Heterogeneous catalysts preparation in ionic liquid media : titania-supported metallic nanoparticles (Au and Au-Pd)

Ces travaux portent sur l'élaboration de catalyseurs hétérogènes en milieu liquide ionique (LI). Ces sels liquides à température ambiante permettent d'ajuster les propriétés du solvant suivant la composition chimique du LI mis en jeu (sels d'imidazolium ou Deep Eutectic Solvent à base de chlorure de choline et urée). Ce type de solvant a permis la synthèse et le dépôt de nanoparticules (NPs) d'Au et Au-Pd sur TiO2. Le type de LI utilisé influence la stabilité des NPs en solution, la force de l'interaction métal/support et la nanostructuration des particules bimétalliques. Les performances catalytiques en hydrogénation sélective du butadiène ont montré une amélioration de l'activité des catalyseurs monométalliques à base d'Au en présence de Pd, une promotion de l'activité des catalyseurs (mono-et bimétalliques) par des espèces phosphorées résiduelles issues du LI et une inhibition de l'activité par des espèces soufrées. Des supports TiO2 ont également été préparés en milieu DES. L'utilisation de ce LI et d'un précurseur de Ti spécifique a permis de contrôler la texture et la structure du polymorphe obtenu (anatase, rutile ou mélange anatase-rutile). L'influence de la nature du support a été étudiée en oxydation du CO après dépôt d'Au par dépôt-précipitation à l'urée. Les catalyseurs Au/TiO2 les plus actifs ont été obtenus pour des mélanges anatase-rutile, la proximité entre phases anatase et rutile menant à un optimum de réactivité et de stabilité.This work deals with the elaboration of heterogeneous catalysts in ionic liquids (ILs). These salts, liquid at room temperature, were chosen because they permit to adjust the solvent properties depending on their chemical composition (imidazolium salts or Deep Eutectic Solvent based on choline chloride and urea). These solvents allowed the synthesis and deposition of Au and Au-Pd nanoparticles (NPs) on TiO2. The IL nature controls the NPs stability in solution, the strength of the metal/support interaction and the nanostructuration of bimetallic particles. The catalysts performances, evaluated by selective hydrogenation, showed an increase in activity of the Au monometallic catalysts after addition of Pd, a promotion of the catalysts activity due to the presence of P residues from the ILs and an inhibition of the activity caused by S species. TiO2 supports were also prepared in DES. The use of this IL, in addition to a specific Ti precursor, led to a textural and structural control of the obtained polymorphs (anatase, rutile or anatase-rutile mixture). The influence of the support type was studied in CO oxidation after Au deposition by urea deposition-precipitation. The most active Au/TiO2 catalysts were obtained with anatase-rutile mixtures, the vicinity between anatase and rutile phases leading to an optimum activity and stability.This work deals with the elaboration of heterogeneous catalysts in ionic liquids (ILs). These salts, liquid at room temperature, were chosen because they permit to adjust the solvent properties depending on their chemical composition (imidazolium salts or Deep Eutectic Solvent based on choline chloride and urea). These solvents allowed the synthesis and deposition of Au and Au-Pd nanoparticles (NPs) on TiO2. The IL nature controls the NPs stability in solution, the strength of the metal/support interaction and the nanostructuration of bimetallic particles. The catalysts performances, evaluated by selective hydrogenation, showed an increase in activity of the Au monometallic catalysts after addition of Pd, a promotion of the catalysts activity due to the presence of P residues from the ILs and an inhibition of the activity caused by S species. TiO2 supports were also prepared in DES. The use of this IL, in addition to a specific Ti precursor, led to a textural and structural control of the obtained polymorphs (anatase, rutile or anatase-rutile mixture). The influence of the support type was studied in CO oxidation after Au deposition by urea deposition-precipitation. The most active Au/TiO2 catalysts were obtained with anatase-rutile mixtures, the vicinity between anatase and rutile phases leading to an optimum activity and stability

Elaboration de catalyseurs hétérogènes en milieu liquide ionique : nanoparticules métalliques (Au et Au-Pd) supportées sur dioxyde de titane

