Renaud Cousin

Gold catalysts in environmental remediation and water-gas shift technologies

This review presents studies and investigations of the use of gold catalysts in environmental applications, from the oxidation of CO and volatile organic compounds (VOCs) in environmental technologies to the production of hydrogen, a non-polluting energy source, in the water-gas shift (WGS) reaction. It summarizes a variety of results, from the discovery made by Haruta et al. about the catalytic behaviour of gold in CO oxidation, to the use of gold-based catalysts in environmental remediation, by the catalytic removal of different types of VOC using a wide variety of oxide supports and finally to the use of this highly active noble metal in WGS applications. It also discusses gold loading methods, comparing them in terms of simplicity, efficiency and the resultant particle size and dispersion of Au over various supports. The application of different types of supporting materials is also presented, with a critical discussion of the parameters affecting the choice and use of such materials, i.e. how the support interacts with gold particles and with pollutant molecules along with the advantages a support offers to VOC oxidation and WGS reactions. It ends by highlighting the potential of gold catalyts in the future.

Noble‐Metal‐Based Catalysts Supported on Zeolites and Macro‐Mesoporous Metal Oxide Supports for the Total Oxidation of Volatile Organic Compounds

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.

EPR investigation and reactivity of diesel soot activated (or not) with cerium compounds

Parameters influencing the diesel soot reactivity versus the combustion reaction are studied on two diesel soot samples. The presence of cerium additives favours the reactivity of the doped soot and shifts the combustion reaction towards low temperatures. However, these additives do not affect the CO–CO2 selectivity. Oxygenated and non-oxygenated radicals adsorbed on the carbon particulate are evidenced whatever the composition of the soot sample. After a vacuum treatment, the adsorbed hydrocarbons content drastically decreases and the reactivity of both soot samples is attenuated. However, the cerium-doped sample reveals higher radical contents and also higher reactivity than the non-activated soot. The presence of cerium additives stabilises and strengthens radical–carbon interactions and these hydrocarbon radical species play an important role in the activation of the diesel soot combustion.

Titanium oxide nanotubes as supports of Au or Pd nano-sized catalysts for total oxidation of VOCs

Abstract Titanium oxide nanotubes (TNTs) have been synthesized via laboratory-made TiO2 A and commercial TiO2 P25. 1.5wt% gold or palladium were deposited on TNTA and TNTP25 supports and the catalytic activity was evaluated in propene, methyl ethyl ketone (MEK) and toluene total oxidation. The catalytic properties of supported TNT were correlated with the structural peculiarity and the nature of the TNT, but also with the nature of the noble metal and the kind of the VOC.

Investigation of the elimination of VOC mixtures over a Pd-loaded V-doped TiO2 support

The removal of a butanone–toluene mixture over Pd/5%V-TiO2 and Pd/TiO2 catalysts has been investigated. The V-doped sample showed a higher performance in the oxidation of butanone and also a butanone–toluene mixture, which was attributed to competition between oxygen species and VOCs on vanadium adsorption sites. However in the presence of both VOCs, Pd/5%V-TiO2 showed a higher performance than in the elimination of butanone alone. An operando DRIFT experiment coupled with a mass spectrometer revealed that both VOCs compete in terms of adsorption on the surface of the catalyst. However, toluene adsorption is decreased by MEK, meaning that the latter oxidizes more easily into its by-products, whose combustion causes variations in the surface temperature of the catalyst, thus enhancing the oxidation of toluene molecules present in the gaseous stream.

Effects of the treatment and the mesoporosity of mesostructured TiO2 impregnated with noble metal for VOCs oxidation

Abstract Catalytic oxidation of volatile organic compounds (VOCs) was carried out over catalysts prepared from different nanostructured mesoporous TiO 2 presenting high surface areas and mesoporosity from 2.9 to 10.1 nm. These Pd impregnated solids were found to be powerful catalysts for total oxidation of toluene. However, the pore diameter of 2.9 nm, leading to palladium particles accessible and reducible in the mesopores should explain the interesting catalytic behavior of the Pd/mesoporous TiO 2 sample prepared by CTMABr surfactant and calcined at 400°C.

