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.