Gérard Bergeret

Guest-induced gate-opening of a zeolite imidazolate framework

The zinc benzimidazolate coordination polymer (ZIF-7) shows a reversible gate-opening effect upon variation of partial pressure of CO2 or temperature. This phenomenon, which is unique for a MOF with sodalite topology, arises from a phase-to-phase transformation upon guest adsorption–desorption.

Absolute molecular sieve separation of ethylene/ethane mixtures with silver zeolite A.

Absolute ethylene/ethane separation is achieved by ethane exclusion on silver-exchanged zeolite A adsorbent. This molecular sieving type separation is attributed to the pore size of the adsorbent, which falls between ethylene and ethane kinetic diameters.

Homogeneity of flexible metal–organic frameworks containing mixed linkers

Very sophisticated porous materials known as multivariate functional MOFs (also known as MixMOFs) can be designed using a synthesis method that starts from solutions composed of two or more different linkers. For this procedure to be successful, one must have access to techniques that characterize the homogeneity of MOF crystallites containing two different linkers. This is of particular relevance for MOFs made of 2-aminobenzene-1,4-dicarboxylate (abdc), which are excellent platforms for the introduction of additional functions by post-modification. In this paper, we show that adsorption/desorption isotherms and thermodiffraction studies on flexible structures can indirectly characterize the homogeneity of MOFs made from a mixture of linkers. Breathing pressures and temperatures for a series of MIL-53(Al) functionalized with amino tags, i.e. Al(OH)(bdc)1−n(abdc)n, were measured as a function of the amino content. The linear relationship between the CO2 breathing pressure and the amine content in the MIL-53(Al) structure clearly illustrates the homogeneity of the crystallite composition; in other words, the crystallites have the same abdc : bdc ratio. On the other hand, the functionalization of MIL-53(Al) with low amine content (10% abdc) results in a profound modification of the breathing properties triggered by the temperature. Much higher temperatures are required for full conversion of the np (narrow pore) to the lp (large pore) phase. We also suggest an interplay between coexisting np and lp microcrystalline domains that may “smooth” the breathing properties at the macroscopic level.

Structures and associated catalytic properties of well-defined nanoparticles produced by laser vaporisation of alloy rods

Bimetallic clusters, all containing gold, have been produced by laser vaporisation of bulk alloys followed by deposition of the formed clusters onto Al2O3 and TiO2 powders or flat silica supports. This technique allows a narrow size distribution of highly dispersed gold-based nanoparticles on powders and nanocrystalline structured thin films on 2D supports to be obtained. The catalytic performances of the as-obtained AuFe, AuNi, AuTi powdery catalysts have been studied in the PROX reaction and compared with those obtained in the oxidation of CO in the temperature range 25-300 degrees C. By comparing the activities of the different catalysts, it is concluded that the nature of the gold partner directly affects the activity of gold. The following tendency is observed: AuFe and AuNi have rather similar activities, significantly lower than that of AuTi. In this paper, we also present a first attempt to study reactivity of original self-supported systems. We show that significant CO oxidation reactivity can be obtained over unsupported nanoporous AuTi and PdAu thin films. By completely excluding the support effect, unsupported catalysts could provide a way of understanding the relevant catalytic mechanisms more easily.

Functionalized gold magic clusters: Au25(SPhNH2)17

New Au(25) nanoclusters stabilized by heterotopic 4-aminothiophenolate ligands (HSPhNH(2)) have been isolated with a yield of ~70%. The nanoclusters formula determined by ESI-MS is Au(25)(SPhNH(2))(17), with the 18(th) position occupied by an amine or DMF molecules to close their electronic shell.

Operando study of iridium acetylacetonate decomposition on amorphous silica–alumina for bifunctional catalyst preparation

The decomposition of iridium acetylacetonate Ir(acac)(3) impregnated on amorphous silica-alumina (ASA) has been investigated by combined thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) and by in situ X-ray diffraction (XRD). The resulting Ir/ASA hydrotreating catalysts have also been characterized by transmission electron microscopy (TEM). The effects of heating treatments under oxidative, reductive or inert gas flows are compared with each other and with similar experiments on ASA-supported acetylacetone (acacH). It is shown that Ir(acac)(3) undergoes exothermic combustion during calcination in air, leading to agglomerated IrO(2) particles. Conversely, direct reduction involves hydrogenolysis of the acac followed by hydrogenation of the ligand residues to alkanes and water. These two processes are catalyzed by Ir clusters, the gradual growth of which is followed in situ by XRD. The resulting nanoparticles are highly and homogeneously dispersed.

Cinnamaldehyde hydrogenation: Dual catalytic chemistry of iron-rhodium/Grafoil catalysts

Abstract Work in our laboratory has shown that may bimetallic particles, including Fe/Rh, Fe/ Ir and Pd/Ag, have multiple phase structures that can be accessed through the proper sequence of treatments. Corresponding to the multiple bulk phase structures are a variety of surface structures and compositions. In this study it is shown for Fe/Rh that the different surfaces have completely different selectivities for cinnamaldehyde hydrogenation. Moreover, it is clear that the catalytic behavior of the alloy is not a simple linear combination of the behaviors observed for the parent metals, indicating that alloys may prove to have unique properties for low-temperature selective hydrogenations.

Preparation of nanosized bimetallic Ni-Sn and Ni-Au/SiO2 catalysts by SOMC/M. Correlation between structure and catalytic properties in styrene hydrogenation

Abstract The aim of this study is to prepare silica-supported Ni-X bimetallic catalysts, to characterize them and to compare their catalytic activity in the hydrogenation of styrene, as well as their selectivity in the hydrogenation of the styrenes olefinic double bond instead of the hydrogenation of the aromatic ring. The element X is grafted in a controlled way on the supported nickel particles, and is chosen according to its electronegativity, which is either equivalent (Sn) or higher (Au) than the electronegativity of Ni, in order to study the geometrical and/or electronic effects due to the doping of nickel. Among the prepared samples, the Ni-Au/SiO 2 catalyst has exhibited high activity and high selectivity in the hydrogenation of styrene into ethylbenzene, suggesting that a combination of geometric and electro-attractor effects are involved.