Katrin Pelzer

Organized 3D-alkyl imidazolium ionic liquids could be used to control the size of in situ generated ruthenium nanoparticles?

The synthesis of ruthenium nanoparticles, RuNPs from the organometallic complex (η4-1,5-cyclooctadiene)(η6-1,3,5-cyclooctatriene)ruthenium(0), Ru(COD)(COT) in various imidazolium derived ionic liquids, ILs: [RMIm][NTf2] (R = CnH2n + 1 with n = 2; 4; 6; 8; 10), and [R2Im][NTf2] (RBu) and [BMMIm][NTf2] has been performed, under 0.4 MPa of H2, at 25 °C or at 0 °C with or without stirring. A relationship between the size of IL non-polar domains calculated by molecular dynamics simulation and the RuNP size measured by TEM has been found, suggesting that the phenomenon of crystal growth is probably controlled by the local concentration of Ru(COD)(COT) and consequently is limited to the size of the non-polar domains. Moreover, the rigid 3D organization based on C2–H⋯anion bonding and chosen experimental conditions, could explain the non-aggregation of RuNPs.

Mononuclear Ruthenium Hydride Species versus Ruthenium Nanoparticles: The Effect of Silane Functionalities on Silica Surfaces

The area of nanoparticle synthesis has gained interest in the past few years due to their potential and application in areas such as microelectronics and selective catalysis. In the case of metal nanoparticles, their properties are often related to their size and shape, and therefore controlling their growth has been an area of active research for decades. In the specific case of supported metal nanoparticles, some control is possible by changing the precursor, the method of impregnation, the nature of oxide support, and the final decomposition method. Using perhydrocarbyl complex precursors provides some advantages because of their ease of decomposition under H2, which leads to metal surfaces free of strong ligands such as CO or Cl . The particle mean size can be somewhat controlled by the choice of the support, which directs the migration of the zero-valent ensembles in the process of the crystal growth, but the resulting particles are usually large (>1 nm). Even if the organometallic precursor is first grafted to the support to ensure a high dispersion, treatment under H2 at high temperatures leads to the cleavage of the M O bond and to aggregation, yielding large supported metal particles. Controlling or even avoiding the aggregation process on oxide supports by surface organometallic chemistry tools would lead to smaller nanoparticles of a few atoms (<1 nm) or analogues of the early transition-metal surface hydrides, which could be of great interest for catalytic applications. Recently, Pelzer et al. have shown that the treatment of a pentane solution of [RuACHTUNGTRENNUNG(cod) ACHTUNGTRENNUNG(cot)] (cod=cyclooctadiene, cot=cyclooctatriene) under 3 bars of H2 in the presence of octylsilane yields soluble 2-nm nanoparticles stabilized by direct Ru Si bonds. Here, we show that tuning silica by adding surface Si H bonds generates a support that avoids aggregation of the metal during the treatment under H2 at high temperatures of grafted [Ru ACHTUNGTRENNUNG(cod)ACHTUNGTRENNUNG(cot)], yielding stable silica-supported mononuclear ruthenium hydride species ACHTUNGTRENNUNG[Ru-H] (Scheme 1). This system will be compared with what is usually obtained on silica support, namely Ru nanoparticles, RuP/SiO2. [6] The solid ACHTUNGTRENNUNG[Ru-H] is typically prepared by treatment under H2 (2055 equiv) at 300 8C for 24 h of solid ACHTUNGTRENNUNG[Ru-L] obtained by reaction of [Ru ACHTUNGTRENNUNG(cod) ACHTUNGTRENNUNG(cot)] (0.3–0.6 equiv/SiH) with a silica covered with surface silanes, [( SiO)SiMe2H] (0.24 mmol per g or ca. 0.7 SiH per nm). During the treatment under H2 at 300 8C, about 10 1 equivalents of CH4/ Ru are formed, in agreement with the hydrogenolysis of some hydrocarbon species. TEM analysis on the resulting light brown solid ACHTUNGTRENNUNG[Ru-H] does not show the presence of Ru particles, even for 0.85 wt% Ru loading (see Figure S1 in the Supporting Information). This is in sharp contrast with what is obtained by treating [Ru ACHTUNGTRENNUNG(cod) ACHTUNGTRENNUNG(cot)] adsorbed on silica under H2 at 300 8C, which affords homogeneously dispersed Ru particles, RuP/SiO2 (0.73 wt%), with a mean size of 2.1 0.3 nm (see Figure S2 and S3 in the Supporting Information). In fact, while [Ru ACHTUNGTRENNUNG(cod) ACHTUNGTRENNUNG(cot)] is only physisorbed on silica (SiO2 (700), ca. 0.7 OH per nm ) and can be removed by simple washing with pentane, [Ru ACHTUNGTRENNUNG(cod) ACHTUNGTRENNUNG(cot)] reacts with [( SiO)SiMe2H] (1.65 equiv) as evidenced by the disappearance of the yellow color of the solution during impregnation to yield an orange-brown solid ACHTUNGTRENNUNG[Ru-L] . This solid contains 1.52wt% of Ru, that is 0.15 mmol of Ru per g of solid, in agreement with the grafting of all the [Ru ACHTUNGTRENNUNG(cod) ACHTUNGTRENNUNG(cot)] loaded. [a] R. Berthoud, A. Baudouin, Dr. J.-M. Basset, Dr. J.-P. Candy, Dr. C. Cop=ret Universit= de Lyon, Institut de Chimie de Lyon, C2P2 LCOMS ESCPE Lyon, 43, Bd. du 11 Novembre 69616 Villeurbanne (France) Fax: (+33)472431795 E-mail : coperet@cpe.fr [b] Dr. B. Fenet Centre de RMN, Universit= Lyon 1 Claude Bernard, ESCPE Lyon, 43, Bd du 11 Novembre, 69616 Villeurbanne Cedex (France) [c] Dr. W. Lukens Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (USA) [d] Dr. K. Pelzer Department for Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, 14195 Berlin (Germany) Supporting information for this article is available on the WWW under http://www.chemistry.org or from the author.

