Catalysts2015, 5(3), 1193-1201; doi:10.3390/catal5031193 (registering DOI) - published 6 July 2015 Show/Hide Abstract
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 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.
Catalysts2015, 5(3), 1167-1192; doi:10.3390/catal5031167 (registering DOI) - published 6 July 2015 Show/Hide Abstract
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 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.
Catalysts2015, 5(3), 1152-1166; doi:10.3390/catal5031152 (registering DOI) - published 3 July 2015 Show/Hide Abstract
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 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.
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 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.
Catalysts2015, 5(3), 1079-1091; doi:10.3390/catal5031079 - published 30 June 2015 Show/Hide Abstract
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 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.
Catalysts2015, 5(3), 1068-1078; doi:10.3390/catal5031068 - published 29 June 2015 Show/Hide Abstract
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 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.