Valérie Caps

Catalytic oxidation of light alkanes (C1-C4) by heteropoly compounds.

(C1−C4) by Heteropoly Compounds Miao Sun,*,† Jizhe Zhang,‡ Piotr Putaj, Valerie Caps, Fred́eŕic Lefebvre, Jeremie Pelletier, and Jean-Marie Basset* †Research and Development Center, Saudi Aramco Oil Company, Dhahran 31311, Saudi Arabia ‡Division of Chemical and Life Sciences and Engineering, and KAUST Catalysis Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Laboratoire de Chimie Organomet́allique de Surface, CPE Lyon, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne, France

Gold Nanoparticles Supported on Passivated Silica: Access to an Efficient Aerobic Epoxidation Catalyst and the Intrinsic Oxidation Activity of Gold

Well-defined and perfectly dispersed [( identical withSiO)Au(I)] surface species supported on silica have been obtained via surface organometallic chemistry and transformed upon mild reduction (H(2), 300 degrees C) into small (1.8 +/- 0.6 nm) Au particles supported on silica passivated with SiMe(3) functionalities. Improved performance in liquid-phase aerobic epoxidation has been achieved, and the intrinsic activity of gold in oxidation is revealed.

Stereoselective stilbene epoxidation over supported gold-based catalysts

The gold reference catalyst Au/TiO(2) exhibits high activity in the stereoselective epoxidation of trans-stilbene in methylcyclohexane in the presence of 5 mol% TBHP, by taking part in a chain reaction involving the activation of molecular oxygen by a radical produced from methylcyclohexane.

Aerobic methylcyclohexane-promoted epoxidation of stilbene over gold nanoparticles supported on Gd-doped titania

Aerobic partial oxidations of alkanes and alkenes are important processes of the petrochemical industry. The radical mechanisms involved can be catalyzed by soluble salts of transition metals (Co, Cu, Mn...). We show here that the model methylcyclohexane/stilbene co-oxidation reaction can be efficiently catalyzed at lower temperature by supported gold nanoparticles. The support has little influence on gold intrinsic activity but more on the apparent reaction rates which are a combination of catalytic activity and diffusion limitations. These are here minimized by using gadolinium-doped titania nanocrystallites as support for gold nanoparticles. This material is obtained by mild hydrolysis of a new Gd(4)TiO(O(i)Pr)(14) bimetallic oxoalkoxide. It leads to enhanced wettability of the < 3 nm gold particles in the tert-butyl hydroperoxide (TBHP)-initiated epoxidation of stilbene in methylcyclohexane; Au/TiO(2):Gd(3+) is in turn as active as the state-of-the-art hydrophobic Au/SiO(2) catalyst. The rate-determining step of this reaction is identified as the gold-catalyzed homolytic decomposition of TBHP generating radicals and initiating the methylcyclohexane-mediated epoxidation of stilbene, yielding a methylcyclohexan-1-ol/trans-stilbene oxide mixture. Methylcyclohexan-1-ol can also be obtained in the absence of the alkene in the gold-catalyzed solvent-free autoxidation of methylcyclohexane, evidencing the catalytic potential of gold nanoparticles for low temperature C-H activation.

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.

Methane Reacts with Heteropolyacids Chemisorbed on Silica to Produce Acetic Acid under Soft Conditions

Selective functionalization of methane at moderate temperature is of crucial economic, environmental, and scientific importance. Here, we report that methane reacts with heteropolyacids (HPAs) chemisorbed on silica to produce acetic acid under soft conditions. Specially, when chemisorbed on silica, H(4)SiW(12)O(40), H(3)PW(12)O(40), H(4)SiMo(12)O(40), and H(3)PMo(12)O(40) activate the primary C-H bond of methane at room temperature and atmospheric pressure. With these systems, acetic acid is produced directly from methane, in a single step, in the absence of Pd and without adding CO. Extensive surface characterization by solid-state NMR spectroscopy, IR spectroscopy, cyclic voltammetry, and X-ray photoelectron spectroscopy suggests that C-H activation of methane is triggered by the protons in the HPA-silica interface with concerted reduction of the Keggin cage, leading to water formation and hydration of the interface. This is the simplest and mildest way reported to date to functionalize methane.

Effect of the titania morphology on the preparation of Au/TiO2(/SiO2) catalysts

Abstract The deposition-precipitation method is applied to pure anatase titanias with high surface areas and silica mesostructures doped with Ti/TiO 2 . The effect of the type and density of surface functionalities both on the deposition of gold and on the catalytic properties of the resulting materials in the oxidation of CO in the presence of H 2 are discussed.

