103 research outputs found
Metal/Acid Bifunctional Catalysis and Intimacy Criterion for Ethylcyclohexane Hydroconversion: When Proximity Does Not Matter
SSCI-VIDE+ING+YSCInternational audiencebifunctional catalys
Bifunctional catalysis and intimacy criterion: industrial application for hydrocracking and hydroisomerization
SSCI-VIDE+ING+YSCInternational audienceBifunctional catalysts consisting of a noble metal with an hydrogenation/ dehydrogenation (HD/DHD) function and an acidic function, generally a zeolite, are used in several processes of refining and petrochemical industries. Two criteria define the catalytic properties of a bifunctional catalysts: the balance between HD/DHD and an acidic function and the proximity between both functions. When the catalyst is well balanced, the hydro/dehydrogenation reactions are at quasi equilibrium and the limiting step of the reaction takes place on the acidic function . The bifunctional catalyst activity and selectivity depend essentially on acidity and pore structure of the acid soli
Sulfur Deactivation of NOx Storage Catalysts: A Multiscale Modeling Approach
Lean NOx Trap (LNT) catalysts, a promising solution for
reducing the noxious nitrogen oxide emissions from the lean burn and Diesel engines, are
technologically limited by the presence of sulfur in the exhaust gas stream. Sulfur
stemming from both fuels and lubricating oils is oxidized during the combustion event and
mainly exists as SOx (SO2 and SO3) in
the exhaust. Sulfur oxides interact strongly with the NOx
trapping material of a LNT to form thermodynamically favored sulfate species, consequently
leading to the blockage of NOx sorption sites and altering the
catalyst operation. Molecular and kinetic modeling represent a valuable tool for
predicting system behavior and evaluating catalytic performances. The present paper
demonstrates how fundamental ab initio calculations can be used as a valuable source for
designing kinetic models developed in the IFP Exhaust library, intended for vehicle
simulations. The concrete example we chose to illustrate our approach was SO3
adsorption on the model NOx storage material, BaO.
SO3 adsorption was described for various sites (terraces, surface steps and
kinks and bulk) for a closer description of a real storage material. Additional rate and
sensitivity analyses provided a deeper understanding of the poisoning phenomena
Impact de l’état d’oxydation du platine sur l’oxydation catalytique du CO : Apport de la méthodologie SSITKA-IR
National audienc
Atmosphere-dependent stability, mobility and CO oxidation performance of Pt single atoms and clusters on Îł-alumina
SSCI-VIDE+ECI2D:ING+DEC:FMO:JRO:PAF:LPINational audienceIn this work, the stability of Îł-alumina-supported single Pt atoms formed by oxidative treatment of an impregnated Pt precursor has been monitored by operando X-ray absorption spectroscopy (XAS). Their destabilization into subnanometric clusters under reductive treatment has been studied by XAS and environmental scanning transmission electron microscopy (E-STEM). DFT calculations allow us to fully rationalize these behaviors in terms of nuclearity and adsorbate coverage (O or H), which governs the cluster size, shape and interaction with the support.Pt/Îł-Al2O3 SACs were also submitted to CO oxidation heating/cooling cycles separated by a reduction treatment and the catalysts were analyzed by operando DRIFTS, operando XAS and STEM
Atmosphere-dependent stability, mobility and CO oxidation performance of Pt single atoms and clusters on Îł-alumina
SSCI-VIDE+ECI2D:ING+DEC:FMO:JRO:PAF:LPINational audienceIn this work, the stability of Îł-alumina-supported single Pt atoms formed by oxidative treatment of an impregnated Pt precursor has been monitored by operando X-ray absorption spectroscopy (XAS). Their destabilization into subnanometric clusters under reductive treatment has been studied by XAS and environmental scanning transmission electron microscopy (E-STEM). DFT calculations allow us to fully rationalize these behaviors in terms of nuclearity and adsorbate coverage (O or H), which governs the cluster size, shape and interaction with the support.Pt/Îł-Al2O3 SACs were also submitted to CO oxidation heating/cooling cycles separated by a reduction treatment and the catalysts were analyzed by operando DRIFTS, operando XAS and STEM
Platinum Nanoclusters Stabilized on Îł-Alumina by Chlorine Used As a Capping Surface Ligand: A Density Functional Theory Study
Controlling the size of metallic nanoclusters supported
on an oxide
support such as Îł-alumina represents a challenging but important
task in the case of noble metals such as platinum. By using density
functional theory (DFT), we investigate the thermodynamic, structural
and electronic properties of small nanometer-sized Pt<sub><i>n</i></sub> clusters (<i>n</i> ≤ 13) interacting
with four relevant Îł-alumina surfaces exhibiting various hydroxylation
and chlorination states. The presence of chlorine on the (110) surface
of Îł-alumina implies a thermodynamic stabilization of small
platinum clusters. This stabilization originates from the simultaneous
migrations of chlorine atoms and protons from the support toward the
Pt clusters. The migration of H and Cl from the support induces a
stronger interaction of the Pt<sub><i>n</i></sub> cluster
with the available Al<sub>III</sub> site, associated with strong H–Pt<sub><i>n</i></sub>–Cl interaction. In particular, this
trend leads to a local energy minimum, as a function of cluster size,
for the Pt<sub>3</sub> cluster. This atomic-scale stabilization of
subnanometer clusters is thus proposed to be at the origin of the
formation of highly dispersed platinum particles and to prevent their
sintering into supranano ones. A detailed energetic and electronic
analysis is provided to rationalize this effect of chlorine. A rational
interpretation of experimental data is finally given
Copper Coordination to Water and Ammonia in Cu II -Exchanged SSZ-13: Atomistic Insights from DFT Calculations and in Situ XAS Experiments
International audienceIn this study, the coordination sphere of copper in Cu–SSZ-13 as a catalyst for the selective catalytic reduction of NOx by ammonia is analyzed as a function of environmental parameters: temperature, partial pressure of water P(H2O), and partial pressure of ammonia P(NH3). By periodic density functional theory calculations, we obtain stability domains for variable loadings of water and ammonia (nH2O + mNH3 with (m + n ≤ 6)) close to CuII ions, which are located at 6-membered ring (6MR) or 8-membered ring (8MR) of the zeolitic structure. Ab initio calculations and thermodynamic investigations were performed to build phase diagrams, with vibrational analysis, so as to provide Gibbs free energy, G, values. Copper located in the 8MR appears to be more reactive toward H2O and NH3 adsorption than the one in the 6MR because of a lower coordination number of copper at 8MR in the absence of adsorbates. Depending on the operating conditions, structures containing adsorbed water and ammonia as ligands at the metal site can simultaneously be stabilized. The most widespread coordination number of CuII is 4 even at m + n > 4. The theoretical predictions were validated by in situ X-ray absorption spectroscopy, in dehydration conditions and in two gas atmospheres: dry He with P(NH3) = 10–3 bar (1000 ppm) and He with P(NH3) = 10–3 bar and P(H2O) = 10–2 bar. Trends in terms of ammonia desorption temperature as well as coordination numbers are well reproduced. Experimentally determined behaviors of CuI and CuII open new perspectives for the systematic computational investigation of the behavior of CuI in a H2O/NH3 atmosphere
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