Flame spray synthesis of CoMo/Al2O3 hydrotreating catalysts Original Research Article

The first alumina supported and unsupported cobalt molybdenum hydrotreating catalysts have been prepared by one-step flame spray pyrolysis (FSP) by spraying and combusting tris(acetylacetonato)aluminum, cobalt 2-ethylhexanoate and molybdenum 2-ethylhexaoate dissolved in toluene. The oxide particles produced contained varying amounts of transition metals (8, 16, 24 and 32 wt.% Mo with atomic ratio Co/Mo = 1/3 and 16 wt.% Mo with atomic ratios Co/Mo = 2/3 and 1/1) with alumina constituting the balance. In addition, an unsupported reference catalyst (atomic ratio Co/Mo = 1/3) was produced. The particles obtained consisted mostly of γ-Al2O3 with some CoAl2O4, as evidenced by X-ray diffraction (XRD) and UV–vis spectroscopy. Bulk MoO3 was not detected by XRD, except at the highest molybdenum content (32 wt.%) and in the unsupported sample, indicating that molybdenum is well dispersed on the surface of the support. The specific surface area as measured by nitrogen adsorption (BET) decreased from 221 to 90 m2/g when going from the lowest loading supported catalyst (8 wt.%) to the unsupported reference. Transmission electron microscopy (TEM) images showed that at low molybdenum loadings nanoparticle agglomerates with 5–10 nm primary particles were produced. As the molybdenum loading on the alumina was increased from 8 to 32 wt.% and for the unsupported reference the primary particle size increased to up to 20 nm and the morphology became more irregular due to primary particle sintering and aggregation.