Élaboration de nanoparticules par ablation laser de cibles métalliques en milieu liquide et applications en catalyse

Nous avons élaboré des nanoparticules par ablation laser en milieux liquides, avec un laser YAG ( = 532 nm, pulse : 10Hz, 8ns, 40mJ) focalisé sur des cibles métalliques (Ni, Pd, Au) et bimétalliques (Au75Ag25, Ni75Pd25). Les caractéristiques physico-chimiques des nanoparticules formées ont été étudiées par ICP, TEM, EDX, UV-vis, XPS et PIXE. Dans le cas d'une cible de Ni dans l'eau des nanoparticules NiO, dont la taille diminue avec le temps d'ablation laser, ont été obtenues. L'effet du solvant sur les caractéristiques des nanoparticules a été étudié pour le Pd (eau et toluène) et l'Au (eau et MCH). Dans le cas du Pd, les particules obtenues dans l'eau présentent la structure cfc attendue ; celles obtenues dans le toluène ont une structure différente et sont souvent enrobées de carbone. Ceci est parfois le cas pour les plus grosses particules d'Au synthétisées dans le MCH. Les colloïdes de Pd déposés sur a-Al2O3 ont été testés dans l'oxydation totale du méthane. Les colloïdes d'or dans le MCH, testés dans l'époxydation du trans-stilbène, ont montré une bonne activité et une très bonne sélectivité en époxyde des plus petites particules d'or non supportées. Dans le cas des bimétalliques, nous avons obtenu des nanoparticules Au-Ag de composition identique à celle de la cible ; pour Ni-Pd, les particules obtenues sont homogènes en composition, mais celle-ci varie en fonction du temps d'ablation, et tend vers la composition nominale de la cible pour les plus forts temps. En conclusion, l'ablation laser en milieu liquide s'avère prometteuse pour obtenir des nanoparticules en solution, qui peuvent trouver des applications en catalyse, en particulier en milieu liquideWe synthesized colloidal nanoparticles by laser ablation in liquids using a YAG laser ( = 532 nm, pulse : 10Hz, 8ns, 40mJ) focused on metallic (Ni, Pd, Au) and bimetallic (Au75Ag25, Ni75Pd25) targets. The physico-chemical characteristics of the nanoparticles formed in solution were studied by ICP, TEM, EDX, UV-vis, XPS and PIXE. For Ni target in water, NiO nanoparticles were obtained. Their mean size decreases when laser ablation time increases. The effect of the solvent on the nanoparticles characteristics was studied for a Pd target (water and toluene) and on Au target (water and MCH). In the case of Pd, the particles obtained in water present fcc structure ; those obtained in toluene have a different structure and are often coated with carbon. This is also the case for some of the larger Au particles synthesized in MCH. Pd aqueous colloids were disposited on a-Al2O3, and were tested in the reaction of total oxidation of methane. Gold colloids in MCH were used as-prepared in the reaction of epoxidation of trans-stilbene, showing a good activity and a very food selectivity towards epoxide for the smallest unsupported gold particles. For bi-metallic samples Au75Ag25 and Ni75Pd25. We succeeded in preparing Au-Ag nanoparticles with homogeneous composition, similar to the one of the target. For Ni-Pd, the particles obtained are homogeneous in composition but it depends on the time of ablation, and approaches the nominal composition of the target for the higest time of ablation. In concoulsion, laser ablation in liquids is a promising method to obtain solutions of nanoprticles, which may find applications, particularly for catalysis in liquid mediaLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Étude des effets de contraintes sur catalyseurs bimétalliques PDNI supportés

Pour étudier les effets de contraintes sur les propriétés catalytiques du palladium, des nanoparticules bimétalliques PdNi de structure cœur-coquille ont été synthétisées par voie chimique, caractérisées par EDS, MET, EXAFS, etc. et testées en hydrogénation du buta-1,3-diène. La structure cœur-coquille des particules et la contrainte en compression exercée sur les atomes de palladium de surface ont été mises en évidence par EXAFS. Selon les travaux de la littérature, l activité hydrogénante du palladium contraint est amplifiée pour des catalyseurs modèles PdNi. Mais cette amplification n est pas observée pour nos particules supportées. Par conséquent, plus que les contraintes en compression à proprement dites, les reconstructions de surface, induites par ces contraintes, semblent être à l origine de cette amplificationTo study strain effects on catalytic properties for supported particles, core-shell Ni-Pd bimetallic nanoparticles have been prepared by chemical synthesis, characterized by multiple techniques (EDS, TEM, EXAFS, etc.) and studied in buta-1,3-diene hydrogenation. The core-shell structure of Ni-Pd particles and the compressive stress induced on Pd surface atoms, due to its larger atomic radius compared to Ni, have been evidenced by EXAFS. On PdNi model catalysts, Pd activity is amplified. In our case, no amplification of the Pd activity is observed for a monolayer of strained Pd on Ni particles. As a consequence, compressive strain on Pd surface atoms of nanoparticles seems not to play a major role in the amplification of the activity for the buta-1,3-diene hydrogenation; surface reconstruction appearing on extended surfaces to relax the surface stress seems to be the key pointLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Bulk and surface core level binding energies in the Pt80Fe20(111) alloy

