Time filter

Source Type

Figueiredo J.L.,Laboratorio Of Catalise E Materiais Lcm | Pereira M.F.R.,Laboratorio Of Catalise E Materiais Lcm
Catalysis Today | Year: 2010

In addition to its use as a catalyst support, carbon can find application as a catalyst on its own, and a large number of applications of carbon as a catalyst, both in the liquid and in the gas phase, have been reported. Oxygen and nitrogen functional groups can perform as active sites, chemisorbing the reactants and forming surface intermediates of adequate strength. The role of surface chemistry in carbon catalysis is reviewed, with particular emphasis on those cases where the active sites have been properly identified, and useful activity correlations established. © 2009 Elsevier B.V. All rights reserved.

Machado B.F.,Laboratorio Of Catalise E Materiais Lcm | Gomes H.T.,Laboratorio Of Catalise E Materiais Lcm | Gomes H.T.,Polytechnic Institute of Bragança | Serp P.,CNRS Coordination Chemistry | And 3 more authors.
Catalysis Today | Year: 2010

Carbon xerogels are mesoporous materials obtained upon pyrolysis of the dried gels resulting from polycondensation of resorcinol and formaldehyde. Treatment with nitric acid under severe conditions introduces high amounts of oxygen containing functional groups onto the surface of the material, leading however to the collapse of its porous structure. The resulting material is then used to support 1 wt.% Pt, Ir and Ru monometallic catalysts by wet impregnation using organometallic precursors. The catalysts are characterized by N2 adsorption-desorption isotherms at 77 K, temperature programmed desorption coupled with mass spectrometry, scanning and transmission electron microscopy, and H2 chemisorption. The liquid-phase selective hydrogenation of cinnamaldehyde to cinnamyl alcohol is used in order to assess the catalytic performance of the prepared materials. Pt and Ru catalysts are initially very selective towards the hydrogenation of the olefinic double bond, while Ir is mostly selective towards the carbonyl group. After a thermal post-reduction treatment at 973 K, selectivity towards cinnamyl alcohol is significantly improved regardless of the metal nature. The Pt catalyst exhibits the best behavior, a complete shift in C=C to C=O hydrogenation being detected. The improvement in selectivity is rationalized in terms of both an increase in metal particle size and a modification in the surface chemistry of the catalyst after the post-reduction treatment. © 2009 Elsevier B.V. All rights reserved.

Carabineiro S.A.C.,Laboratorio Of Catalise E Materiais Lcm | Bastos S.S.T.,Laboratorio Of Catalise E Materiais Lcm | Orfao J.J.M.,Laboratorio Of Catalise E Materiais Lcm | Pereira M.F.R.,Laboratorio Of Catalise E Materiais Lcm | And 2 more authors.
Applied Catalysis A: General | Year: 2010

Cerium oxides were synthesized by an exotemplating procedure using both activated carbon and carbon xerogel as templates. The template effect and the preparation method were investigated. The surface area of the materials varied from 73 to 114 m2 g-1, being similar to samples prepared by standard precipitation and calcination techniques (150 and 98 m2 g-1, respectively), but much larger than a commercial ceria sample (20 m2 g-1), used for comparison purposes. Samples prepared using xerogel as template have, approximately, twice as much porosity than those prepared with activated carbon, and the mesopores of the first are roughly 4 times larger than those of the latter. Cerianite CeO2 was the only phase detected by XRD for all materials. Gold was loaded onto these materials by a double impregnation method. The catalytic performance of these ceria oxide materials alone and loaded with gold was tested in the oxidation of carbon monoxide. Xerogel prepared samples showed to be the most active in CO oxidation. Addition of Au increased the activity up to two orders of magnitude, at room temperature. With the unloaded samples, complete conversion was only achieved above 400 °C, but when Au was loaded, full CO conversion occurred already at 75 °C. Analysis of selected samples by HAADF and HRTEM showed that the gold particle size was 5-10 nm for the most active sample, and 8-13 nm for the least active. H2-TPR experiments proved that addition of gold significantly helped to improve the reducibility of the surface oxygen on CeO2. Both for ceria and Au/ceria materials, it was observed that the temperature at which the CO conversion started is related to the temperature of the first peak of the TPR spectrum, showing that the activity depends on the availability of surface oxygen. Experiments without oxygen in the feed, in the presence of ceria catalysts, suggest that the lattice oxygen can react with CO. It is shown that there is a significant correlation between the catalytic activity and the lattice oxygen donating ability. The TPR results suggest that gold is in its reduced state in the "fresh" Au/ceria samples. © 2010 Elsevier B.V. All rights reserved.

Mezohegyi G.,Rovira i Virgili University | Goncalves F.,Laboratorio Of Catalise E Materiais Lcm | Orfao J.J.M.,Laboratorio Of Catalise E Materiais Lcm | Fabregat A.,Rovira i Virgili University | And 4 more authors.
Applied Catalysis B: Environmental | Year: 2010

Anaerobic reduction of two textile azo dyes (Orange II and Reactive Black 5) was investigated in upflow stirred packed-bed reactors (USPBRs) with biological activated carbon (BAC) system. The bioreactors were prepared with tailored activated carbons (ACs) having different textural properties and various surface chemistries. A kinetic model proposed previously was able to describe the catalytic azo reduction in all cases. Decolourisation with very high reduction rates took place in the case of each AC. Best dye removals were ensured by the AC having the highest surface area: conversion values above 88% were achieved in the case of both azo dyes at a space time of 0.23 min or higher, corresponding to a very short hydraulic residence time of about 0.30 min at the most. The decolourisation rates were found to be significantly influenced by the textural properties of AC and moderately affected by its surface chemistry. The results confirmed the catalytic effects of carbonyl/quinone sites and, in addition, delocalized π-electrons seemed to play a role in the catalytic reduction in the absence of surface oxygen groups. © 2009 Elsevier B.V. All rights reserved.

Loading Laboratorio Of Catalise E Materiais Lcm collaborators
Loading Laboratorio Of Catalise E Materiais Lcm collaborators