Claude Descorme

Investigation of the oxygen storage process on ceria- and ceria–zirconia-supported catalysts

Abstract A total of 10 noble metal (Rh, Pt, Pd, Ru and Ir) catalysts, either supported on CeO 2 or Ce 0.63 Zr 0.37 O 2 , were prepared. Catalysts were fully characterized using XRD, N 2 adsorption at −196xa0°C, TEM and H 2 chemisorption. Oxygen storage processes were carefully investigated. The influence of temperature was checked and a key role of oxygen diffusion was further demonstrated. A review of the reactions involved in the CO transient oxidation reaction is finally proposed.

Heterogeneous Catalysis: A Key Tool toward Sustainability

The scope of this concept article is to demonstrate through few selected examples taken from recent literature that heterogeneous catalysis is presently an essential tool to achieve a sustainable use of resources for energy, chemical, and material production and to preserve and rehabilitate our environment. Using heterogeneous catalysts for the production of fuels and chemicals reduce the energy demand and minimize the formation of non‐recyclable wastes by increasing the activity and selectivity of fossil and renewable resource conversion. It is now the essential tool for the treatment of pollutants in air and water. The efficiency of photocatalytic processes for the treatment of toxic compounds in air and water is also highlighted. The destruction of pollutants by mineral dust in the atmosphere demonstrates the major role that heterogeneous catalytic processes plays for global environmental preservation.

Palladium-exchanged MFI-type zeolites in the catalytic reduction of nitrogen monoxide by methane. Influence of the Si/Al ratio on the activity and the hydrothermal stability

Abstract Pd-exchanged MFI-type zeolites containing 3.7 and 0.7 framework aluminium atoms per unit cell (corresponding to Si/Al ratios of 25 and 131) were found active in the selective reduction of nitrogen monoxide in the presence of excess oxygen. Upon steaming at 800°C, both catalysts exhibited the total loss of their catalytic activity in the reduction of NO. Such a behaviour was ascribed to the complete aggregation of Pd ions into large metal particles on the external surface of the zeolite crystals. Both supports, although maintaining their crystallinity, are shown to experience extended dealumination upon steaming. Although the loss of Pd exchange capacity could partially explain the Pd migration and sintering, a mechanism involving the formation of mobile Pd hydroxyl entities condensing into PdO particles outside the zeolite crystallites is preferred.

TiO2-supported gold catalysts in the catalytic wet air oxidation of succinic acid: influence of the preparation, the storage and the pre-treatment conditions

Titania-supported gold catalysts were prepared via the so-called deposition–precipitation method, using either urea or ammonia as the precipitation agent and evaluated in the catalytic wet air oxidation of succinic acid (a model pollutant often found in the degradation pathway of phenolic compounds) at 463 K under 0.75 MPa oxygen partial pressure. The preparation parameter with the strongest impact on the gold particle size, the gold deposition yield, the chlorine removal efficiency and the gold catalyst performances was shown to be the final pH of the preparation, which strongly influenced the gold precursor speciation in solution and the interaction of the gold precursor with the titania support. Gold catalysts were shown to be very active, with about 80% of the succinic acid which is converted being directly mineralized. Furthermore, gold catalysts appeared to be somehow very selective in acetic acid with only traces of acrylic acid being intermediately produced upon succinic acid degradation. The most active catalyst was prepared via deposition–precipitation using ammonia and was shown to be only 3 times less active than the best performing ruthenium catalysts. Unfortunately, the gold catalyst rapidly deactivated upon time on stream, probably due to the intrinsic gold instability under the applied reaction conditions.

An optimized route for the preparation of well dispersed supported ruthenium catalysts

The preparation of ceria and ceria–zirconia supported ruthenium catalysts was optimized in order to get well-dispersed metal particles. The influence of the preparation method and the treatment conditions on the final morphology of the catalyst was investigated. Ceria-supported catalysts, prepared by incipient wetness impregnation under ultrasound and further treated under pure hydrogen, were shown to have an optimal metal dispersion. In fact, H2 chemisorption results and TEM observations demonstrated a large increase in the metal accessibility when impregnation was carried out with ultrasound assistance. Ceria-supported ruthenium catalysts with dispersion as high as 60% were prepared.

Sibunit-based catalytic materials for the deep oxidation of organic ecotoxicants in aqueous solution: I. Surface properties of the oxidized sibunit samples

This article presents the first systematic study of the effect of oxidation under various conditions on the surface composition and catalytic properties of a carbon material of the Sibunit family (which is promising for oxidative treatment of industrial wastewater) in deep oxidation of organic ecotoxicants in aqueous solution. Modification of the surface properties and texture of Sibunit-4 by various oxidative treatment procedures using nitric acid, sodium hypochlorite, hydrogen peroxide, or oxygen as the oxidant is reported. The chemical state of the surface of oxidized Sibunit and its texture have been investigated by a combination of physical and chemical methods (XPS, acid-base titration with bases differing in strength, pH slurry measurements, determination of pH at the point of zero charge, and low-temperature N2 adsorption). By using different oxidation procedures, it is possible to obtain oxidized Sibunit samples with variable concentrations and natures of oxygen-containing surface groups.

