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Ribeiro L.S.,Laboratory of Catalysis and Materials LCM | Orfao J.J.M.,Laboratory of Catalysis and Materials LCM | Pereira M.F.R.,Laboratory of Catalysis and Materials LCM
Green Processing and Synthesis | Year: 2015

The catalytic conversion of lignocellulosic biomass to obtain high added value compounds and fuels is a rapidly developing field. Given the abundance of this renewable raw material and its reduced impact on the food chain, it is an attractive source for obtaining chemicals or fuels in the context of a sustainable economy. In this work, bi-functional catalysts were developed that were capable of performing in a single step the hydrolysis and hydrogenation of cellulose to produce compounds that may be used in the production of fine chemicals or easily converted into fuels (e.g., sorbitol). Different activated carbon (AC) supported metal catalysts were examined for the one-pot hydrolytic hydrogenation of cellulose. Among the prepared catalysts, 0.4% Ru/AC was shown to be the most active and selective for the conversion of cellulose into sorbitol. When microcrystalline cellulose was used, a conversion of 32% was reached after 5 h of reaction, with a selectivity to sorbitol of 30%. Moreover, ball-milled cellulose allowed attaining conversions over 50%, with selectivities to sorbitol of 45%. The results obtained showed that Ru/AC is effective for the hydrolytic hydrogenation of cellulose to sugar alcohols and that the conversion can be greatly improved by using the substrate after pre-treatment by ball-milling. © 2015 by De Gruyter 2015.

Gomes H.T.,Laboratory of Catalysis and Materials LCM | Gomes H.T.,Polytechnic Institute of Bragança | Miranda S.M.,Polytechnic Institute of Bragança | Sampaio M.J.,Polytechnic Institute of Bragança | And 2 more authors.
Catalysis Today | Year: 2010

Different liquid phase thermal treatments were applied to a commercial activated carbon (Norit ROX 0.8) in order to produce modified activated carbons with varying surface chemistry and increased acidic character. Chemical characterization of the prepared materials includes determination of the point of zero charge and evaluation of the concentration and nature of acidic and basic surface functionalities by acid/base titrations and temperature programmed desorption. The prepared materials were used as catalysts in the catalytic wet peroxide oxidation of the acid dye Chromotrope 2R in order to assess their removal efficiency. The relationship between the surface chemistry and efficiency for dye removal is discussed. As expected, decreasing acidity of the catalysts surface will correlate with increasing dye conversion. Unexpectedly, treatment with sulphuric acid leads to a very high yield of dye removal which falls out of the previous correlation. This was explained in terms of the introduction of sulphur containing groups on the carbon surface, which promotes the surface interaction between the pollutant and hydrogen peroxide: higher production of hydroxyl radicals close to the pollutant leads to improved dye removal. In addition, reutilization studies show that the catalyst prepared by sulphuric acid treatment is able to keep its performance in successive runs. © 2010 Elsevier B.V. All rights reserved.

Marques R.R.N.,Laboratory of Catalysis and Materials LCM | Machado B.F.,Laboratory of Catalysis and Materials LCM | Faria J.L.,Laboratory of Catalysis and Materials LCM | Silva A.M.T.,Laboratory of Catalysis and Materials LCM
Carbon | Year: 2010

The surface chemistry of Single-Walled Carbon Nanotubes is finely tailored by a HNO3 hydrothermal method. Temperature Programmed Desorption analysis is used to determine the nature and amount of different oxygenated functionalities, which are introduced in a controlled mode. The degree of oxygen functionalization is correlated with HNO3 concentration through a mathematical function. Operating temperature and HNO3 concentration are key parameters in the modification of the surface chemistry, in accordance with previous results obtained with a carbon xerogel subjected to the same hydrothermal treatment. A detailed comparison between the results obtained with both materials indicates that the yield of the HNO3 hydrothermal functionalization strongly depends on the texture of the carbon material that is used. © 2009 Elsevier Ltd. All rights reserved.

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