highly selective, active and stable fischer-tropsch catalyst using entrapped iron nanoparticles in silicalite-1

SSCI-VIDE+ECI2D:ING+JHU:YSC:JMI:ATU:DFAInternational audienceWe describe here the synthesis of well controlled iron nanoparticles of 5 nm encapsulated in the walls of hollow silicalite-1. The encapsulation prevent the particle to sinter under reaction conditions leading to very high and stable Fe dispersion. In addition to the high activity, this catalyst is extremely selective as it does not produced CO2

highly selective, active and stable fischer-tropsch catalyst using entrapped iron nanoparticles in silicalite-1

SSCI-VIDE+ING+JHUNational audienceTypical Fe based catalysts have high metal loadings (>70 wt%) and contain many different phases, which strongly limit the establishment of structure-activity relationships. We describe here the synthesis of well controlled iron nanoparticles of 3.5 nm [1] encapsulated in the walls of hollow silicalite-1. The encapsulation prevents the particle to sinter under reaction conditions leading to a high and stable Fe dispersion. In addition to the high activity, this catalyst is extremely selective as it does not produce any CO2.High resolution tomography show silicalite-1 hollow single crystals (~100 nm width) with a narrow distribution of the iron particle size centered at 3.5 nm (cf. figure 1). FTS performances of the Fe@silicalite-1 (3.4%Fe) were measured at 250 °C, 20 bar and H2/CO = 2. In terms of activity per mass of iron the Fe@silicalite-1 catalyst is 10 times more active than a commercial catalyst. Besides the high activity, the catalyst did not produce any CO2 against 20% for the commercial catalyst. It also showed a very high C5+ selectivity. In contrast to all other known Fe-catalysts, this iron ship-in-the-bottle catalyst does not show activity for the water-gas-shift reaction during FTS. Non-significant sintering was observed with the exception of a few larger Fe particles present in the big zeolite cavity. Further analysis of this catalyst shall provide insights into the sites responsible for CO2 production, paving the way to a rational design of iron-based FTS catalysts

highly selective, active and stable fischer-tropsch catalyst using entrapped iron nanoparticles in silicalite-1

SSCI-VIDE+ING+JHUNational audienceAlthough already applied at industrial scale about one century ago, the Fischer-Tropsch process is gaining renewed interests as it is a key step for converting alternative feedstocks, including biomass to transportable fuels. Compared to Co-based catalysts, state of the art Fe catalysts show lower activity (per volume), lower selectivity as it produces a significant and undesirable quantity of CO2 and much faster deactivation. There is a need to develop more active, more selective and more stable Fe Fischer-Tropsch Synthesis (FTS) catalysts. Unfortunately, the origins of low selectivity and fast deactivation are still unclear. Typical Fe based catalysts have high metal loadings (>70 wt%) and contain many different phases, which strongly limit the establishment of structure-activity relationships. We describe here the synthesis of well controlled iron nanoparticles of 5 nm encapsulated in the walls of hollow silicalite-1. The encapsulation prevents the particle to sinter under reaction conditions leading to a high and stable Fe dispersion. In addition to the high activity, this catalyst is extremely selective as it does not produce any CO2.High resolution TEM (figure 1) and tomography show silicalite-1 hollow single crystals (~100 nm width) with a narrow distribution of the iron particle size centered at 5 nm. FTS performances of the Fe@silicalite-1 (3.4%Fe) were measured at 250°C, 20 bar and H2/CO = 2 (table 1). A commercial Fe FT catalyst (54.8%Fe, 2.7%Cu, 2.2%K, 0.03%Na, 7.0%Si) was also investigated for comparison. The activities, stabilities and product selectivities of these catalysts were tested several times over a period of 100 h runs. On a volume basis, the catalytic activity of the Fe@silicalite-1 catalyst displayed a low activity in CO conversion. It is due to the low metal amount e.g. 15 times less than the commercial catalyst and the lower powder density. However in terms of activity per mass of iron the Fe@silicalite-1 catalyst is ten times more active. Besides the high activity, the catalyst did not produce any CO2. It also showed a very high C5+ selectivity. In contrast to all other known Fe-catalysts, this iron ship-in-the-bottle catalyst does not show activity for the water-gas-shift reaction during FTS. After 100 hours under reactions, non-significant sintering was observed with the exception of a few larger Fe particles present in the big zeolite cavity.Further analysis of this catalyst shall provide insights into the sites responsible for CO2 production, paving the way to a rational design of iron-based FTS catalysts

highly selective, active and stable fischer-tropsch catalyst using entrapped iron nanoparticles in silicalite-1

