Philippe Serp

Carbon nanotubes and nanofibers in catalysis

This review analyses the literature from the early 1990s until the beginning of 2003 and covers the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports. The article is composed of three sections, the first one explains why these materials can be suitable for these applications, the second describes the different preparation methods for supporting metallic catalysts on these supports, and the last one details the catalytic results obtained with nanotubes or nanofibers based catalysts. When possible, the results were compared to those obtained on classical carbonaceous supports and explanations are proposed to clarify the different behaviors observed.

Parametric study for the growth of carbon nanotubes by catalytic chemical vapor deposition in a fluidized bed reactor

Multiwalled carbon nanotubes have been produced from H2–C2H4 mixtures on Fe–SiO2 catalysts by a fluidized bed catalytic chemical vapor deposition process. Various parameters such as the catalyst preparation, the residence time, the run duration, the temperature, the H2:C2H4 ratio, the amount of metal deposited on the support have been examined. The influence of these parameters on the deposited carbon yield is reported, together with observations of the produced material. This process allows an homogeneously distributed deposition of nanotubes (10–20 nm diameter), that remain anchored to the support.

Introduction to Carbon Nanotubes

Carbon nanotubes are remarkable objects that look set to revolutionize the technological landscape in the near future. Tomorrowʼs society will be shaped by nanotube applications, just as silicon-based technologies dominate society today. Space elevators tethered by the strongest of cables; hydrogen-powered vehicles; artificial muscles: these are just a few of the technological marvels that may be made possible by the emerging science of carbon nanotubes.

A Facile Route to Carbonylhalogenometal Complexes (M = Rh, Ir, Ru, Pt) by Dimethylformamide Decarbonylation

Dimethyl formamide (DMF) can be a convenient source of the carbonyl ligand in the coordination chemistry of rhodium, ruthenium, iridium, and platinum. We have undertaken a thorough study concerning the course of this reaction. In a first step, DMF-containing complexes are produced, which is usually accompanied by chloride redistribution. Then, upon refluxing, carbonyl species in the same oxidation state are obtained, presumably as a result of HCl-mediated DMF decomposition. Provided that water levels are kept low, reduction can occur to provide the complexes [NH2(CH3)2][RhCl2(CO)2], [NH2(CH3)2][RuCl3(CO)2(DMF)], [RuCl2(CO)2(DMF)2], and [NH2(CH3)2][IrCl2(CO)2]. In the case of platinum, reduction is not effective and [NH2(CH3)2][PtCl3(CO)] is obtained. No carbonylpalladium species can be synthesized in this way, the reaction producing copious amounts of colloidal metal. Adding phosphanes to these chlorocarbonyl-containing solutions allows easy, one-step syntheses of a variety of complexes.

MOCVD of rhodium, palladium and platinum complexes on fluidized divided substrates: Novel process for one-step preparation of noble-metal catalysts

A new one-step method, entitled fluidized-bed metal-organic chemical vapor deposition (FBMOCVD) of preparing highly dispersed metal-supported catalysts is reported. The following complexes were studied and used as CVD precursors in presence of H2: [Rh(m-Cl)(CO)2]2, Rh(allyl)3, Rh(acac)(CO)2, Pd(allyl)(hfac), Pd(allyl)(Cp), Pt(COD)(CH3)2. (acac, acetylacetonato; hfac, hexafluoroacetylacetonato; Cp, cyclopentadienyl; COD, cyclooctadienyl). In a first approach, depositions on planar substrates were carried out to establish the best experimental conditions to obtain good-quality deposits. X-ray diffraction, X-ray photo-electron spectroscopy and electron microprobe studies were realized on the resulting thin films. Analyses of the products contained in the gas phase after and during deposition were performed by mass spectrometry and GC‐MS. Finally, catalysts prepared by FBMOCVD were characterized by transmission electron microscopy‐energy dispersion spectroscopy (TEM‐ EDS), metal-loading determinations and specific-surface measurements (BET). Dispersed nanosized aggregates were obtained, showing high activities in alkene hydrogenation and alcohol hydrocarbonylation. # 1998 John Wiley & Sons, Ltd.

Fluidization, Spouting, and Metal–Organic CVD of Platinum Group Metals on Powders

In the first part of this paper, processes used for the fluidization of particles in a CVD reactor are reviewed, then the concept of the spouted bed is introduced, and the possibility of using it in association with metal-organic (MO)CVD is discussed. In the second part, the particulars of the MOCVD of platinum group metals are recalled. Finally, the MOCVD of these metals in fluidized bed and spouted bed reactors is illustrated with results obtained during two research projects, one of which concerns the preparation of finely dispersed rhodium, platinum, and palladium-based catalysts by fluidized bed MOCVD, the other, the doping of NiCrAlY powders (a raw material for thermal barriers) with ruthenium by spouted bed MOCVD. Results on the morphology and purity of the deposits are presented, and the applicability of such techniques, either for industrial uses or for initial screening of dopants (nature and level), are discussed.

