First-Principles Characterization of NO_x Adsorption on MgO

Abstract

Alkaline earth oxides are leading candidates as NO x (x = 1, 2) sorbents; however, the understanding of adsorption and reaction of NO x on these surfaces is currently limited. In this paper, Mg(001) terrace cluster models and density functional theory (DFT) are used to characterize the adsorption properties of neutral and charged NO, NO2, and NO3. Neutral NO and NO2 molecules weakly adsorb on the MgO terrace, while neutral NO3 adsorbs more strongly through oxidation and significant acid−base coordination with the surface. Chemisorbed nitrite can be formed either from adsorption of Lewis acidic NO+ on Lewis base surface sites (Os 2-) or from adsorption of Lewis basic NO2 - on Lewis acid surface sites (Mgs 2+). Similarly, chemisorbed nitrate can form from NO2 + adsorption on Os 2- sites or NO3 - adsorption on Mgs 2+ sites. These charged adsorbates are not expected to exist in isolation on the MgO surface but rather are expected to form oppositely charged, cooperatively bound pairs with enhanced adsorption energy over the isolated neutrals. While results are demonstrated for adsorption on MgO, they have application to NO x adsorption on a wide range of oxide surfaces.

Periodic DFT Study of Acidic Trace Atmospheric Gas Molecule Adsorption on Ca- and Fe-Doped MgO(001) Surface Basic Sites

“…This interaction was reported to have a low adsorption energy of −10.2 kcal/mol and a large surface-adsorbate separation of 2.62 Å using PW91 functional. 24 Our calculated value of −0.19 kcal/mol reported in Table 3 shows no interaction between the NO 2 molecule and the surface, consistent with the rich NO 2 coordination chemistry reported earlier. 59 The magnitude of this interaction can be described as physisorption, well in agreement with experimental observations where adsorbed NO 2 was only transformed into nitrate at elevated temperatures.…”

Probing the Surface of Ceria−Zirconia Catalysts Using NOx Adsorption/Desorption: A First Step Toward the Investigation of Crystallite Heterogeneity

“…14 By contrast, at low coordinated pair sites on steps and corners, activated sorption could take place as NO -or NO 2 -species and this process predominates above room temperature. 13,14,17,18 For the sake of brevity, the whole set of time-resolved DRIFTS spectra is only presented for CeO 2 , which presents the most resolved spectral features ( Figure 3). By contrast, ceria-zirconia catalysts displayed more blurred spectral features due to surface heterogeneity.…”

Interaction of sulfur dioxide with titanium–carbide nanoparticles and surfaces: A density functional study

“…[38][39][40][41] This code allows a systematic treatment of molecules and periodic systems. [38][39][40][41] In test calculations for S/TiC͑001͒ we found identical trends in the relative stability of adsorption sites with DMOL 3 and CASTEP ͑plane-wave basis set, pseudopotentials to treat the core levels͒, 13,17 obtaining similar energetics and geometries. Here, all the electron of C, O, S, and Ti were included in the calculations explicitly.…”