Abstract Al2O3 has been considered as an effective sorbent of lead removal from the SO2-containing flue gas. The reaction chemistry between PbCl2 and SO2 over Al2O3 surface was systemically explored by quantum chemistry calculations. The results suggest that the chemisorption mechanism is responsible for PbCl2 and SO2 adsorption over Al2O3 surface. The intense orbital hybridization and overlap are related to strong chemisorption of PbCl2 and SO2 over Al2O3 surface. PbSO4 can be produced from the reaction between PbCl2 and SO3 generated from SO2/SO3 transformation. SO2/SO3 transformation includes three steps: SO2 → SO2(ads) → SO3(ads) → SO3. The reaction pathway between PbCl2 and SO3 over Al2O3 surface contains six steps: O2 adsorption, SO3(ads) → SO4(ads), PbCl2 → PbCl2(ads), PbCl2(ads) → PbSO4(ads), PbSO4 desorption, and Cl2 desorption. The rate-determining step (RDS) of PbSO4 formation over Al2O3 surface is SO2 oxidation due to its larger energy barrier. The activation energy barriers of SO2 oxidation over Al2O3 (0 0 1) and Al2O3 (1 1 0) surfaces are 114.56 and 416.03 kJ/mol, respectively. Al2O3 (0 0 1) surface exhibits higher activity for PbSO4 formation than Al2O3 (1 1 0) surface. This study of reaction mechanism can be conducive to better comprehend the transformation of lead species on Al2O3 sorbent in the presence of SO2.