Solution synthesis of the unsupported Ni–W sulfide hydrotreating catalysts
Résumé
Three solution synthesis routes for the preparation of unsupported Ni–W–S hydrotreating catalysts were compared. In all of them WO2S2 2- core was applied as precursor, but the reaction between Ni and W species was done in different ways. The preparation methods included solution reaction between WO2S2 2- and nickel species in the presence of organic surfactant (liquid–liquid route), reaction of amorphous high surface area nickel compound with aqueous WO2S2 2- species (liquid–solid route) and reaction of amorphous WOS2 solid with aqueous solution of nickel salt (solid–liquid route). The catalysts were characterized by several techniques including X-ray powder diffraction, specific surface area and pore volume measurements, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The catalytic activities were evaluated in thiophene hydrodesulfurization (HDS), toluene hydrogenation (HYD) and pyridine hydrodenitrogenation (HDN) reactions. It has been shown that highly active unsupported sulfides can be obtained from three routes. The highest weight activity was observed for the most finely dispersed liquid– liquid preparation. However, the relation between catalytic activity and texture is not linear and the preparation having low surface area and containing NiS bulky particles covered by curved WS2 slabs showed the highest activity per unit of surface area.