Palladium and platinum catalysts supported on carbon nanofiber coated monoliths for low-temperature combustion of BTX
ABSTRACT In this work carbon nanofiber (CNF)-coated monoliths with a very thin, homogeneous, consistent and good adhered CNF layer were obtained by means of catalytic decomposition of ethylene on Ni particles.The catalytic behaviour of Pt and Pd supported on the CNF-coated monoliths was studied in the low-temperature catalytic combustion of benzene, toluene and m-xylene (BTX) and compared with the performance of Pt and Pd supported on γ-Al2O3 coated monoliths.The catalysts supported on CNF-coated monoliths were the most active, independent of the metal catalyst or the type of the tested aromatic compound. TPD experiments showed that the γ-Al2O3 phase retained important amounts of the water molecules produced during the reaction. When water vapour was supplied to the reactant flow, the activity of Pd catalysts decreased much stronger than the Pt ones, and the activity of the Pt catalysts supported on the γ-Al2O3 was more affected than that of the catalysts supported on CNF.BTX combustion reactions seem to be catalyzed by Pt and Pd through different kinetic mechanisms, explaining why Pt catalysts always were more active than the Pd ones deposited on the same type of support. Pd catalyzed combustion of benzene is strongly inhibited by oxygen and by water.Catalysts supported on CNF-coated monoliths showed a selectivity to burn benzene better than toluene or m-xylene, attributed to a better aromatic-CNF surface interaction.
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ABSTRACT: The specific adsorption of oxygenated and aliphatic gasoline components onto activated carbons (ACs) was studied under static and dynamic conditions. Ethanol and n-octane were selected as target molecules. A highly porous activated carbon (CA) was prepared by means of two processes: carbonization and chemical activation of olive stone residues. Different types of oxygenated groups, identified and quantified by TPD and XPS, were generated on the CA surface using an oxidation treatment with ammonium peroxydisulfate and then selectively removed by thermal treatments, as confirmed by TPD results. Chemical and porous transformations were carefully analyzed throughout these processes and related to their VOC removal performance. The analysis of the adsorption process under static conditions and the thermal desorption of VOCs enabled us to determine the total adsorption capacity and regeneration possibilities. Breakthrough curves obtained for the adsorption process carried out under dynamic conditions provided information about the mass transfer zone in each adsorption bed. While n-octane adsorption is mainly determined by the porosity of activated carbons, ethanol adsorption is related to their surface chemistry, and in particular is enhanced by the presence of carboxylic acid groups.Journal of hazardous materials 10/2013; 263. DOI:10.1016/j.jhazmat.2013.10.012 · 4.33 Impact Factor
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ABSTRACT: Mesoporous activated carbons were obtained by chemical activation of kraft lignin with H3PO4 and used as supports for the preparation of carbon-based Pd catalysts with low palladium content (0.5%). The catalytic properties of the carbon-based Pd samples were evaluated in the catalytic oxidation of toluene. The effect that a thermal treatment at 900 °C in inert atmosphere carried out before and after the Pd-deposition produced on the structure and activity of the catalysts was analyzed. The catalysts obtained show high external surface areas and mesopore volumes. The chemical activation with H3PO4 yielded carbon supports with a significant amount of surface phosphorus, in form of COPO3, CPO3 and C3PO groups. These phosphorus groups act like physical barrier, increasing the oxidation resistance of the catalysts and avoiding the burn-off of the carbon substrate during the oxidation of the VOCs. TEM analysis confirmed the presence of well-dispersed Pd particles, with sizes between 5 and 12 nm. A kinetic study of the catalytic oxidation of toluene was performed. The reaction seems to proceed through a Langmuir–Hinshelwood mechanism, whose rate-limiting step is the surface reaction between adsorbed toluene and oxygen adsorbed dissociatively, with an activation energy value of 83 kJ mol−1. Toluene and xylene were oxidized to CO2 and H2O in the temperature range of 150–400 °C at a space velocity of 19,000 h−1.Applied Catalysis B Environmental 02/2010; 94(1-2-94):8-18. DOI:10.1016/j.apcatb.2009.10.015 · 6.01 Impact Factor
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ABSTRACT: Honeycomb monoliths consist of a large number of parallel channels that provide high contact efficiencies between the monolith and gas flow streams. These structures are used as adsorbents or supports for catalysts when large gas volumes are treated, because they offer very low pressure drop, short diffusion lengths and no obstruction by particulate matter. Carbon-based honeycomb monoliths can be integral or carbon-coated ceramic monoliths, and they take advantage of the versatility of the surface area, pore texture and surface chemistry of carbon materials. Here, we review the preparation methods of these monoliths, their characteristics and environmental applications.Materials 02/2010; 3(2):1203-1227. DOI:10.3390/ma3021203 · 1.88 Impact Factor