Dorothée Berthomieu

Selective Catalytic Reduction of NO by NH3 on Cu-Faujasite Catalysts: An Experimental and Quantum Chemical Approach

The selective catalytic reduction (SCR) of NO by NH3 in the presence of O2 on Cu-faujasite (Cu-FAU) has been studied. Substitution of some Cu2+ with H+ and Na+ cations, compensating for the negative charge of the zeolite framework, forms the various CuHNa-FAU studied. The amount of Cu was held constant and the proportion of H+ and Na+ varied in the sample. The substitution of Na+ for H+ increases sharply the SCR rate by lowering the temperature of reaction by about 150 K. It is proposed that the rate increase mainly comes from an unhindered migration of Cu from hidden to active sites and a modification of the redox properties of Cu species. The former was demonstrated by diffuse reflectance IR spectroscopy of adsorbed CO. The change in redox properties was demonstrated by a faster oxidation of Cu+ to Cu2+ (rate-determining step). Quantum chemical calculations on model clusters of CuHNa-FAU indicate that the faster rate of oxidation can be explained by a higher lability of protons in the absence of Na, which can be then removed from the catalyst more easily to yield H2O during the oxidation process.

Intermediate Complexes in the Gas-Phase Reaction of the Tert-C4H9+ Cation with Water

Both ion cyclotron resonance (ICR) and mass-analyzed ion kinetic energy (MIKE) experiments indicate that a slow H/D exchange occurs when the tert-C4H9+ cation reacts with D2O. This can be rationalized by the interconversion between [tert-C4H9+, H2O] and [isobutene, H3O+] complexes. Semi-empirical calculations show that the [tert-C4H9+, H2O] complexes clearly correspond to several minima on the potential energy surface (PES). The most stable of these complexes is also found to be an energy minimum by ab initio calculations. The corresponding structure is highly stabilized. Its interaction energy is 44.4 kJ mol−1 calculated by the G2(MP2,SVP) method. In contrast, it depends on the calculation method whether the [isobutene, H3O+] complex is found to have an energy minimum on the PES or not. This area of the PES is rather flat and probably corresponds to a plateau or to a broad transition state allowing isomerization of the α-complex with H-permutation. Since this plateau has an energy value very near the [tert-C4H9+, H2O] final state, the β-structure [isobutene, H3O+] can operate in the H/D exchange reaction but is rate limiting in this process.

Multiple adsorption of CO on Na-exchanged Y faujasite: a DFT investigation

Carbon monoxide is involved in many chemical and industrial processes, and its removal is of great importance to reduce detrimental environmental and climate impacts. CO is also useful to characterise the metal exchanged in zeolites. Multiple adsorption of CO in zeolite faujasites containing Na cations is investigated through quantum chemical calculations. Density functional theory (DFT) calculations were chosen to investigate the structure of sodium-exchanged cations at site II in Y faujasite and to investigate multiple CO adsorption with Na to predict the structure and the infrared CO stretching signal. DFT analysis using B3LYP, B3LYP-D and M062X showed significant differences in the coordination of Na at site II when three CO are adsorbed. From these investigations, polyadsorption of CO in NaY could lead to threefold-coordinated Na at site II in six-membered rings (6MRs) containing two Al and twofold-coordinated Na at site II in 6MRs containing one Al. These results suggest that introduction of non-bonding interactions is necessary to study polyadsorption of CO in NaY.

Profiling the Active Site of a Copper Enzyme through Its Far‐Infrared Fingerprint

Vibrations of the metal active site of the Cu,Zn-superoxide dismutase enzyme were analyzed by far-infrared difference spectroscopy and theoretical normal mode calculation. Both electrochemically triggered Cu(I) and Cu(II) redox states show well-defined infrared vibrational modes, notably modes of the histidine ligands, the Cu(II)-His(61)-Zn(II) bridge and of the water pseudo-ligand.

N2O decomposition over (μ-oxo)(μ-hydroxo)di-iron complex supported by ZSM-5 zeolite: effect of cluster size on DFT energy profile

Abstract Elementary reaction mechanisms for nitrous oxide (N 2 O) dissociation were studied on [Fen II (μ-O)(μ-OH)Fe II ] + exchanged in ZSM-5, using density functional theory (DFT). The effect of the cluster size on the energetics and on the reaction routes of N 2 O dissociation were investigated over di-iron core inserted inside two different Z cluster (Z − ) and (Z − OH ). The results show that while the relative stability changes with the cluster termination, the height of the energetic barriers are similar.

