CCl4-Assisted Preparation of Highly Dispersed Molybdenum and Tungsten Nitrides

P. Afanasiev (1) , D. Laurenti (1)

1 RAFFINAGE - RAFFINAGE

Nanoscopic transition metal nitrides were prepared by means of a newly developed technique, using nanoparticles of scheelites (AMO(4), A = Ca, Sr, Ba; M = Mo, W) as precursors. After treatment with CCl4-NH3 gas mixtures the precursor salts were transformed to mixtures of alkali earth chlorides (ACl(2)) and transition metal nitrides (M2N). The thermodynamic driving force of the process is the high free enthalpy of the simultaneous formation of carbon dioxide and an electropositive chloride, from the interaction between CCl4 and AMO(4). As a result, the gas-solid reaction occurs at relatively low temperature (500-550 A degrees C). After water extraction of soluble chlorides, finely dispersed solids Mo2N (x) C (y) and W2N (x) C (y) (x = 0.79-0.95, y = 0.03-0.15) were obtained, which demonstrated high specific surface areas and well developed mesoporosity. Their catalytic activity was compared in the thiophene hydrodesulfurization reaction, where the active phase is provided by MS2 sulfides formed in situ under the reaction conditions, as confirmed by temperature-programmed reduction. Due to their open porosity, the solids as obtained demonstrated high activity and increased stability as compared to the same nitrides prepared by means of other techniques. The catalytic activity of the newly prepared nitrides was evaluated in the guaiacol hydrodeoxygenation (HDO) reaction. Molybdenum nitride showed promising HDO performance and unusual selectivity, whereas the tungsten homolog demonstrated poor activity.

Domaines: Catalyse; Environnement et Société

P. Afanasiev, D. Laurenti. CCl4-Assisted Preparation of Highly Dispersed Molybdenum and Tungsten Nitrides. Topics in Catalysis, 2012, 55, pp.940-949. ⟨10.1007/s11244-012-9878-z⟩. ⟨hal-00752591⟩