2H-solid-state-NMR study of hydrogen adsorbed on catalytically active ruthenium coated mesoporous silica materials

(2)H solid-state NMR measurements were performed on three samples of ruthenium nanoparticles synthesized inside two different kinds of mesoporous silica, namely SBA-3 silica materials and SBA-15 functionalized with -COOH groups and loaded with deuterium gas. The line-shape analyses of the spectra reveal the different deuteron species. In all samples a strong -OD signal is found, which shows the catalytic activity of the metal, which activates the D-D bond and deuterates the -SiOH groups through the gas phase, corroborating their usability as catalysts for hydrogenation reactions. At room temperature the mobility of the -Si-OD groups depends on the sample preparation. In addition to the -Si-OD deuterons, the presence of different types of deuterons bound to the metal is revealed. The singly coordinated -Ru-D species exhibit several different quadrupolar couplings, which indicate the presence of several non-equivalent binding sites with differing binding strength. In addition to the dissociated hydrogen species there is also a dihydrogen species -Ru-D(2), which is attributed to defect sites on the surface. It exhibits a fast rotational dynamics at all temperatures. Finally there are also indications of three-fold coordinated surface deuterons and octahedrally coordinated deuterons inside the metal.

Molecular beam mass spectrometer equipped with a catalytic wall reactor for in situ studies in high temperature catalysis research

A newly developed apparatus combining a molecular beam mass spectrometer and a catalytic wall reactor is described. The setup has been developed for in situ studies of high temperature catalytic reactions (>1000°C), which involve besides surface reactions also gas phase reactions in their mechanism. The goal is to identify gas phase radicals by threshold ionization. A tubular reactor, made from the catalytic material, is positioned in a vacuum chamber. Expansion of the gas through a 100μm sampling orifice in the reactor wall into differentially pumped nozzle, skimmer, and collimator chambers leads to the formation of a molecular beam. A quadrupole mass spectrometer with electron impact ion source designed for molecular beam inlet and threshold ionization measurements is used as the analyzer. The sampling time from nozzle to detector is estimated to be less than 10ms. A detection time resolution of up to 20ms can be reached. The temperature of the reactor is measured by pyrometry. Besides a detailed descri...