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 γ-alumina

SSCI-VIDE+ECI2D:ING+DEC:FMO:JRO:PAF:LPINational audienceIn this work, the stability of γ-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/γ-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 γ-alumina

SSCI-VIDE+ECI2D:ING+DEC:FMO:JRO:PAF:LPINational audienceIn this work, the stability of γ-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/γ-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 γ-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 γ-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_<i>n</i> clusters (<i>n</i> ≤ 13) interacting with four relevant γ-alumina surfaces exhibiting various hydroxylation and chlorination states. The presence of chlorine on the (110) surface of γ-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_<i>n</i> cluster with the available Al_III site, associated with strong H–Pt_<i>n</i>–Cl interaction. In particular, this trend leads to a local energy minimum, as a function of cluster size, for the Pt₃ 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