Comparative study of activity and selectivity of transition metal sulfides in parallel hydrodechlorination of dichlorobenzene and hydrodesulfurization of methylthiophene

Carbon-supported sulfides of V, Cr, Mn, Fe, Co, Ni, Mo, Ru, Rh, Pd, W, Ir, and Pt were compared in parallel hydrodechlorination (HDC) of o-dichlorobenzene and hydrodesulfurization (I-IDS) of 3-methylthiophene at 300 degrees C and 1 MPa in a flow reactor. The reference catalyst was a commercial hydrotreating Ni-Mo/Al2O3 sulfide catalyst. The work was related to disposal of chlorinated organic wastes contaminated by sulfur and to HDC in organic technology. The kinetics were described by means of a parallel consecutive scheme of pseudo first-order reactions. Pt-group metal sulfides exhibited the highest HDS activity but their ranking did not fully correlate with literature results on HDS in the absence of HDC, the maximum activity being at Pd and Pt in the second and third rows, respectively. The Pd sulfide was by far the best HDC catalyst showing about two times higher activity than the reference Ni-Mo sample. The ranking of the sulfides in HDC corresponded with published reports on comparative studies on HDC over metals. The selectivity to intermediate chlorobenzene was the highest on Pd and the lowest on Ni-Mo, with maximum conversions to chlorobenzene during the reaction of 64 and 15%, respectively. HDC was faster than HDS over the conventional Ni-Mo system but the behavior of other sulfides was very heterogeneous. The Ni sample was very selective to HDC (HDC conversion of 90% at HDS conversion of 10%), the Pt and Ir sulfides were very selective to HDS (HDC conversion of 10% at HDS conversion of 90%), and the rates of HDC and HDS were about the same over the Mo sulfide. The features of the parallel HDC/HDS were discussed in the relation to performance of metal sulfides in other hydrotreating reactions: HDS in the absence of chlorine compounds, hydrodearomatization, and hydrodenitrogenation. (C) 1997 Academic Press.