Jean-François Lamonier

Formaldehyde: catalytic oxidation as a promising soft way of elimination.

Compared to other molecules such as benzene, toluene, xylene, and chlorinated compounds, the catalytic oxidation of formaldehyde has been studied rarely. However, standards for the emission level of this pollutant will become more restrictive because of its extreme toxicity even at very low concentrations in air. As a consequence, the development of a highly efficient process for its selective elimination is needed. Complete catalytic oxidation of formaldehyde into CO2 and H2 O using noble-metal-based catalysts is a promising method to convert this pollutant at room temperature, making this process energetically attractive from an industrial point of view. However, the development of a less expensive active phase is required for a large-scale industrial development. Nanomaterials based on oxides of manganese are described as the most promising catalysts. The objective of this Minireview is to present promising recent studies on the removal of formaldehyde through heterogeneous catalysis to stimulate future research in this topic.

Removal of oxygenated volatile organic compounds by catalytic oxidation over Zr-Ce-Mn catalysts.

The composition-activity relationship of Zr-Ce-Mn-O materials was investigated for the catalytic removal of Oxygenated Volatile Organic Compounds (OVOC) emitted by stationary sources. Using a sol-gel method, very high surface specific areas, small crystallite sizes and high redox properties were obtained for Zr(0.4)Ce(0.6-x)Mn(x)O(2) catalytic systems after calcination at 500°C. The textural and redox properties were improved when Mn content increased in the material, especially for x=0.36. As a result the most active and selective catalyst in the butanol (model of OVOC) oxidation was obtained for the nominal composition Zr(0.4)Ce(0.24)Mn(0.36)O(2) due to a high oxygen mobility and surface Mn(4+) concentration.

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.

Transformation of tetragonal zirconia phase to monoclinic phase in the presence of Fe3+ ions as probes: an EPR study

EPR was mainly used to study the morphological, textural and structural behavior of zirconium hydroxide [ZrO(OH)2] with respect to calcination under air at different temperatures. For calcination temperatures less than 700°C, the tetragonal and monoclinic phases of the solid were present. In this range of temperatures an EPR signal with gxx=1.9755, gyy=1.9720 and gzz=1.9562 was observed and attributed to Zr3+ ions located in octahedral sites with strong tetragonal distortion. The dehydration of OH- groups from solids could be responsible for the Zr4+ reduction into Zr3+ ions. A second signal, centered at g=2.0018, was also observed and assigned to trapped single electrons located in oxygen vacancies of ZrO2. A third signal with gxx=2.0040, gyy=2.0082 and gzz=2.0334 was attributed to adsorbed O2- species. Finally, a fourth signal obtained at low magnetic field with different g values was attributed to Fe3+ ions located in sites with a purely rhombic field. For high calcination temperatures (>700°C), the tetragonal phase was completely transformed into monoclinic phase. In this phase, the trapped single electrons and the adsorbed O2- species disappeared whereas the number of Zr3+ ions increases when compared to that obtained at lower calcination temperatures. This increase could be related to the reduction of Zr4+ by the trapped single electrons and the formation of the monoclinic phase which stabilizes the Zr3+ ions. In this latter phase, the Fe3+ ions are located in sites which have the same environmental symmetry than in tetragonal phase but with specific EPR parameter values.

Structural, textural and acid–base properties of carbonate-containing hydroxyapatites

Carbonate-containing hydroxyapatites with different Ca/P ratios and optionally containing Na+ cations were successfully synthesized using a precipitation method. The solids were extensively characterized by XRD, LEIS, XPS, IR, TGA and NMR. Further, their acid–base properties were determined by NH3-TPD, PEA-XPS, CO2-TPD and by pulsed liquid chromatography using benzoic acid as a probe. The so-obtained structural, textural and acid–base properties could be finely correlated to give a clear picture of the system. The acidic properties of hydroxyapatites were attributed to Ca2+, surface HPO42− and OH− vacancies and the basic properties were attributed to PO43−, OH− and CaO species. The fine-tuning of the amount, of the nature and the strength of acid–base properties derived by varying the carbonate content in hydroxyapatites can find applications in catalysis, which was illustrated by isopropanol reactivity.

