ESR studies on hydrodesulfurization catalysts : nickel- or cobalt-promoted sulfided tungsten- or molybdenum-containing catalysts

ESR spectra of nickel- or cobalt-promoted sulfided tungsten- or molybdenum-containing catalysts are measured together with the influence of equilibration at different H2S/H2 ratios and CO adsorption hereon. The ESR measurements are compared with thiophene hydrodesulfurization (HDS) activities. The influence of nickel and cobalt on the ESR spectra is essentially the same. This similarity also holds for the thiophene HDS activities. A new signal VI (g = 2.06, ¿H = 220 G for Ni---Mo; g = 2.08, ¿H = 220 G for Ni---W) not occurring in unpromoted catalysts is detected. The intensities of signals II, III, IV, and VI are dependent on the composition of the interacting atmosphere. The results are discussed in terms of WS2(MoS2) crystallite edge decoration with promotor ions. Possible surface configurations corresponding with the different paramagnetic sites are described