Influences of nitrogen species on the hydrodesulfurization reactivity of a gas oil over sulfide spent catalysts

Spent NiMo and CoMo alumina catalysts were evaluated in the HDS reactivities of gas oil and its nitrogen species-free oil, in term of gross and molecular based desulfurization behaviors. Spent catalysts lost their activity apparently due to the carbon deposition, which covered the active sites. Such carbon deposition reduced the acidity of NiMo catalyst while activity of CoMe could survive. Such carbon deposition changed the catalyst performances for the HDS against reactive and refractory sulfur species of original and NF oil in single and two-stage reaction. The activity for refractory sulfur species was reduced more than that for the reactive species. The effect of two-stage and n-removal were markedly reduced over spent NiMo while rather limited over spent CoMo. Loss of activity by carbon deposition might be related with such changes in catalytic selectivity.