Core level photoemission spectroscopy of the Pt 4f {7}/{2} level is used to investigate the surface and bulk Pt environments in the ordered catalytic alloy Pt 80Fe 20. The results obtained support a LEED model of Pt segregation to the surface. This implies the presence of two Pt surface sites

Étude in situ de surfaces monocristallines Au et Pd-Au (adsorption du CO et de O2)

La catalyse par l or connaît un fort renouveau depuis une quinzaine d années. Ce travail s inscrit dans une démarche de compréhension de l adsorption, à l échelle atomique, des réactifs de la réaction d oxydation du monoxyde de carbone sur des surfaces monocristallines d or et d alliage palladium-or. De plus, il vise à caractériser les surfaces sous pression de gaz. Pour cela, des techniques d analyse /in situ /(STM, XPS, PM-IRRAS et SXRD), de développement récent, sont mises en œuvre de l ultravide jusqu à 500 Torr. Le CO s adsorbe sur les surfaces Au(110), Au(111) et Pd-Au(110) sur des sites linéaires -et pontés dans le cas du bimétallique. Cette adsorption induit de fortes modifications de l état (morphologie, structure, propriétés électroniques) de surface. Les reconstructions des surfaces sont décrites en fonction de p(CO). Si les surfaces monocristallines d or conservent leurs structure et morphologie d équilibre sous p(O_2 ), la surface d alliage voit croître l oxyde PdO suite à une ségrégation de palladiumInterest for catalysis by gold has grown since about fifteen years. This work fits within an approach to gain understanding, at atomic scale, of the adsorption of the gases participating in the oxidation of carbon monoxide on single-crystal surfaces of gold and palladium-gold alloy. Furthermore, the aim is to characterise surfaces under gas pressure. In order to do so, recently developed /in situ/ analysis techniques (STM, XPS, PM-IRRAS and SXRD) are operated from UHV conditions up to 500Torr. CO adsorbs on Au(110), Au(111) and Pd-Au(110) surfaces on top sites and also on bridge sites in the case of the bi-metallic surface. This adsorption induces strong modification of the surface characteristics (morphology, structure, electronic properties). Surface reconstructions are described as a function of p(CO). While the structure and the morphology of single-crystal gold surfaces remain unchanged under p(O_2 ), Pd segregation and subsequent surface PdO formation is observed for the alloy surfaceLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Physicochemical and Surface Properties of Alumina Supported Bimetallic Pd-Sn and Pd-Ga Catalysts

