Display omitted •Sulphided CoMo/γ-Al2O3 catalysts were prepared based on orthogonal design.•Near 100% efficiency was achieved for the removal of SO2 from flue gas.•SO2 is completely converted into elemental S by the Al-S400-0.31 catalyst.•Mechanism for selective catalytic reduction of SO2 to elemental S was proposed. This study aimed to develop sulphided CoMo/γ-Al2O3 catalysts to recover elemental sulphur via selective reduction and to understand the catalytic mechanism of the selective catalytic reduction (SCR) of SO2 into sulphur when CO is used as the reducing agent. A series of catalysts were prepared based on Taguchi’s L9 orthogonal array and were evaluated in terms of their SO2 conversion efficiency, selectivity of SO2 reduction to elemental sulphur, elemental sulphur yield, and selectivity of COS formation. It is found that the catalyst sulphided at 400°C with a ratio of Co/(Co+Mo)=0.31 and supported on γ-Al2O3 had the best performance among all the catalysts studied. In addition, the physical–chemical properties and catalytic activities of this catalyst were studied systematically. The mechanism of selective reduction of SO2 to elemental sulphur using CO as the reducing agent was therefore proposed.