Oxygen storage and oxygen mobility on ceria and ceria-zirconia supported noble metals

N2 adsorption at 77K, TEM and Hz chemisorption. Both the oxygen storage capacity (OSC) and the activity in the *0/160 isotopic homoexchange reaction were measured on fresh and aged-catalysts. Interestingly, Ir was found to be responsible for the largest OSC enhancement. For all catalysts, large metal particles were shown to be more reactive. Looking at oxygen activation on metal particles, Ir and Rh appear to behave differently. Ir catalysts activity in the homoexchange reaction was found to be independent on the underlying support. On the opposite, a comparison between OSC and isotopic homoexchange results evidenced a strong metaVsupport interaction in the case of Rh catalysts. 1. INTRODUCTION In the past decades, many studies have been performed in the field of environmental catalysis. Evolution towards stricter regulations on automotive pollution control implied an optimization of Three-Way Catalysts (TWC) which operate under transient conditions. One key parameter is the oxygen storage. Cerium-zirconium solid solutions were shown to be good candidates with enlarged Oxygen-Storage Capacity (OSC) and improved redox properties [l-61. However, only a few studies have been devoted to understand oxygen storage processes

Sibunit-based catalytic materials for the deep oxidation of organic ecotoxicants in aqueous solutions. II: Wet peroxide oxidation over oxidized carbon catalysts

The influence of the surface chemical composition of carbon catalysts prepared by oxidative treatment on the basis of the Sibunit-4 carbon material of the Sibunit family on their catalytic properties in the liquid-phase oxidation of formic acid by hydrogen peroxide was studied for the first time. Pure carbon samples were found to be active in the destruction of hydrogen peroxide and the oxidation of an organic substrate, and their activity decreased with an increase in the number of carboxyl and lactone groups on the surface of a carbon catalyst. Nevertheless, the rates of such processes on carbon catalysts are lower than in the presence of even small amounts of homogeneous Fe3+. It was shown that carbon samples accelerate or (to the contrary) inhibit the Fe3+-catalyzed peroxide oxidation of an organic substance, depending on the quantitative ratio of surface carboxyl and lactone groups and Fe3+ ions in the reaction solution. Possible acceleration and inhibition mechanisms for peroxide oxidation on carbon catalysts are discussed. The established influence of the surface chemical properties of carbon catalysts must be taken into account in the development of catalysts and processes for the oxidative purification of industrial wastewater.

Phenolic compounds removal by wet air oxidation based processes

Wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) are efficient processes to degrade organic pollutants in water. In this paper, we especially reviewed the WAO and CWAO processes for phenolic compounds degradation. It provides a comprehensive introduction to the CWAO processes that could be beneficial to the scientists entering this field of research. The influence of different reaction parameters, such as temperature, oxygen pressure, pH, stirring speed are analyzed in detail; Homogenous catalysts and heterogeneous catalysts including carbon materials, transitional metal oxides and noble metals are extensively discussed, among which Cu based catalysts and Ru catalysts were shown to be the most active. Three different kinds of the reactor implemented for the CWAO (autoclave, packed bed and membrane reactors) are illustrated and compared. To enhance the degradation efficiency and reduce the cost of the CWAO process, biological degradation can be combined to develop an integrated technology.

Sibunit-based catalytic materials for the deep oxidation of organic ecotoxicants in aqueous solutions. III: Wet air oxidation of phenol over oxidized carbon and Rr/C catalysts

This article presents the first systematic study concerning the effect of the oxidative treatment conditions on the surface chemical composition and the catalytic properties in the deep wet oxidation of organic ecotoxicants of a Sibunit type carbon material (S4) which was earlier identified as promising for the oxidative treatment of industrial wastewaters. The influence of the surface chemistry of the carbon materials oxidized under different conditions on the catalytic performances in the wet air oxidation of phenol of the bare carbon materials as well as the ruthenium-containing catalysts (3 wt % Ru) supported on the oxidized carbon samples was studied. The catalytic activity of the bare carbon samples appeared to be moderate and either (i) increased with the total number of carbonyl and phenolic surface groups or (ii) decreased with the total concentration of surface carboxylic and lactonic species. However, the catalytic performances of the Ru-containing catalysts were significantly higher. Based on our results, an optimum pretreatment of the carbon support could be identified to obtain the most stable and active Sibunit-supported ruthenium catalysts in the wet air oxidation of phenols.