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

The effect of boron addition was studied on the hydrodesulfurization ( HDS) of thiophene over Co - MoS 2 / B/ Al 2 O 3 (CVD-Co/MoS 2 /B/Al 2 O 3 ), which was prepared by a CVD technique using Co(CO) 3 NO 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 / MoS 2 / B/ Al 2 O 3 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 MoS 2 /B/Al 2 O 3 steadily decrease d with increasing boron loading, suggesting that the dispersion of MoS 2 particles is decreased by the addition of boron. Selective formation of the CoMoS phase on CVD-Co/MoS 2 /B/Al 2 O 3 was achieved by the CVD technique. T he TOF of the HDS over the CVD-Co/MoS 2 /B/Al 2 O 3 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 Al 2 O 3 surface, promoting the formation of the so called Co-Mo-S ";;;pseudo";;; type II over CVD-Co/MoS 2 /B/Al 2 O 3 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/MoS 2 /B/Al 2 O 3 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 MoS 2 structure. Keywords: Hydrodesulfurization; Co-Mo sulfide catalysts; Effect of boron addition; CVD technique; Turnover frequency