SSCI-VIDE+ING+JHUNational audienceTypical Fe based catalysts have high metal loadings (>70 wt%) and contain many different phases, which strongly limit the establishment of structure-activity relationships. We describe here the synthesis of well controlled iron nanoparticles of 3.5 nm [1] encapsulated in the walls of hollow silicalite-1. The encapsulation prevents the particle to sinter under reaction conditions leading to a high and stable Fe dispersion. In addition to the high activity, this catalyst is extremely selective as it does not produce any CO2.High resolution tomography show silicalite-1 hollow single crystals (~100 nm width) with a narrow distribution of the iron particle size centered at 3.5 nm (cf. figure 1). FTS performances of the Fe@silicalite-1 (3.4%Fe) were measured at 250 °C, 20 bar and H2/CO = 2. In terms of activity per mass of iron the Fe@silicalite-1 catalyst is 10 times more active than a commercial catalyst. Besides the high activity, the catalyst did not produce any CO2 against 20% for the commercial catalyst. It also showed a very high C5+ selectivity. In contrast to all other known Fe-catalysts, this iron ship-in-the-bottle catalyst does not show activity for the water-gas-shift reaction during FTS. Non-significant sintering was observed with the exception of a few larger Fe particles present in the big zeolite cavity. Further analysis of this catalyst shall provide insights into the sites responsible for CO2 production, paving the way to a rational design of iron-based FTS catalysts

Interaction of titanium with smectite within the scope of a spent fuel repository: a spectroscopic approach

AbstractThe Swedish and Finnish nuclear waste repository design, KBS-3H, foresees horizontal emplacement of copper canisters-bentonite modules surrounded by a titanium shell. The interaction of titanium with bentonite was studied here using a combination of wet chemistry and a spectroscopic approach to evaluate the potential impact of Ti corrosion on the clay. For natural analogue clays with high Ti contents, spectroscopic investigations showed that titanium occurs as crystalline TiO2. In contrast, the Ti in the MX-80 bentonite occurs in the clay structure, presumably in the octahedral sheet. Hydrothermal tests conducted at 200°C using synthetic montmorillonite showed little if any change in the montmorillonite structure at near-neutral and acidic conditions. Under alkaline conditions, limited alteration was observed, including the formation of trioctahedral clay minerals and zeolite. These changes, however, occurred independently of the addition of Ti. In the batch tests conducted at 80°C, Ti did not occur as separate TiO2particles. The comparison of experimental data with spectroscopic simulations provides sound evidence that Ti was incorporated in a neoformed phyllosilicate structure.</jats:p

Synthesis and Study of a Ce-Doped La/Sr Titanate for Solid Oxide Fuel Cell Anode Operating Directly on Methane

6 Perillat-Merceroz, Cedric Gauthier, Gilles Roussel, Pascal Huve, Marielle Gelin, Patrick Vannier, Rose-NoelleThe possibility to introduce cerium in the perovskite-type titanate with formula La0.33Sr0.67TiO3+delta (LST) was investigated. Pure-phased La0.23Ce0.1Sr0.67TiO3+delta (LCST) was only obtained by synthesis at high temperature in reducing (diluted hydrogen) atmosphere. The material exhibits the same orthorhombic symmetry with Immm space group as LST and nearly the same cell volume. When exposed to oxidizing atmosphere at 1200 degrees C, Ti3+ and Ce3+ oxidation leads to the decomposition of LCST and the growth of several nanoscaled Ce-rich phases, as highlighted by backscattered electron microscopy. Shifting the gas back to a reducing atmosphere, but at lower temperature, only involves partial reversibility, ensuring the presence of nanoparticles of (electro)catalytically active phase within an electronically conducting n-type network. The catalytic tests in methane steam reforming at 900 degrees C (CH4/H2O = 10/1) show that the properties of the partially decomposed phase are greatly improved, what could make it a promising anode material for SOFC operating on slightly wet methane

Microstructural investigations and nanoscale ferroelectric properties in lead-free Nd2Ti2O7 thin films grown on SrTiO3 substrates by pulsed laser deposition

The growth conditions required to obtain high-quality layered-perovskite Nd2Ti2O7 thin films with a monoclinic structure on both (100)- and (110)-oriented SrTiO3 substrates by pulsed laser deposition are investigated. To synthesize the expected ferroelectric crystalline phase (and optimize the crystallization), two major critical parameters have to be carefully controlled, i.e. the oxygen pressure during deposition and the substrate temperature. Combining X-ray diffraction and transmission electron microscopy for structural characterizations, a twinned structure with (00l) orientation is evidenced for the films grown on (110)-oriented SrTiO3 while a twinned structure with a (012) orientation slightly tilted from 3.6u with respect to the substrate plane is revealed in the case of (100)-oriented SrTiO3. For growth performed at very low pressure, NdTiO3+delta thin films are obtained while polymorphic non-ferroelectric Nd2Ti2O7 samples with an orthorhombic structure are found at higher pressures. Piezoresponse force microscopy experiments evidence nanoscale ferroelectricity in the layered-perovskite monoclinic Nd2Ti2O7 films deposited on both substrates. Domain switching properties are shown to be more reliable for films grown onto (110)-SrTiO3 substrates, demonstrating these are more suitable as a functional material for applications in the field of micro-/nano-electronics. On the other hand, no ferroelectricity is probed in the polymorphic Nd2Ti2O7 thin films, as expected in a centro-symmetric structure