In the preparation of O₂ from KClO₃, MnO₂ acts as

O₂ is prepared in the laboratory by thermal decomposition of potassium chlorate in the presence of manganese dioxide as catalyst

$2{\mathrm{KClO}}_3 \stackrel{{\mathrm{MnO}}_2 , 425\mathrm{K}}{\to } 2\mathrm{KCl} + 3{\mathrm{O}}_2$