<p>The desulfurization performance for Mn-Ni supported on activated carbons (Mn-Ni/NAC) calcined at different temperatures varies considerably. The physicochemical properties of Mn-Ni/NAC have been investigated by a series of characterization studies. The moderate calcination temperature contributed to a larger surface area and abundant oxygen-containing functional groups (C = O), thus provided more anchoring sites for the dispersion of Mn²⁺ and Ni⁰ species. The optimal Mn-Ni/NAC-700 exhibited superior desulfurization performance, achieving breakthrough sulfur capacity and breakthrough time of 287&#xa0;mg/g and 531&#xa0;min, respectively. The nucleophilic C = O groups served as active sites for chemically absorbing SO₂. Ni⁰ could serve as an oxygen activator, and promote the transfer of oxygen molecules to oxidize SO₂. During the desulfurization, SO₂ adsorbed on the C = O groups gradually mainly converted into sulfate (SO₄²⁻). This conversion process was closely linked to the decrease of surface C = O groups and the formation of C–O groups. As the reaction proceeds, reaction products (SO₄²⁺) begin to accumulate, blocking the pore channels of the catalyst and generating MnSO₄, resulting in catalyst deactivation. This work will guide the design of high-performance activated carbon-based adsorbents suitable for practical applications.</p>