Rhodium and palladium complexes from 1,1′ and 1,2 ferrocenylphosphine as bidentate ligands. Versatile coordination

Abstract The complexation of the mixed bidentate ligands 1-diphenylphosphino-1′-diphenylthiophosphinoferrocenyl and 1,2-bis(diphenylphosphino)ferrocenyl with rhodium(I) and palladium(II) species yield a range of mono- and dirhodium or palladium complexes. Their interest as possible catalysts for alkene hydroformylation and alkoxycarbonylation and Heck coupling reactions has been assessed. Fe[C5Me4P(S)Ph2][C5Me4PPh2]PdCl2 and Fe[C5H2-1,2-(PPh2)2-4-tBu][C5H5]PdCl2 have been characterized by single-crystal X-ray diffraction studies.

A new OMCVD iridium precursor for thin film deposition

Deposits of noble metals, particularly Pt, Pd, Rh, or Ir, prepared by CVD are of particular interest because of their low resistivity and high thermal stability. The major application is in microelectronics where they can replace gold as interconnectors and contacts; other potential applications are protective coatings, gas sensors, or catalysts. Our interest in the latter field has prompted us to develop a CVDfluidized bed reactor in order to prepare supported catalysts that are highly dispersed on porous substrates. Among the noble metals cited above, iridium has been the subject of only a few studies, and suitable CVD precursors (i.e., volatile, easily synthesized, thermally stable during gas phase transport, characterized by a clean decomposition, and non-toxic) are relatively scarce. Iridium halides yield high quality films on graphite substrates at temperatures near 800 C under an H2/CO/Ar atmosphere. [3] Iridium acetylacetonates provide deposits with measurable impurity levels above 500 C, but addition of a small amount of oxygen gas allows the production of high-purity films in the same temperature range. Tris-(allyl)-iridium(III), an airsensitive precursor, was used to produce clean deposits at temperatures as low as 100 C, under H2, on SiO2 substrates. (1,5-COD)(Cp)Ir and (1,5-COD)(CpMe)Ir were used by Hoke et al. to produce high purity films in the range 120±160 C. Finally, very recently (1,5-COD) (hfac)Ir and (1,5-COD)(thd)Ir (where hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate and thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) were used to deposit thin films at 250 C to 400 C on SiO2/Si, Pt/Si, and Cu/Si substrates. [7] The easy and highyield synthesis of a new iridium volatile precursor was desirable. Surprisingly, although carbonyl complexes are often used in OMCVD, they have not yet been used for deposition of iridium. In this work, we report a new and simple synthesis of [Ir(l-SC(CH3)3)(CO)2]2 (tetracarbonyl bis(l-(2methyl-2-propane-thiolato))diiridium), and the preliminary studies of its use as precursor for OMCVD on planar graphitic carbon substrates. The previously reported synthesis of [Ir(l-SC(CH3)3)(CO)2]2 requires three steps and produces a clean complex with a 60 % yield based on iridium salt; no particular information concerning its volatility is available. We describe here a facile one-step synthesis that consists of the production of the [IrX2(CO)2] ± (X = Cl, I) anion from iridium salts and of its reaction with 2-methyl-2-propanethiol. This complex (Fig. 1), stable to air and moisture, has been characterized by H and C NMR, FTIR, and mass spectrometry

Rhodium-catalyzed hydrocarbonylation of acetic acid into higher acids

Abstract The hydrocarbonylation of acetic acid into higher homologues catalyzed by rhodium/iodide systems has been investigated at 20 MPa and 220°C. In homogeneous catalysis the most convenient precursor proved to be [RhI 2 (CO) 2 ] − prepared from [RhCl(CO) 2 ] 2 in the presence of LiI; mean turnover frequencies of 67 h −1 and selectivities as high as 80% in propionic acid were obtained. In addition, in heterogeneous catalysis, rhodium supported upon activated carbon was observed to be an efficient system for the conversion of acetic acid into propionic acid (80% selectivity) in a fixed bed reactor. The reaction mechanism is thought to be an iodoacetyl rather than an ethanol pathway in the homogeneous system, while the two seem likely to be in operation in the heterogeneous system.

Dimethylformamide as a convenient CO source for the facile preparation of rhodium-, iridium- or ruthenium-chlorocarbonyl complexes directly from RhCl3·3H2O, IrCl3·3H2O or RuCl3·3H2O

Abstract The anionic complexes [RhCl 2 (CO) 2 ] − , [IrCl 2 (CO) 2 ] − or [RuCl 3 (CO) 2 (DMF)] − can be obtained in high yields (up to 85 %) and in less than 60 min by refluxing dimethylformamide solutions of RhCl 3 ·3H 2 O, IrCl 3 ·3H 2 O or RuCl 3 ·3H 2 O. Depending on the metal, the presence of small amounts of water and/or hydro- chloric acid greatly accelerates the reduction step. For rhodium, several intermediates have been trapped which allow us to propose a mechanism for this reaction.