Reactive carbon dioxide desorption was studied on stepped Pt(112) by means of angle-resolved thermal desorption combined with a cross correlation time-of-flight technique. Heating of the co-adlayer of CO(a) and O(a) yields three CO 2 formation peaks, i.e., P 1 -CO 2 (at 400 K), P 2 -CO 2 (300 K), and P 3 -CO 2 (230 K). Their angular distributions are sharply collimated closely to the terrace normal. The reaction occurs almost on the terrace. At small CO coverages, only P 1 -CO 2 is formed. Its angular distribution is asymmetric, indicating desorption from steps. The velocity distribution measurements of desorbing CO 2 confirm the presence of the above desorption components.