Adsorption kinetics and dynamics of CO, NO, and CO2 on reduced CaO(100)

The adsorption kinetics and dynamics of typical combustion gases have been studied on CaO(100) by means of temperature programmed desorption and molecular beam scattering. In addition, the sample has been characterized by Auger electron spectroscopy. Whereas CO interacts rather weakly with CaO and adsorbs molecularly on pristine and oxygen vacancy sites, CO2 and NO interact strongly with CaO, leading to a variety of structures in TPD. CO2 adsorption leads to the formation of carbonates. NO adsorption results in the desorption of N-2 and N2O species presumably by the formation of NO dimers stabilized at defect sites, which is consistent with prior reports. In assisting the assignment of the TPD structures that have been seen, density functional cluster calculations have been performed and are compared with results from prior studies. Trends seen for the initial adsorption probabilities, S-0, are consistent with a simple mass-match model, S-0-CO > S-0-CO2. The coverage dependence of the adsorption dynamics is dominated by precursor effects for CO2 but shows direct Langmuirian adsorption dynamics of CO.