Roselyne Feurer

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.

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.

Platinum, palladium and rhodium complexes as volatile precursors for depositing materials

Abstract This article reviews the transition-metal complexes of rhodium, palladium and platinum which were described in the literature as volatile. A classification has been adopted according to the ligands borne by each metal center, and the preparation procedures have been given. As the general aim of the review is to use the most convenient complexes for chemical vapor deposition, the yields of the syntheses and the stability and/or sensitivity of the complexes have been emphasized. When appropriate, their use in CVD and a detailed description of the resulting deposits have been reported. Challenges for researchers in the field are discussed.

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.

Metal-organic chemical vapor deposition in a fluidized bed as a versatile method to prepare layered bimetallic nanoparticles

Abstract Bimetallic supported layered nanoparticles, with an inner nucleus of platinum and an outer shell of palladium were synthesized by two successive chemical vapor deposition runs in a fluidized bed from Pt(Me)2(COD) at 120°C and Pd(η3-C3H5)(hfacac) at 60°C, these remarkable mild conditions allowing in the presence of H2 to reach pure metal particles sized between 5 and 15 nm. Both TEM and EDX analyses evidenced the layered structure. The preliminary studies on catalytic dehydrogenation showed the great activity and stability of these bimetallic materials.

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

Thermal decomposition of V(NEt2)4 in an MOCVD reactor: a low-temperature route to vanadium carbonitride coatings

Carbon-rich vanadium carbonitride films have been grown by MOCVD at low temperature using the tetrakis(diethylamido) vanadium complex V(NEt2)4 as a single-source precursor. The main volatile byproducts formed during its thermal decomposition were identified by NMR and on-line mass spectrometric analyses. Under the growth conditions, an equimolecular ratio of HNEt2 and EtNCHMe was found in addition to CH3CN and C2H4. From these results, an elimination mechanism of the NEt2 ligands is proposed. It accounts for their high lability and therefore the low nitrogen content of the films. The possible origin of the incorporation of the metalloid elements is also discussed.

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.

Mécanisme de décomposition des composés M(NEt2)4 (M = V, Cr) lors de leur utilisation comme mono-source pour la croissance de films M-C-N par MOCVD

Abstract Both NMR identification of the decomposition by-products of the organometallic compounds M(NEt 2 ) 4 (M = V, Cr) and on line mass spectrometry analyses in the MOCVD reactor have been used, in relation with the main features of the films, to discuss a decomposition pathway which accounts for the lability of the NEt 2 ligands and accordingly the low nitrogen content of the films.

Characterisation and reactivity of activated carbon supported platinum catalysts prepared by fluidised bed organometallic chemical vapour deposition (FBOMCVD)

Publisher Summary In the course of developing new methods for the preparation of heterogeneous catalysts, this chapter illustrates that the combination of organometallic chemical vapor deposition (OMCVD) and the fluidization of a bed of porous particles is a powerful method to prepare supported catalysts. Highly dispersed deposits of rhodium, palladium, and platinum on metal oxide supports were obtained in a single step using a fluidized bed reactor. The method of chemical vapor deposition (CVD) allows direct deposition of the active phase onto the catalyst support by means of the reaction between surface sites containing oxygenated groups and the vapor of a suitable organometallic compound. Using silica or alumina with large specific areas—around 200 m 2 g -1 —the presence of hydroxyl groups on the surface allows the facile grafting of small and dispersed particles of the noble metal (2–5 nm).