Showing papers by "José J.M. Órfão published in 2011"
TL;DR: Cerium oxides prepared by the precipitation method and hydrothermal synthesis, with distinct morphologies and particle size, were tested as catalysts in the ozonation of selected organic compounds.
Abstract: Cerium oxides prepared by the precipitation method and hydrothermal synthesis, with distinct morphologies and particle size, were tested as catalysts in the ozonation of selected organic compounds. Oxalic acid, aniline and a reactive dye were used as representative of organic pollutants. In the case of oxalic acid, an increase in the catalytic activity with the increase of the percentage of Ce(III) on the surface was observed. Both single and catalytic ozonation allowed the total removal of aniline after 30 min of reaction; the cerium oxide prepared by the precipitation method was the best catalyst for promoting the mineralization of aniline solutions. TOC removals close to 100% were obtained in all cases when cerium oxides were used as catalysts in the ozonation of the reactive dye tested.
109 citations
TL;DR: In this article, a set of modified activated carbons with different levels of oxygenated functional groups on the surface, but with no major differences in their textural parameters, was prepared, and a strong effect of the activated carbon surface chemistry on the catalytic activity was observed.
100 citations
TL;DR: In this paper, the influence of support in the performance of Pd monometallic and Pd-Cu bimetallic catalysts for the reduction of nitrate in water was investigated.
84 citations
TL;DR: In this article, the results were compared with those obtained in non-catalytic ozonation and catalytic catalysed by cerium oxide and carbon materials (activated carbon, carbon xerogel).
Abstract: Cerium oxide–carbon composites were prepared and tested as ozonation catalysts for the removal of two selected carboxylic acids, oxalic and oxamic, and one textile dye (C.I. Reactive Blue 5). The results were compared with those obtained in non-catalytic ozonation and ozonation catalysed by cerium oxide and carbon materials (activated carbon, carbon xerogel). With the exception of cerium oxide, a total degradation of oxalic acid was obtained in approximately 90 min for all prepared catalysts and the catalytic activity increases with the amount of carbon present in the composites. Despite of oxamic acid be more refractory to ozonation than oxalic acid, 75% of oxamic acid removal was achieved after 10 h of reaction in the presence of the ceria-activated carbon composite with 90% of carbon material. In the mineralization of the textile dye, the catalytic activity of the composites increases with the amount of activated carbon introduced.
68 citations
TL;DR: In this article, the use of multi-walled carbon nanotubes as support for Au nanoparticles results in the preferential chemoselective orientation of glycerol oxidation towards the reaction of the secondary alcohol function; a dihydroxyacetone selectivity of 60% was obtained in combination with a high activity.
63 citations
TL;DR: In this article, several physical mixtures with mono and bimetallic catalysts were tested in the catalytic nitrate reduction with hydrogen, and it was observed that the physical mixture of Pd and Cu or Pt and Cu monometric catalysts are similar or more active than the corresponding bimetRIC catalysts.
Abstract: Several physical mixtures with mono and bimetallic catalysts were tested in the catalytic nitrate reduction with hydrogen. It was observed that the physical mixtures of Pd and Cu or Pt and Cu monometallic catalysts are similar or more active than the corresponding bimetallic catalysts. The mixtures with Pd catalysts are the most selective to nitrogen, being the mixtures with Rh catalysts the most selective to ammonium. The addition of a monometallic catalyst to a bimetallic catalyst does not decrease the accumulation of nitrite in solution neither the formation of ammonium. The activity of the mixture of monometallic catalysts is due to the formation of in situ bimetallic catalysts as a result of the adsorption of the leached copper. The noble metal must be already supported, and copper does not need to be in the metallic form.
60 citations
TL;DR: The surface chemistry of activated carbon plays a key role in the performance of catalysts for glycerol oxidization as mentioned in this paper, and Rhodium is a highly efficient catalyst when the support has neutral or basic properties.
Abstract: Noble metal catalysts (Pt, Ir, Pd, Rh, Au) supported on activated carbon were assessed for glycerol oxidation. Rhodium is a highly efficient catalyst when the support has neutral or basic properties. The surface chemistry of activated carbon plays a key role in the performance.
53 citations
TL;DR: In this paper, two types of high surface area carbon adsorbents were prepared, namely a carbon xerogel and a templated carbon, and both materials were subsequently subjected to appropriate treatments in order to modify their surface chemistries, while keeping their textural properties relatively unchanged.
Abstract: The removal of textile dyes by adsorption onto carbon materials with extended mesoporosity is addressed in the present work. Two types of high surface area carbon adsorbents were prepared, namely a carbon xerogel and a templated carbon. Both materials were subsequently subjected to appropriate treatments in order to modify their surface chemistries, while keeping their textural properties relatively unchanged. The carbon adsorbents were extensively characterized by different techniques in order to correlate their adsorption performances with the corresponding surface properties. The behavior of the different materials was evaluated by determining equilibrium adsorption isotherms of two anionic dyes (Reactive Red 241 and Acid Blue 113) at different pH values. The results are compared with data previously obtained with commercial activated carbons subjected to the same treatments, and discussed in terms of the carbon surface chemistry and the interaction between the dye molecules and the adsorbent surface (dispersive and electrostatic interactions).
51 citations
TL;DR: The catalytic oxidation of two-component VOC mixtures (ethanol, ethyl acetate and toluene) was studied over cryptomelane and remarkable mixture effects were observed on the activity and the selectivity.
39 citations