Density functional theory modelling EPR spectra of Cu(II) in Y zeolite

Electron paramgnetic resonance (EPR) experiments have shown that Cu(II) occupy different positions in the Y zeolite. We have studied the EPR properties of different cluster models in which copper is located at different cristallographic sites and different positions. The calculated results showed that the unpaired electron of copper is delocalized on the zeolite and that the hyperfine coupling constants depend linearly on the spin density of the models whatever are the structures and the calculation methods. These calculated constant values are close to experimental values when Cu(II) occupy ideal positions, ie. when it is four-coordinated at the center of a four or six-membered ring.

Reactions of H−, D− and HD− transfer between an ethylene cation and propane CH3CD2CH3: a study of kinetics using state-selected reactants

Abstract The dependence on the reactant collisional and internal energy of the total cross sections of hydride-ion (H − or D − ) and HD − transfer reactions in the system C 2 D 4 + + CH 3 CD 2 CH 3 was investigated using vibrationally state-selected reactant ions and guided-beam techniques. The cross sections of formation of C 3 D 6 H + (D − abstraction from position 2 of the target molecule) and C 3 H 5 D + (HD − abstraction from positions 1 and 2) decreased with both collision and reactant ion internal energy as it is usual for exoergic processes. Formation of C 3 H 5 D 2 + (H − abstraction from position 1) exhibited a much smaller cross section raising from a threshold near the energy zero, suggesting a slightly endoergic process, in agreement with thermochemical calculations. The internal energy appears to be about 4 x more effective than the translational energy in overcoming the endoergicity barrier of this process.

Molecular dynamics simulations of H2O with sites of CuI-FAU and CuII-FAU

A Born Oppenheimer molecular dynamic (BOMD) approach was chosen to study the interaction of water molecules with Cu-FAU models. We have compared the reactivity of Cu I and Cu II with the zeolite and compared the results to those calculated for Na. This study shows a decrease of the coordination with time for Cu I whereas there is not a significant change for Cu II . BOMD shows also that, in the presence of water, Na + may lead to easier cation exchange than for transition metal cations.

Quantum Calculation for Musk Molecules Infrared Spectra towards the Understanding of Odor

It is not clear so far how humans can recognize odor. One of the theories regarding structure-odor relationship is vibrational theory, which claims that odors can be recognized by their modes of vibration. In this sense, this paper brings a novel comparison made between musky and nonmusky molecules, as to check the existence of correlation between their modes on the infrared spectra and odor. For this purpose, sixteen musky odorants were chosen, as well as seven other molecules that are structurally similar to them, but with no musk odor. All of them were submitted to solid theoretical methodology (using molecular mechanics/molecular dynamics and Neglect of Diatomic Differential Overlap Austin Model 1 methods to optimize geometries) as to achieve density functional theory spectra information, with both Gradient Corrected Functional Perdew-Wang generalized-gradient approximation (GGA/PW91) and hybrid Becke, three-parameter, Lee-Yang-Parr (B3LYP) functional. For a proper analysis over spectral data, a mathematical method was designed, generating weighted averages for theoretical frequencies and computing deviations from these averages. It was then devised that musky odorants satisfied demands of the vibrational theory, while nonmusk compounds belonging either to nitro group or to acyclic group failed to fulfill the same criteria.

Flavonol dye molecules in zeolite beta nanocrystals for biodiagnostic applications

Abstract Colloidal zeolite Beta nanocrystals with a Si/Al ratio of 18.5 were prepared via mild hydrothermal synthesis. The zeolite Beta nanoparticles were highly uniform in size, had a mean diameter of 100 nm, built with nanosized crystals and exhibited both micro- and mesoporosity. A calcination treatment was developed to produce template-free zeolite Beta nanocrystals with sizes and crystalline structure similar to the original zeolite Beta nanoparticles. Flavonol dye molecules were loaded in the calcinated zeolite Beta nanoparticles. Zeolite Beta nanoparticles were characterized extensively at each step of the process by complementary techniques such as X-ray diffraction, scanning electron microscopy, dynamic light scattering, nitrogen sorption, elemental analysis, static fluorescence and Raman analysis. A comprehensive study of the structure-photophysical property relations of the dye loaded zeolite Beta nanoparticles is presented