Synthesis and Characterization of Molybdenum Based Colloidal Particles Beatriz Moreno,* ,1 Olivia Vidoni,* Cesar Ovalles,* Bruno Chaudret,† Caribay Urbina,‡ and Heinz Krentzein‡ *INTEVEP, S.A., Apdo. 76343, Caracas 1070A, Venezuela; †Laboratoire de Chimie de Coordination du CNRS, Route de Narbonne, 31077 Toulouse, Cedex, France; and ‡Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela Received January 21, 1998; accepted May 1, 1998 The synthesis and characterization of molybdenum colloidal particles were evaluated using thermal and sonochemical methods and starting from different metal precursors, Mo(CO) 6 and (NH 4 ) 2 MoS 4 . The prod- ucts were characterized by elemental analysis, spectroscopic (UV, FTIR), and surface analysis (XPS) techniques, as well as by trans- mission electron microscopy (TEM) for determining the particle sizes. Using Mo(CO) 6 as metal source, particle sizes with an average diam- eterof 1.5 nm can be obtained using tert-amyl alcohol as solvent and tetrahydrothiophene as sulfurating ligand. The characterization of these particles showed that they are composed of molybdenum oxide MoO 3 . Using (NH 4 ) 2 MoS 4 as metal precursor, particles with average diameters of 4.7 and 2.5 nm were synthesized using thermal and sonochemical methods, respectively. The characterization of these particles showed them to be composed of molybdenum sulfide, MoS 2 . The sonochemical method proved to be the fastest and most conve- nient synthetic pathway of obtaining small colloidal particles at low temperatures and with control of the average size. © 1998 Academic Press Key Words: colloidal particles; molybdenum; synthesis. INTRODUCTION The interest for the preparation and characterization of highly dispersed metal particles has grown considerably in the last few years mainly because of their potential use in catalysis (1, 2) and in material science (3, 4). In general, no discontinuity has been observed between metal particles containing very few atoms (clusters) and large particles of size up to several hun- dreds of nanometers (metal colloids and crystallites) (1, 2, 5). Furthermore, colloidal metal particles or large metal clusters have been described (5) as bridges between homogeneous and heterogeneous catalysts and, in most cases, have diameters larger than 10 nm. These metal particles exhibit unique cata- lytic properties, and their study is of academic and industrial importance (1–5). In particular, the use of highly dispersed molybdenum sul- fide catalysts is of great interest because of their known prop- erties for catalyzing coal liquefaction (6, 7), heavy crude oil upgrading (8 –11), and alcohol synthesis from syngas (12, 13). Different methods have been used for the preparation of these catalysts. The most common procedure consists of thermal decomposition of organosoluble molybdenum compounds such as naphthenate (9, 10) or acetylacetonate (8, 11). How- ever, the control of particle size as well as the complete characterization of the metal colloids and crystallites is not yet fully accomplished (1, 2, 5). Osseo-Asare et al. reported the synthesis of molybdenum sulfide particles in the 10 – 80 nm range using a nonylphenol– ethylene oxide/cyclohexane/water microemulsion system and (NH 4 ) 2 MoS 4 as a source of metal (14). The particles were synthesized by acidifying ammonium tetrathiomolybdate sol- ubilized in the water cores of inverse micelles. These authors reported that the small size and the cage-like nature of the emulsion droplets controls particle growth and aggregation. The particle size was found to depend on the water-to-surfac- tant molar ratio and the average number of ammonium tetra- thiomolibdate ions (MoS 4 2- ) solubilized per water droplet (14). Besides the work by Osseo-Asare et al. (14) there are no comprehensive reports in the literature to address the question of what is the best experimental procedure for preparing mo- lybdenum sulfide colloidal particles. Therefore, the objective of this work is to evaluate thermal and sonochemical methods for synthesizing these colloidal particles starting from different metal precursors (Mo(CO) 6 and (NH 4 ) 2 MoS 4 ). The products were characterized by elemental analysis, spectroscopic (UV, FTIR), and surface analysis (XPS) techniques as well as by transmission electron microscopy to determine the particle sizes. EXPERIMENTAL SECTION General Methods All operations were carried out using standard Shlenck tube techniques or Fisher–Porter bottle techniques under inert at- mosphere (Ar, N 2 ). Solvents were purified just before use by distillation under nitrogen atmosphere: methanol was purified by distillation over iodine–magnesium, tert-amyl alcohol was distilled from CaH 2 , and anhydrous diethyl ether was used as received. All solvents were deoxygenated prior to use. H 2 /CO 1 To whom correspondence should be addressed. E-mail: rppcbm1-int@ intevep.pdv.com. JOURNAL OF COLLOID AND INTERFACE SCIENCE 207, 251–257 (1998) ARTICLE NO. CS985631 251 0021-9797/98 $25.00 Copyright © 1998 by Academic Press All rights of reproduction in any form reserved.