In the oxidation of gluconic acid with platinum on carbon as catalyst, a deactivation of the catalyst takes place due to both chemisorption of oxygen (formation of PtO) and oxidation of the platinum surface (formation of PtO2). Both types of deactivation can be reversed by temporarily replacing the oxygen flow by a nitrogen flow. Chemisorbed oxygen reacts relatively rapidly with the intermediate product guluronic acid and relatively slowly with gluconic acid and glucaric acid. Consequently, the degree of coverage by chemisorbed oxygen changes in batch experiments due to the change of the concentration of gluconic acid and its reaction products. The deactivation due to the formation of PtO2 and the oxidation reaction are chemically coupled, and are explained in the same way as in the oxidation of glucose.