Structural and Morphological Characterization of Alumina Supported Pd Nanoparticles Obtained by Colloidal Synthesis

Alumina supported Palladium nanoparticles catalysts have been prepared by colloidal synthesis. The characterization of the structure and the morphology of the obtained nanoparticles is done by a two step procedure. In a first step, the possible morphologies of the particles are derived from physical principles. High Resolution Transmission Electron Microscopy (HRTEM) images and X-Ray Diffraction (XRD) diagrams are simulated. Simulations allows us to evaluate the limits of both methods to characterize such samples. We show that HRTEM is able to distinguish between the possible morphologies but is not sufficient to characterize vacancies or surface defects. We demonstrate that XRD is a good complementary technique, able also to obtain information about structure, morphology and size even for such small objects. In a second step, simulations are compared with experimental results. We show that two modes of synthesis, acidic and basic, lead to the same structure and morphology of nanoparticles. PdO nanoparticles present an octahedral shape close to 2 nm. The metallic Pd nanoparticles are always observed as cuboctahedra close to 2 nm. This same structure for both modes of synthesis cannot explain the differences of catalytic activity observed in the literature [Didillon B. et al. (1998) Stud. Surf. Sci. Catal., 118, 41-54]. The aggregation state of the individual synthesized particles is thus introduced to account for the differences in the catalytic performance

3D Chemical Distribution of Titania-Alumina Catalyst Supports Prepared by the Swing-pH Method

cited By 3International audienceAnalytical electron tomography combined with more classical techniques such as X-ray fluorescence and X-ray photoelectron spectroscopy were performed with a series of titania-alumina catalyst supports prepared by using the swing-pH method. The bulk proportion of titania and alumina was varied along the sample series. It was observed that, independently of this bulk proportion, only 30 % of the surface of the grains of the resulting catalysts was titania covered. It was also shown that the porosity of the material was driven by alumina, and for low titania contents, alumina formed a layer close the surface of the grains. At concentrations higher than 30 % titania, the layer was broken and aggregates covered by alumina were formed, which may have an impact on catalysis if these materials are used as supports for an active phase. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Dry Gel Conversion Synthesis of Zeolite EU-1 from Low Alkali Containing Precursors

Congrès du 12.08.2007 au 17.08.200

Synthèse de la zéolithe EU-1 à partir de précurseurs pauvres en Na2O par la méthode «Dry Gel Conversion»

Congrès : du 29.05.2007 au 01.06.200

Zn(II), Mn(II) and Sr(II) Behavior in a Natural Carbonate Reservoir System. Part I: Impact of Salinity, Initial pH and Initial Zn(II) Concentration in Atmospheric Conditions

The sorption of inorganic elements on carbonate minerals is well known in strictly controlled conditions which limit the impact of other phenomena such as dissolution and/or precipitation. In this study, we evidence the behavior of Zn(II) (initially in solution) and two trace elements, Mn(II) and Sr(II) (released by carbonate dissolution) in the context of a leakage from a CO2 storage site. The initial pH chosen are either equal to the pH of the water-CO2 equilibrium (~ 2.98) or equal to the pH of the water-CO2-calcite system (~ 4.8) in CO2 storage conditions. From this initial influx of liquid, saturated or not with respect to calcite, the batch experiments evolve freely to their equilibrium, as it would occur in a natural context after a perturbation. The batch experiments are carried out on two natural carbonates (from Lavoux and St-Emilion) with PCO2 = 10−3.5 bar, with different initial conditions ([Zn(II)]i from 10−4 to 10−6 M, either with pure water or 100 g/L NaCl brine). The equilibrium regarding calcite dissolution is confirmed in all experiments, while the zinc sorption evidenced does not always correspond to the two-step mechanism described in the literature. A preferential sorption of about 10% of the concentration is evidenced for Mn(II) in aqueous experiments, while Sr(II) is more sorbed in saline conditions. This study also shows that this preferential sorption, depending on the salinity, is independent of the natural carbonate considered. Then, the simulations carried out with PHREEQC show that experiments and simulations match well concerning the equilibrium of dissolution and the sole zinc sorption, with log KZn(II) ~ 2 in pure water and close to 4 in high salinity conditions. When the simulations were possible, the log K values for Mn(II) and Sr(II) were much different from those in the literature obtained by sorption in controlled conditions. It is shown that a new conceptual model regarding multiple Trace Elements (TE) sorption is required, to enable us to better understand the fate of contaminants in natural systems

