Operando Observation of NO Reduction by CO on Ir(111) Surface Using NAP-XPS and Mass Spectrometry: Dominant Reaction Pathway to N2 Formation under Near Realistic Conditions

The nitric oxide (NO) reduction by carbon monoxide (CO) on Ir(111) surfaces under near ambient pressure conditions was studied by a combination of near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and mass spectrometry (MS), particularly paying attention to the dominant reaction pathway to formation of molecular nitrogen (N2). Under a relatively low CO pressure condition (50 mTorr NO + 10 mTorr CO), two reaction pathways to form N2 are clearly observed at different ignition temperatures (280 and 400 °C) and attributed to a reaction of NO adsorbed at atop site (NOatop) with atomic nitrogen (Nad) and associative desorption of Nad, respectively. Since the adsorption of NOatop is inhibited by CO adsorbed at atop site (COatop), the ignition of the NOatop + Nad reaction strongly depends on the coverage of COatop; the ignition temperature shifts to higher temperature as increasing CO pressure. In contrast, for the Nad + Nad reaction the ignition temperature keeps almost constant (∼400 °C). The onl...