Preparation and Characterization of Mo/W Bimetallic Carbides by Using Different Synthesis Methods
- PDF / 393,694 Bytes
- 8 Pages / 595.276 x 790.866 pts Page_size
- 86 Downloads / 194 Views
Preparation and Characterization of Mo/W Bimetallic Carbides by Using Different Synthesis Methods Luiz C. A. Bastos Æ Waldinei R. Monteiro Æ Marisa A. Zacharias Æ Gilberto M. da Cruz Æ Jose´ Augusto J. Rodrigues
Received: 17 June 2007 / Accepted: 21 August 2007 / Published online: 11 September 2007 Springer Science+Business Media, LLC 2007
Abstract Molybdenum and tungsten bimetallic oxides were synthetized according to the following methods: Pechini, coprecipitation and solid state reaction (SSR). After the characterization, those solids were carbureted at programmed temperature. The carburation process was monitored by checking the consumption of carburant hydrocarbon and CO produced. The monitoring process permits to avoid or to diminish the formation of pirolytic carbon. Keywords Molybdenum Tungsten Bimetallic Oxide Carbide
1 Introduction In 1971, Sinfelt and Yates [1] demonstrated that the molybdenum carburation provided a big increase in the specific activity of this metal with the ethane hydrogenolisis. Several subsequent studies state that carbides and metallic transition nitrides are active catalysts in several chemical reactions in which noble metals are normally used [2, 3].
L. C. A. Bastos (&) G. M. da Cruz Chemical Engineering Department, Engineering School of Lorena, University of Sa˜o Paulo, Estrada Municipal do Campinho, s/n, P.O. Box 116, Lorena, SP 12602-810, Brazil e-mail: [email protected] W. R. Monteiro M. A. Zacharias J. A. J. Rodrigues Combustion and Propulsion Associate Laboratory, National Institute of Spatial Development (INPE), Rodovia Presidente Dutra, Km 40, Cachoeira Paulista, SP 12630-000, Brazil J. A. J. Rodrigues e-mail: [email protected]
123
A good performance of these new materials in traditional reactions catalyzed by noble metals is attributed to an increasing electronic density of the metal after carburation and/or nitriding. The introduction of carbon or nitrogen at the unit cell of those metals results in an increase of net parameter a. Considering the fact that the electronic band is proportional to 1/a5, the increase of the metal–metal distance causes a contraction in band d and generates electronic densities similar to those found in noble metals [4, 5]. Among the most important reactions in which these materials can be used, there are reactions of hydrotreatment of petroleum fractions, the most important of them are the catalytic hydrogenation with sulphur removal (HDS) and the one with nitrogen remotion (HDN) [6]. From the year 80 onward, the investigations involving carbides and nitrides got a big recognition with the discovery made by Volpe and Boudart who demonstrated that it was possible to obtain tungsten nitrides or molybdenum nitrides with higher specific areas by the nitriding at programmed temperature of the respective oxides with ammonia [7]. Since then, the synthesis method of nitrides and carbides at programmed temperature, were started to be investigated well. Lee et al. [8] syntethized molybdenum carbides with higher specific areas
Data Loading...