Zn(II), Mn(II) and Sr(II) Behavior in a Natural Carbonate Reservoir System. Part II: Impact of Geological CO

Some key points still prevent the full development of geological carbon sequestration in underground formations, especially concerning the assessment of the integrity of such storage. Indeed, the consequences of gas injection on chemistry and petrophysical properties are still much discussed in the scientific community, and are still not well known at either laboratory or field scale. In this article, the results of an experimental study about the mobilization of Trace Elements (TE) during CO2 injection in a reservoir are presented. The experimental conditions range from typical storage formation conditions (90 bar, supercritical CO2) to shallower conditions (60 and 30 bar, CO2 as gas phase), and consider the dissolution of the two carbonates, coupled with the sorption of an initial concentration of 10−5 M of Zn(II), and the consequent release in solution of Mn(II) and Sr(II). The investigation goes beyond the sole behavior of TE in the storage conditions: it presents the specific behavior of each element with respect to the pressure and the natural carbonate considered, showing that different equilibrium concentrations are to be expected if a fluid with a given concentration of TE leaks to an upper formation. Even though sorption is evidenced, it does not balance the amount of TE released by the dissolution process. The increase in porosity is clearly evidenced as a linear function of the CO2 pressure imposed for the St-Emilion carbonate. For the Lavoux carbonate, this trend is not confirmed by the 90 bar experiment. A preferential dissolution of the bigger family of pores from the preexisting porosity is observed in one of the samples (Lavoux carbonate) while the second one (St-Emilion carbonate) presents a newly-formed family of pores. Both reacted samples evidence that the pore network evolves toward a tubular network type

Diffusion of asphaltene molecules through the pore structure of hydroconversion catalysts

Tayakout, M. Ferreira, C. Espinat, D. Picon, S. Arribas Sorbier, L. Guillaume, D. Guibard, I.When hydrotreatment of heavy cuts by heterogeneous catalysis is carried out in liquid phase the, molecules' state of containment in the porous network is very high. Moreover, at that state of containment, the size of asphaltenes and resins, from various origins, can be the cause for the different hydrotreatment yields. Consequently, volume constraints are added to the kinetic and thermodynamic ones (adsorption equilibrium): a given species can penetrate in the solid only if the necessary volume is available within the network. Hindered diffusion and adsorption of asphaltene molecules inside hydrotreatment catalysts' carriers were studied. The system's kinetics was investigated by visible absorption spectroscopy. Asphaltenes were prepared by n-heptane separation and solubilized in toluene at a known concentration and put in contact with a given amount of catalyst support. The evolution of the concentration in the asphaltene's solution was followed, as a function of time, by measuring the absorbance of a monochromatic visible radiation (750 nm) through the asphaltene suspension. A model based on the "Stefan-Maxwell" equations, that takes into account the volume constraints by the Fornasiero's formulation, which supposes that the molecules collide only by equivalent volume, was developed. The parameters estimation has been performed and discussed. The results show that the diffusional limitations are important in the catalyst used for heavy oil hydrotreatment and the asphaltene adsorption is very strong in this type of material. (C) 2009 Elsevier Ltd. All rights reserved

3D-TEM investigation of the nanostructure of a delta-Al2O3 catalyst support decorated with Pd nanoparticles

The electron tomography technique applied in a quantitative way allowed us to characterize a heterogeneous catalyst made of Pd nanoparticles deposited on a delta-Al2O3 lamellar support. In the first step, high resolution tomographic experiments carried out on several typical areas of support have confirmed the hypothesis of formation of delta-Al2O3 proposed in the literature by the coalescence of lateral facets of the gamma-Al2O3 precursor. A bimodal porosity was also observed in the arrangement of delta-Al2O3 platelets. In the second step, the Pd nanoparticles were found preferentially anchored on the lateral facets of delta-Al2O3 platelets or on the defects situated on their basal planes. From a general point of view, we have demonstrated once again that the electron tomography technique implemented with nanometre resolution provides unique insight into the structure, morphology and spatial arrangement of components in a complex 3D nanostructure