Spinel nano-Co 3 O 4 was prepared by solid-state reaction at room temperature and investigated for selective catalytic reduction of NO x by NH 3 (NH 3 -SCR). Although suffering from pore filling and plugging, treatment of this catalyst by SO 2 showed novel promoting effect on NH 3 -SCR above 250°C. Bulk cobalt sulfate was observed over the sulfated Co 3 O 4 with XRD, which would be an active component for NH 3 -SCR. The sulphated Co 3 O 4 catalyst exhibited good resistance to SO 2 (500ppm, 100ppm) and 10% H 2 O at a space velocity of about 25000h −1 at 300°C, as tested for 12h.