Calorimetric measurement of catalytic surface reaction heat: CO oxidation on Pt{110}

Abstract

The technique of single crystal adsorption microcalorimetry has for the first time been applied to the study of a catalytic reaction, namely the oxidation of CO on a Pt{110} substrate at room temperature. By comparing the measured heat deposited in the crystal with that expected for the reaction, the excess energy removed by the desorbing CO2 molecules can be deduced. It is found that when CO is dosed onto a saturated oxygen overlayer, the product CO2 molecules remove only 9±17 kJ mol−1 more energy than expected for thermally accommodated molecules. However, when oxygen is dosed onto a CO overlayer, the product CO2 molecules remove 52±21 kJ mol−1 of excess energy. We suggest that the more highly excited CO2 molecules are formed by reaction of CO molecules with ‘‘hot’’ oxygen adatoms produced by the dissociation process and not thermally accommodated to the surface.