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The use of porous materials to eliminate volatile organic compounds (VOCs) has proven very effective towards achieving sustainability and environmental protection goals. The activity of zeolites and macro-mesoporous metal-oxide supports in the total oxidation of VOCs has been investigated, with and without noble-metal deposition, to develop highly active catalyst systems where the formation of by-products was minimal. The first catalysts employed were zeolites, which offered a good activity in the oxidation of VOCs, but were rapidly deactivated by coke deposition. The effects of the acido-basicity and ionic exchange of these zeolites showed that a higher basicity was related to exchanged ions with lower electronegativities, resulting in better catalytic performances in the elimination of VOCs. Following on from this work, noble metals were deposited onto macro-mesoporous metal-oxide supports to form mono and bimetallic catalysts. These were then tested in the oxidation of toluene to study their catalytic performance and their deactivation process. PdAu/TiO(2) and PdAu/TiO(2) -ZrO(2) 80/20 catalysts demonstrated the best activity and life span in the oxidation of toluene and propene and offered the lowest temperatures for a 50 % conversion of VOCs and the lowest coke content after catalytic testing. Different characterization techniques were employed to explain the changes occurring in catalyst structure during the oxidation of toluene and propene., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Highlights: [•] Influence of doping of porous titania with metal oxides on the oxidation of VOC. [•] Pd and Au loaded materials as highly active catalysts in the removal of toluene. [•] Catalyst's stability in extreme VOC oxidation conditions. [Copyright &y& Elsevier]

Highlights: [•] Synthesis of hierarchically porous Nb doped TiO2 catalyst support. [•] Preservation of multi-modal porosity on calcination to crystalline anatase phase. [•] Metal oxide–catalyst interaction influenced by chemical composition of support. [•] Nb promotes catalytic destruction of pollutants by noble metal nanoparticles. [•] Increase in activity and CO2 selectivity for Pt/Nb–TiO2 compared to Pt/TiO2. [ABSTRACT FROM AUTHOR]

Abstract: The catalytic properties of palladium and gold nanoparticles deposited on mesoporous TiO2 are investigated in toluene and propene oxidation. The catalysts, containing Pd and Au deposited on mesoporous TiO2 have been prepared by different order of metal deposition (Pd(shell)–Au(core)/TiO2, Pd–Au(alloy)/TiO2 and Au(shell)–Pd(core)/TiO2. For both toluene and propene oxidation reactions, the catalytic activity was found significantly higher when palladium is deposited on already-deposited gold (Pd(shell)–Au(core)/TiO2). This enhanced activity could be explained by the core–shell morphology (Pd–shell and Au-core) observed by UV–vis spectra, TPR profiles and XPS spectra. It was suggested that the oxidation reaction follows a Langmuir–Hinshelwood mechanism where the molecules of oxygen and VOC are in competition for adsorption on the surface of catalyst. Operando DRIFT spectroscopy was carried out to test the catalytic activity in a mixture of volatile organic compounds (toluene and propene). It was demonstrated that there is a competition between the molecules of VOC for adsorption but also the toluene has an inhibition effect for oxidation of propene. [Copyright &y& Elsevier]

Abstract: Cobalt supported on calcined hydrotalcite catalysts were prepared using the memory effect of Mg–Al hydrotalcite. Mg–Al was calcined at different temperatures from 500 to 900°C and dipped in a Co nitrate aqueous solution for surface hydrotalcite regeneration. The calcination at 500°C of the sample Co/Mg–Al(700) leads to an interesting Co mixed oxide supported on calcined hydrotalcite with high specific area and highly active and selective for toluene oxidation. The surface Co hydrotalcite regeneration was observed especially by Infrared Spectroscopy and Scanning Electron Microscopy combined with Energy Dispersive detection of emitted X-ray photons. The reconstruction of the layered structure influences positively the iteraction between cobalt species and the support. [ABSTRACT FROM AUTHOR]