[en] The CO oxidation reaction on Rh field-emitter surfaces has been investigated for both high-pressure and low-pressure conditions. In the high-pressure studies the Rh surface was heated to 500 K in 1-2 Torr of O₂/CO mixtures and was subsequently analyzed by imaging atom-probe mass spectroscopy. The detection of surface oxides only at O₂/CO ratios in excess of 30/1 identifies oxide formation as the surface process responsible for deactivation of the reaction. In the low-pressure experiments the Rh surface was analyzed by pulsed-laser atom-probe mass spectroscopy while the CO oxidation reaction was taking place. The electric field and temperature dependence of the detected ion intensities indicated that the electric field does not strongly influence the CO oxidation reaction or the thermal desorption of CO. No indication of crystallographic specificity in the adsorption of oxygen or CO was observed