THE EFFECTS OF BORON ADDITION AND PRESULFIDATION TEMPERATURE ON THE HDS ACTIVITY OF A Co-MoS2/Al2O3 CATALYST

Abstract

The effect of boron addition was studied on the hydrodesulfurization (HDS) of thiophene over Co-MoS₂/B/Al₂O₃ (CVD-Co/MoS₂/B/Al₂O₃), which was prepared by a CVD technique using Co(CO)₃NO as a precursor of Co. The catalyst was characterized by means of NO adsorption, XPS, Raman Spectroscopy, FTIR, and TEM. The HDS activity of CVD-Co/MoS₂/B/Al₂O₃ catalyst increased as the boron content increased up to about 0.6 and 1.2 wt% B for the catalyst presulfided at 673 and 773 K respectively, followed by a decrease with a further addition of boron loading. In spite of the activity increase, the amount of NO adsorption on MoS₂/B/Al₂O₃ steadily decreased with increasing boron loading, suggesting that the dispersion of MoS₂ particles is decreased by the addition of boron. Selective formation of the CoMoS phase on CVD-Co/MoS₂/B/Al₂O₃ was achieved by the CVD technique. The TOF of the HDS over the CVD-Co/MoS₂/B/Al₂O₃ catalyst, defined by the activity per Co atom forming the CoMoS phase, increased as high as 1.6 and 1.9 times for the catalyst presulfided at 673 and 773 K, respectively. It is concluded that the addition of boron weakens the interaction between Mo oxides and Al₂O₃ surface, promoting the formation of the so called Co-Mo-S ";;;pseudo";;; type II over CVD-Co/MoS₂/B/Al₂O₃ presulfided at 673 K. The Co-Mo-S ";;;pseudo";;; type II is a metastable phase with the TOF value intermediate between Co-Mo-S type I and type II. With CVD-Co/MoS₂/B/Al₂O₃ presulfided at 773 K, the addition of boron promotes the formation of ";;;real";;; Co-Mo-S type II, possibly by the formation of well-crystallized MoS₂ structure.