National @ SURFACES+EEH:FMO:PGE:NSP:FCAInternational audienceThe selective hydrogenation of highly unsaturated hydrocarbons is an important industrial process for purification of petrochemical feedstocks. In this field of research, a challenge is to develop a specific catalyst with the highest selectivity and good stability even at high conversion. Pd catalyst is mostly used in the selective hydrogenation of 1,3-butadiene due to the stronger adsorption of 1,3-butadiene than butenes on Pd surface [1]. Addition of a second metal to Pd catalyst is an efficient way to modify the structural and electronic properties of Pd so that the alkene selectivity is improved [2,3]. The physicochemical and surface properties of monometallic Pd and bimetallic Pd-Sn and Pd-Ga catalysts on mixed-phase (¸-ą) alumina [4] were investigated by means of Fourier transform infrared (FT-IR) spectroscopy of adsorbed CO, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The TEM and EDX results indicated that the bimetallic Pd-Sn and Pd-Ga catalysts were formed at the desired atomic ratios (1 and 3) between palladium and the second metal without significant changes in particle size compared to the monometallic Pd. The FT-IR of adsorbed CO and XPS results revealed a modification of the electronic properties of Pd surface sites depending on the type of the second metal added. The addition of a second metal to Pd resulted in a decrease in the adsorption strength of CO compared to monometallic Pd. This can be attributed to a dilution of the palladium sites at the surface of the catalyst particles. Concerning the addition of Sn, Pd3Sn revealed to be the best composition [5]. In the case of Ga a higher amount of Ga was necessary (i.e., Pd/Ga = 1) to induce a similar effect to that of Pd3Sn. REFERENCES 1. R S. Hub, L. Hilaire and R. Touroude, Applied Catalysis 36, 307-322 (1988). 2. R. Ohnishi, H. Suzuki and M. Ichikawa, Catalysis Letters 33, 341-348 (1995). 3. J. Goetz, M.A. Volpe, C.E. Gigola and R. Touroude, Journal of Catalysis 199, 338-345 (2001). 4. K. Pattamakomsan, K. Suriye, S. Dokjampa, N. Mongkolsiri, P. Praserthdam and J. Panpranot, Catalysis Communications 11, 311-316 (2010). 5. K. Pattamakomsan, E. Ehret, F. Morfin, P. Gélin, Y. Jugnet, S. Prakash, J.C. Bertolini, J. Panpranot and F.J. Cadete Santos Aires, Catalysis Today 164, 28-33 (2011)

Pd8Ni92(110) surface structure from surface X-ray diffraction. Surface evolution under hydrogen and butadiene reactants at elevated pressure.

International audienceThe (Nx1) reconstruction (N = 5-6) of the clean Pd8Ni92(110) surface has been investigated by surface X-ray diffraction. A good fit with experimental data collected under UHV conditions is obtained when introducing undulations in the outer dense rows, constituted mainly of Pd atoms which strongly segregate to the surface. This reconstruction can be regarded as a way to relax the strains induced on the bigger Pd surface atoms, at least partially. The modifications of the surface were studied under butadiene then hydrogen as well as during butadiene hydrogenation at elevated pressure at 300 K and the (Nx1) reconstruction was found to be still present. The main changes are observed under pure hydrogen and during butadiene hydrogenation

Severity of COVID-19 and survival in patients with rheumatic and inflammatory diseases: data from the French RMD COVID-19 cohort of 694 patients

International audienceObjectives: There is little known about the impact of SARS-CoV-2 on patients with inflammatory rheumatic and musculoskeletal diseases (iRMD). We examined epidemiological characteristics associated with severe disease, then with death. We also compared mortality between patients hospitalised for COVID-19 with and without iRMD.Methods: Individuals with suspected iRMD-COVID-19 were included in this French cohort. Logistic regression models adjusted for age and sex were used to estimate adjusted ORs and 95% CIs of severe COVID-19. The most significant clinically relevant factors were analysed by multivariable penalised logistic regression models, using a forward selection method. The death rate of hospitalised patients with iRMD-COVID-19 (moderate-severe) was compared with a subset of patients with non-iRMD-COVID-19 from a French hospital matched for age, sex, and comorbidities.Results: Of 694 adults, 438 (63%) developed mild (not hospitalised), 169 (24%) moderate (hospitalised out of the intensive care unit (ICU) and 87 (13%) severe (patients in ICU/deceased) disease. In multivariable imputed analyses, the variables associated with severe infection were age (OR=1.08, 95% CI: 1.05-1.10), female gender (OR=0.45, 95% CI: 0.25-0.80), body mass index (OR=1.07, 95% CI: 1.02-1.12), hypertension (OR=1.86, 95% CI: 1.01-3.42), and use of corticosteroids (OR=1.97, 95% CI: 1.09-3.54), mycophenolate mofetil (OR=6.6, 95% CI: 1.47-29.62) and rituximab (OR=4.21, 95% CI: 1.61-10.98). Fifty-eight patients died (8% (total) and 23% (hospitalised)). Compared with 175 matched hospitalised patients with non-iRMD-COVID-19, the OR of mortality associated with hospitalised patients with iRMD-COVID-19 was 1.45 (95% CI: 0.87-2.42) (n=175 each group).Conclusions: In the French RMD COVID-19 cohort, as already identified in the general population, older age, male gender, obesity, and hypertension were found to be associated with severe COVID-19. Patients with iRMD on corticosteroids, but not methotrexate, or tumour necrosis factor alpha and interleukin-6 inhibitors, should be considered as more likely to develop severe COVID-19. Unlike common comorbidities such as obesity, and cardiovascular or lung diseases, the risk of death is not significantly increased in patients with iRMD