Interactive Surface Chemistry of CO2 and NO2 on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

Interactive surface chemistry of CO 2 and NO 2 on BaO x /Pt(111) model catalyst surfaces were investigated via X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques with a particular emphasis on the competition between different adsorbates for the catalytic adsorption sites and adsorbate-induced morphological changes. After NO 2 adsorption, nitrated BaO x /Pt(111) surfaces do not reveal available adsorption sites for CO 2 at 323 K, irrespective of the presence/absence of exposed Pt sites on the surface. Although NO 2 adsorption on thick BaO x (>10MLE)/Pt(111) overlayers at 323 K leads to the formation of predominantly nitrate species, NO 2 adsorption on the corresponding carbonated surface leads to the formation of coexisting nitrates and nitrites. The presence of carbonates on BaO x /Pt(111) overlayers does not prevent NO 2 uptake. Carbonated BaO x (1.5 MLE)/Pt(111) surfaces (with exposed Pt sites) obtained via CO 2 adsorption can also further interact with NO 2, forming surface nitrate/nitrite species, accompanied by the transformation of surface carbonates into bulk carbonate species. These results suggest that the nitrate formation process requires the presence of two adjacent unoccupied adsorption sites. It is apparent that in the presence of both NO 2 and CO 2, carbonate species formed on Lewis base (O 2– ) sites enable the formation of nitrites on Lewis acid (Ba 2+ ) sites. Thermal aging, nitration, and carbonation have a direct impact on the morphology of the two-/three-dimensional (2D/3D) BaO x aggregates on Pt(111). While thermal aging in vacuum leads to the sintering of the BaO x domains, nitration and carbonation results in redispersion and spreading of the BaO x domains on the Pt(111) substrate.