Usefulness of toxicological validation of VOCs catalytic degradation by air-liquid interface exposure system

Abstract Toluene is one of the most used Volatile Organic Compounds (VOCs) in the industry despite its major health impacts. Catalytic oxidation represents an efficient remediation technique in order to reduce its emission directly at the source, but it can release by‐products. To complete the classical performance assessment using dedicated analytical chemistry methods, we propose to perform an untargeted toxicological validation on two efficient catalysts. Using biological system allows integrating synergy and antagonism in toxic effects of emitted VOCs and by‐products, often described in case of multi‐exposure condition. Catalysts Pd/&agr;‐Al2O3 and Pd/&ggr;‐Al2O3 developed for the oxidation of toluene were both coupled to a Vitrocell® Air‐Liquid Interface (ALI) system, for exposure of human A549 lung cells during 1 h to toluene or to catalysts exhaust before quantification of xenobiotics metabolizing enzymes. This study validated initially the Vitrocell® as an innovative, direct and dynamic model of ALI exposure in the assessment of the performances of new catalysts, showing the presence of chemically undetected by‐products. The comparison of the two catalysts showed then that fewer organic compounds metabolizing genes were induced by Pd/&ggr;‐Al2O3 in comparison to Pd/&agr;‐Al2O3, suggesting that Pd/&ggr;‐Al2O3 is more efficient for toluene total oxidation from a toxicological point of view. Graphical abstract Symbol. No caption available. HighlightsCatalytic oxidation is an efficient remediation technique of industrial VOC emissionsCatalyst performance is generally assessed measuring VOC conversion or CO2 emission, but not the formation of by‐products.Untargeted toxicological validation of catalyst by coupling it to an Air‐Liquid Interface exposure system.Using biological system allows integrating synergy and antagonism in toxic effects of emitted VOCs and by‐products.CYP1A1 induction in exposed A549 cells showed the formation of PAHs undetected by chemical methods.

Catalytic Oxidation of Propylene, Toluene, Carbon Monoxide, and Carbon Black over Au/CeO2 Solids: Comparing the Impregnation and the Deposition-Precipitation Methods

Au/CeO2 solids were prepared by two methods: deposition-precipitation (DP) and impregnation (Imp). The prepared solids were calcined under air at 400°C. Both types of catalysts have been tested in the total oxidation of propylene, toluene, carbon monoxide, and carbon black. Au/CeO2-DP solids were the most reactive owing to the high number of gold nanoparticles and Au+ species and the low concentration of Cl− ions present on its surface compared to those observed in Au/CeO2-Imp solids.

Influence of Shaping on Pd and Pt/TiO2 Catalysts in Total Oxidation of VOCs

The catalytic performance of a commercial TiO2 was investigated towards the total oxidation of toluene. A variety of two titania supports was used in this work, shaped (pellets) and non-shaped (powder) materials. 0.5wt% Pd or Pt were impregnated onto both types of titania supports using the wet impregnation method. A decrease in the surface area of the obtained catalysts was noticed after the catalytic test, although it was still much higher than that of classical titania supports. The catalysts were tested in the total oxidation of toluene, and a major decrease in activity was noticed for Pt impregnated “shaped” supports.

Composition and textural properties of soot and study of their oxidative elimination by catalytic process

Diesel soot and reference carbon black samples have been characterised by analysis of the organic compounds fraction and determination of textural characteristics (specific area). The potential to eliminate such carbonaceous particles has been investigated using a Cu/ZrO2 solid catalyst promoted by potassium additives. The reactivity of soot samples depends on the organic compounds content. In general, Cu-K/ZrO2 catalyst is able to lower significantly the soot oxidation temperature of almost 200°. This high activity is related to the ability of potassium to interact with copper species and to favour the release of active oxygen from the catalyst.