The hydrogenation activity of a heteroatom removal catalyst, having
activity for both heteroatom removal and hydrogenation, is selectively
suppressed by a treatment which comprises contacting the catalyst with
(i) hydrogen, (ii) a selectively deactivating agent that suppresses the
catalyst's hydrogenation activity, and (iii) a protective agent, such as
CO, that preserves and protects the heteroatom removal activity during
the treatment. This may be achieved in a reactor while it is on-line and
removing heteroatoms from a hydrocarbon feed.