Mesoporous Silica‐Confined Manganese Oxide Nanoparticles as Highly Efficient Catalysts for the Low‐Temperature Elimination of Formaldehyde

Manganese(IV) oxide was synthesized through crystallization in confined space by using the SBA‐15 silica support. The evolution of textural, morphological, structural, and redox properties of the manganese phase in the composites has been studied in terms of different parameters such as impregnation route, manganese loading, and activation temperature. High performances of nanoscaled manganese(IV) oxide for low‐temperature formaldehyde oxidation have been obtained. The optimization of preparation parameters enabled the complete conversion of formaldehyde at temperatures as low as 130 °C, which is comparable to the activity of the reference platinum catalyst that demonstrates complete conversion at similar temperatures.

Reactivity of ethanol over hydroxyapatite-based Ca-enriched catalysts with various carbonate contents

The Guerbet reaction of ethanol to produce heavier products was performed over a series of extensively characterized carbonate-containing hydroxyapatites (HAPs) with different Ca/P ratios and thus different densities, strengths and natures of acid and basic sites. These properties were correlated with the reactivity of the solids and an optimal ratio between the amount of acid and basic sites was evidenced (ca. 5). The best performance was accordingly obtained over the Hap-CO3 catalyst, which gave a yield of 30% of heavier alcohols at 40% ethanol conversion.

Capture of formaldehyde by adsorption on nanoporous materials

The aim of this work is to assess the capability of a series of nanoporous materials to capture gaseous formaldehyde by adsorption in order to develop air treatment process and gas detection in workspaces or housings. Adsorption-desorption isotherms have been accurately measured at room temperature by TGA under very low pressure (p<2 hPa) on various adsorbents, such as zeolites, mesoporous silica (SBA15), activated carbon (AC NORIT RB3) and metal organic framework (MOF, Ga-MIL-53), exhibiting a wide range of pore sizes and surface properties. Results reveal that the NaX, NaY and CuX faujasite (FAU) zeolites are materials which show strong adsorption capacity and high affinity toward formaldehyde. In addition, these materials can be completely regenerated by heating at 200°C under vacuum. These cationic zeolites are therefore promising candidates as adsorbents for the design of air depollution process or gas sensing applications.

Combustion synthesis of LaMn1−xAlxO3+δ (0 ≤ x ≤ 1): tuning catalytic properties for methane deep oxidation

The objective of this work was to study the effect of aluminum incorporation into the B sublattice of lanthanum manganite on the thermal stability and catalytic activity in CH4 complete oxidation in relation to the physico-chemical properties. Single-step solution combustion synthesis under stoichiometric conditions of glycine/nitrate was used to prepare LaMn1−xAlxO3+δ oxides (0 ≤ x ≤ 1). The obtained powders were characterized by XRD, SEM, TPD-O2 and XPS techniques and tested as catalysts in the deep oxidation of methane. XRD analysis showed a crystallized single perovskite phase over a large domain of aluminum content (x ≤ 95%). The specific surface area decreases with the incorporation of aluminum into the perovskite lattice and shows optimum value for x = 0.1. All the Mn-containing oxides exhibit oxidative non-stoichiometry and a mixture of Mn4+–Mn3+. Compared to the bulk, a decrease in surface element enrichment and an increase in the superficial Mn4+/Mn3+ ratio were observed with a progressive introduction of aluminum into the perovskite lattice. Catalytic activity of Al-doped oxides was governed by the superficial Mn concentration and the amount of desorbed oxygen involved in Mn4+ ↔ Mn3+ redox reactions. These parameters were found to be optimal for the best catalyst obtained with x = 0.1 which also proved to be the most stable catalyst.

AN EPR INVESTIGATION ON THE REACTIVITY OF OXYGEN FROM CERIA MODIFIED BIMETALLIC PT-RH/AL2O3 CATALYSTS IN THE CO + NO REACTION

Abstract The CO+NO reaction has been studied on Pt-Rh/Al2O3-CeO2 at PNO=5.6×10−3 atm and PCO=5×10−3 atm between 25 and 500°C. EPR technique was used to investigate the mechanism of this reaction. O2− species were detected after reaction and it seems that their formation is closely related to changes in catalytic performances of Pt-Rh/Al2O3-CeO2.