Jean-Marc Giraudon

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.

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.

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.

Organometallic route to dimolybdenum carbide via a low-temperature pyrolysis of a dimolybdenum alkyne complex

Pyrolytic transformation of the complex Cp2Mo2(CO)4(dmad) (Cp=cyclopentadienyl, dmad=dimethylacetylenedicarboxylate) under hydrogen at 550 °C gives, after a passivation step, Mo2C with an excess of carbon and oxygen. These impurities can be withdrawn with an appropriate reductive post-treatment. Based on thermogravimetric analyses and pyrolysis mass spectroscopy performed on the precursor, a preliminary decomposition scheme has been proposed.

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.

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.

Mesoporous manganese oxide catalysts for formaldehyde removal: influence of the cerium incorporation

Abstract Manganese oxide mesoporous materials were prepared by using template assisted method followed by an acidic treatment. The cerium addition to manganese oxide mesoporous structure was also studied. All the solids were characterized by XRD and specific surface area and pore size distributions were calculated from nitrogen sorption studies. XRD results suggested the formation of the MnO x -CeO 2 solid solution with the fluorite-type structure. The BET surface area values and the pore size distributions allowed to conclude the important role of the surfactant by the creation of narrow mesopores in the material.

Synthesis of ditungsten carbide by controlled decomposition of Cp2W2(CO)4 (dmad) under a hydrogen atmosphere

Controlled decomposition studies of the bis(cyclopentadienyl)ditungsten(tetracarbonyl)-dimethylacetylenedicarboxylate (Cp2W2(CO)4(dmad)) under flowing hydrogen show that it totally decomposes at 600 °C for 2 h to give a pure bulk W2C as revealed by X-ray diffraction. Excess oxygen and carbon at the surface are detected by X-ray photoelectron spectroscopy. An in situ temperature-programmed X-ray diffraction experiment performed on Cp2W2(CO)4 (dmad) shows the detection temperature of W2C to be 600 °C, the sample being amorphous or microcrystalline below that temperature. Based on previous results obtained for the decomposition of Cp2Mo2(CO)4(dmad) on the one hand, and thermogravimetric and chromatographic analyses performed on Cp2W2(CO)4 (dmad), on the other, a decomposition scheme of the latter under hydrogen has been proposed.