Single‐Phase Heterogeneous Pt3Sn Catalyst Synthesized by Room‐Temperature Self‐Assembly

The facile and reproducible preparation of a well-defined bimetallic Pt3Sn catalyst that contained evenly distributed 2.4 nm Pt3Sn-alloy nanoparticles along its channel pores was performed in quantitative yield by the controlled growth of a mesostructured silica matrix around the preformed Pt3Sn nanoparticles. The material was fully characterized and was found to be very selective in the classical isobutane-dehydrogenation reaction and very active in the low-temperature preferential oxidation of CO in the presence of H2 (PROX reaction). Bimetallic Pt X heterogeneous catalysts are widely used in the petrochemical industry and are finding increasing application in fuel-cell technology. The platinum tin catalysts that are used in reforming processes display superior selectivities and -lifetimes to their monometallic Pt counterparts. 2] However, these bimetallic catalysts are typically ill-defined and contain various Ptx Sn phases because their preparation typically involves high-temperature treatments. Therefore, it is difficult to determine clear “structure–activity” relationships and, thus, to develop rational approaches to improve the catalysts in this field. In fuel-cell (FC) technology, bimetallic Pt Sn systems are emerging as more-CO-tolerant electrocatalysts during the anodic oxidation of H2 [3, 4] and are particularly promising for proton-exchange-membrane (PEM) FCs as PROX catalysts for the purification of fuel-cell upstream gaseous-H2 feedstocks. [6–9] The nature of the active sites on the bimetallic Pt Sn systems, as well as the mechanism for the PROX catalysis, are still not known, but computational studies (DFT) have suggested that the Pt3Sn alloy (and solely this specific alloy out of all possible Ptx Sn combinations) is able to catalyze the oxidation of CO at lower temperatures than the reference monometallic Pt/ Al2O3 catalyst. [11] Herein, we report the facileand undisruptive incorporation of well-defined bimetallic Pt3Sn-alloy particles [12] into the channel pores of mesostructured silica. This incorporation into solid matrices permits applications of the single-phase Pt3Sn nanoparticles in heterogeneous catalysis, which is not possible with the original colloidal solution. After characterization of this new material, its catalytic performance in the dehydrogenation of isobutane and in PROX reactions will be reported. The controlled growth of the silica matrix around the Pt3Sn colloids was achieved by using an emerging route in materials chemistry, termed a “supramolecular pathway”, which consisted of the hydrolysis/condensation of a silica precursor around structure-directing agents in the presence of preformed nanoparticles (NPs) within the mesophase. This hydrolytic sol– gel route was preferred to other classical procedures (e.g. , impregnation and salt-decomposition) to secure a regular distribution of the metallic nanoparticles inside the pore channels, as recently demonstrated for mesostructured silica that contained 3 nm Pt NPs in the pores of the silica matrix (Pt@SiO2). [15] Herein, the mesostructured matrix was synthesized by the addition of a preformed solution of Pt3Sn colloids [12] to an aqueous solution of Pluronic P123 that contained NaF. After the evacuation of THF, an acidic solution of tetraethoxysilane was added and the resulting mixture was stirred for a further 24 h at 35 8C to yield the crude material as a gray solid (Pt3Sn@SiO2-crude), which was further calcined at 593 K to yield the final material, Pt3Sn@SiO2. Pt3Sn@SiO2 is a highly structured material with 2D hexagonal long-range ordering of the pore channels and a mean pore-diameter of about 7 nm, as shown in the TEM micrographs (Figure 1). The superior physical structuration of the solid porous network was also visible in the small-angle X-ray diffraction patterns (see the Supporting Information, Figure S3), which exhibited one intense diffraction peak that correspond[a] Dr. M. Boualleg, Prof. J.-M. Basset, Dr. J.-P. Candy, Dr. S. Norsic, Dr. E. A. Quadrelli, L. Veyre, Dr. C. Thieuleux Universit de Lyon Institut de Chimie de Lyon UMR 5265CNRS Universit Lyon 1 ESCPE Lyon, LC2P2 Equipe Chimie Organom tallique de Surface 43 Bd du 11 Novembre 1918, 69616 Villeurbanne (France) E-mail : thieuleux@cpe.fr

One-Pot Synthesis of Size- and Composition-Controlled Ni-Rich NiPt Alloy Nanoparticles in a Reverse Microemulsion System and Their Application

Bimetallic nanoparticles have been the subject of numerous research studies in the nanotechnology field, in particular for catalytic applications. Control of the size, morphology, and composition has become a key challenge due to the relationship between these parameters and the catalytic behavior of the particles in terms of activity, selectivity, and stability. Here, we present a one-pot air synthesis of 2 nm Ni9Pt1 nanoparticles with a narrow size distribution. Control of the size and composition of the alloy particles is achieved at ambient temperature, in the aqueous phase, by the simultaneous reduction of nickel and platinum precursors with hydrazine, using a reverse microemulsion system. After deposition on an alumina support, this Ni-rich nanoalloy exhibits unprecedented stability under the harsh conditions of methane dry reforming.