysts: From Reaction Mechanisms to Catalytic Materials
Catalysts 2015, 5(3), 1507-1534; doi:10.3390/catal5031507
Received: 8 June 2015 / Revised: 13 August 2015 / Accepted: 13 August 2015 / Published: 2 September 2015
Cited by 53 | PDF Full-text (1421 KB) | HTML Full-text | XML Full-text
Abstract
The ethanol oxidation reaction (EOR) has drawn increasing interest in electrocatalysis and fuel cells by considering that ethanol as a biomass fuel has advantages of low toxicity, renewability, and a high theoretical energy density compared to methanol. Since EOR is a complex multiple-electron
[...] Read more.
The ethanol oxidation reaction (EOR) has drawn increasing interest in electrocatalysis and fuel cells by considering that ethanol as a biomass fuel has advantages of low toxicity, renewability, and a high theoretical energy density compared to methanol. Since EOR is a complex multiple-electron process involving various intermediates and products, the mechanistic investigation as well as the rational design of electrocatalysts are challenging yet essential for the desired complete oxidation to CO2. This mini review is aimed at presenting an overview of the advances in the study of reaction mechanisms and electrocatalytic materials for EOR over the past two decades with a focus on Pt- and Pd-based catalysts. We start with discussion on the mechanistic understanding of EOR on Pt and Pd surfaces using selected publications as examples. Consensuses from the mechanistic studies are that sufficient active surface sites to facilitate the cleavage of the C–C bond and the adsorption of water or its residue are critical for obtaining a higher electro-oxidation activity. We then show how this understanding has been applied to achieve improved performance on various Pt- and Pd-based catalysts through optimizing electronic and bifunctional effects, as well as by tuning their surface composition and structure. Finally we point out the remaining key problems in the development of anode electrocatalysts for EOR. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
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Open AccessReview Nitrogen-Doped Carbon Nanotube and Graphene Materials for Oxygen Reduction Reactions
Catalysts 2015, 5(3), 1574-1602; doi:10.3390/catal5031574
Received: 28 May 2015 / Revised: 13 August 2015 / Accepted: 1 September 2015 / Published: 14 September 2015
Cited by 45 | PDF Full-text (2034 KB) | HTML Full-text | XML Full-text
Abstract
Nitrogen-doped carbon materials, including nitrogen-doped carbon nanotubes (NCNTs) and nitrogen-doped graphene (NG), have attracted increasing attention for oxygen reduction reaction (ORR) in metal-air batteries and fuel cell applications, due to their optimal properties including excellent electronic conductivity, 4e transfer and superb mechanical
[...] Read more.
Nitrogen-doped carbon materials, including nitrogen-doped carbon nanotubes (NCNTs) and nitrogen-doped graphene (NG), have attracted increasing attention for oxygen reduction reaction (ORR) in metal-air batteries and fuel cell applications, due to their optimal properties including excellent electronic conductivity, 4e transfer and superb mechanical properties. Here, the recent progress of NCNTs- and NG-based catalysts for ORR is reviewed. Firstly, the general preparation routes of these two N-doped carbon-allotropes are introduced briefly, and then a special emphasis is placed on the developments of both NCNTs and NG as promising metal-free catalysts and/or catalyst support materials for ORR. All these efficient ORR electrocatalysts feature a low cost, high durability and excellent performance, and are thus the key factors in accelerating the widespread commercialization of metal-air battery and fuel cell technologies. Full article
(This article belongs to the Special Issue Electrocatalysis in Fuel Cells) Printed Edition available
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