This work deals with the elaboration of heterogeneous catalysts in ionic liquids (ILs). These salts, liquid at room temperature, were chosen because they permit to adjust the solvent properties depending on their chemical composition (imidazolium salts or Deep Eutectic Solvent based on choline chloride and urea). These solvents allowed the synthesis and deposition of Au and Au-Pd nanoparticles (NPs) on TiO2. The IL nature controls the NPs stability in solution, the strength of the metal/support interaction and the nanostructuration of bimetallic particles. The catalysts performances, evaluated by selective hydrogenation, showed an increase in activity of the Au monometallic catalysts after addition of Pd, a promotion of the catalysts activity due to the presence of P residues from the ILs and an inhibition of the activity caused by S species. TiO2 supports were also prepared in DES. The use of this IL, in addition to a specific Ti precursor, led to a textural and structural control of the obtained polymorphs (anatase, rutile or anatase-rutile mixture). The influence of the support type was studied in CO oxidation after Au deposition by urea deposition-precipitation. The most active Au/TiO2 catalysts were obtained with anatase-rutile mixtures, the vicinity between anatase and rutile phases leading to an optimum activity and stability.This work deals with the elaboration of heterogeneous catalysts in ionic liquids (ILs). These salts, liquid at room temperature, were chosen because they permit to adjust the solvent properties depending on their chemical composition (imidazolium salts or Deep Eutectic Solvent based on choline chloride and urea). These solvents allowed the synthesis and deposition of Au and Au-Pd nanoparticles (NPs) on TiO2. The IL nature controls the NPs stability in solution, the strength of the metal/support interaction and the nanostructuration of bimetallic particles. The catalysts performances, evaluated by selective hydrogenation, showed an increase in activity of the Au monometallic catalysts after addition of Pd, a promotion of the catalysts activity due to the presence of P residues from the ILs and an inhibition of the activity caused by S species. TiO2 supports were also prepared in DES. The use of this IL, in addition to a specific Ti precursor, led to a textural and structural control of the obtained polymorphs (anatase, rutile or anatase-rutile mixture). The influence of the support type was studied in CO oxidation after Au deposition by urea deposition-precipitation. The most active Au/TiO2 catalysts were obtained with anatase-rutile mixtures, the vicinity between anatase and rutile phases leading to an optimum activity and stability.Ces travaux portent sur l'élaboration de catalyseurs hétérogènes en milieu liquide ionique (LI). Ces sels liquides à température ambiante permettent d'ajuster les propriétés du solvant suivant la composition chimique du LI mis en jeu (sels d'imidazolium ou Deep Eutectic Solvent à base de chlorure de choline et urée). Ce type de solvant a permis la synthèse et le dépôt de nanoparticules (NPs) d'Au et Au-Pd sur TiO2. Le type de LI utilisé influence la stabilité des NPs en solution, la force de l'interaction métal/support et la nanostructuration des particules bimétalliques. Les performances catalytiques en hydrogénation sélective du butadiène ont montré une amélioration de l'activité des catalyseurs monométalliques à base d'Au en présence de Pd, une promotion de l'activité des catalyseurs (mono-et bimétalliques) par des espèces phosphorées résiduelles issues du LI et une inhibition de l'activité par des espèces soufrées. Des supports TiO2 ont également été préparés en milieu DES. L'utilisation de ce LI et d'un précurseur de Ti spécifique a permis de contrôler la texture et la structure du polymorphe obtenu (anatase, rutile ou mélange anatase-rutile). L'influence de la nature du support a été étudiée en oxydation du CO après dépôt d'Au par dépôt-précipitation à l'urée. Les catalyseurs Au/TiO2 les plus actifs ont été obtenus pour des mélanges anatase-rutile, la proximité entre phases anatase et rutile menant à un optimum de réactivité et de stabilité

Heterogeneous catalyst preparation in ionic liquids: Titania supported gold nanoparticles

