We report our investigation of the interaction of NO2 with the Au(997)vicinal surface by high-resolution photoelectron spectroscopy using synchrotron radiation as the excitation source.At 170 K,both core-level and valence-band photoemission results illustrate the decomposition of NO2 on the Au(997)surface at low NO2 exposures,forming coadsorbed NO(a)and O(a)species.After annealing at 300 K,NO(a)desorbs from Au(997)whereas O(a)remains on the surface.Upon annealing at 750 K,we observe no signal for adsorbed oxygen on Au(997).These results clearly demonstrate that thermal decomposition of NO2 is an effective method to generate oxygen adatoms on Au(997)under ultrahigh-vacuum conditions.
Adsorption and reaction of CO and CO_2 were studied on oxygen-covered Au(997) surfaces by means of temperature- programmed desorption/reaction spectroscopy. Oxygen atoms(O(a)) on Au(997) enhances the CO_2 adsorption and stabilizes the adsorbed CO_2(a), and the stabilization effect also depends on the CO_2(a) coverage and involved Au sites. CO_2(a) desorption is the rate-limiting step for the CO+O(a) reaction to produce CO_2 on Au(997) at 105 K and exhibits complex behaviors, including the desorption of CO_2(a) upon CO exposures at 105 K and the desorption of O(a)-stabilized CO_2(a) at elevated temperatures. The desorption of CO_2(a) from the surface upon CO exposures at 105 K to produce gaseous CO_2 depends on the surface reaction extent and involves the reaction heat-driven CO_2(a) desorption channel. CO+O(a) reaction proceeds more easily with weakly-bound oxygen adatoms at the(111) terraces than strongly-bound oxygen adatoms at the(111) steps. These results reveal complex rate-limiting CO_2(a) desorption behaviors during CO+O(a) reaction on Au surfaces at low temperatures which provide novel information on the fundamental understanding of Au catalysis.