International audienceThis work reports the use of ionic liquids (ILs) as solvent for the synthesis of Au/TiO2 heterogeneous catalysts. It is shown that the versatility of the physico-chemical properties of ILs makes them interesting solvents for a broad control of supported metal nanoparticles (NPs) size and for a fine-tuning of metal–support interaction. Synthesis and deposition of Au NPs on TiO2 are carried out through a colloidal route in imidazolium-based ILs (1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) and trifluoromethanesulfonate (BMIMOTf)) and in a Deep Eutectic Solvent (DES, choline chloride and urea). The stabilization of the dispersed NPs and their deposition on an oxide carrier is investigated in pure ILs and in the presence of extra stabilizing agents (1-methylimidazole or polyvinylpyrrolidone). In the absence of TiO2, the NPs stability varies with the composition of the IL (BMIMOTf > BMIMPF6 > DES) and is critically depending on the addition of an extra stabilizing agent (SA). Conversely, when gold NPs are synthesized in the presence of TiO2 in imidazolium ILs, the addition of a SA is no longer required since the oxide support acts as a stabilizer for the gold colloids and prevents aggregation of NPs. A detailed XPS investigation of the surface composition of the TiO2-supported gold catalysts shows that the cationic part of the imidazolium ILs on the one hand and urea in DES on the other hand are co-adsorbed with gold NPs upon deposition on TiO2, probably decorating and stabilizing the Au NPs. The fate of the anionic part of the ILs (PF6−, OTf− and Cl−) is highly depending on the type of IL. Limited surface adsorption is reported for triflate (BMIMOTf) and chloride anions (DES), the latter being fully removed upon calcination, while PF6− (BMIMPF6) remains adsorbed on the surface during Au NPs deposition and leads to POxδ− and F− surface species upon calcination. The surface composition controls the intrinsic catalytic activity (TOF) in the selective hydrogenation of butadiene. It is shown that the surface doping of supported Au NPs with P and F anionic deposits (synthesized in BMIMPF6) has a promoting effect for the intrinsic catalytic activity

Sulfidation Processes of PVP-Coated Silver Nanoparticles in Aqueous Solution: Impact on Dissolution Rate

PMID: 21598969International audienceDespite the increasing use of silver nanoparticles (Ag-NPs) in nanotechnology and their toxicity to invertebrates, the transformations and fate of Ag-NPs in the environment are poorly understood. This work focuses on the sulfidation processes of PVP-coated Ag-NPs, one of the most likely corrosion phenomena that may happen in the environment. The sulfur to Ag-NPs ratio was varied in order to control the extent of Ag-NPs transformation to silver sulfide (Ag2S). A combination of synchrotron-based X-ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure spectroscopy shows the increasing formation of Ag2S with an increasing sulfur to Ag-NPs ratio. TEM observations show that Ag2S forms nanobridges between the Ag-NPs leading to chain-like structures. In addition, sulfidation strongly affects surface properties of the Ag-NPs in terms of surface charge and dissolution rate. Both may affect the reactivity, transport, and toxicity of Ag-NPs in soils. In particular, the decrease of dissolution rate as a function of sulfide exposure may strongly limit Ag-NPs toxicity since released Ag+ ions are known to be a major factor in the toxicity of Ag-NPs

Impact of Fatty Triamine on Friction Reduction Performance of MoDTC Lubrication Additive

The impact of a fatty triamine (Triameen YT) additive was investigated on the friction performance and stability of molybdenum dithiocarbamate (MoDTC) in the formulations containing polyalphaolefin synthetic base oil (PAO) and zinc dialkyldithiophosphate (ZDDP). Triamine has no significant effect when mixed with MoDTC and ZDDP, but it improves the performance of MoDTC alone. However, in the MoDTC—Triamine—PAO solutions, a chemical reaction easily occurred and a reddish precipitate was formed upon storage. According to IR, XPS, TEM, and XAS characterizations, this precipitate is poorly crystalline layered alkylammonium oxothiomolybdate. Formation of the precipitate impaired the tribological performance by decreasing the number of active species delivered at the sliding contact interface. However, low friction coefficients were recovered by redispersion of the precipitate in PAO

Impact of Fatty Triamine on Friction Reduction Performance of MoDTC Lubrication Additive

The impact of a fatty triamine (Triameen YT) additive was investigated on the friction performance and stability of molybdenum dithiocarbamate (MoDTC) in the formulations containing polyalphaolefin synthetic base oil (PAO) and zinc dialkyldithiophosphate (ZDDP). Triamine has no significant effect when mixed with MoDTC and ZDDP, but it improves the performance of MoDTC alone. However, in the MoDTC—Triamine—PAO solutions, a chemical reaction easily occurred and a reddish precipitate was formed upon storage. According to IR, XPS, TEM, and XAS characterizations, this precipitate is poorly crystalline layered alkylammonium oxothiomolybdate. Formation of the precipitate impaired the tribological performance by decreasing the number of active species delivered at the sliding contact interface. However, low friction coefficients were recovered by redispersion of the precipitate in PAO