Adsorption and Decomposition of NO on Magnesium Oxide: A Quantum Chemical Study

Embedded cluster model calculations based on density functional theory have been used to study the adsorption of NO on MgO surface. The calculation results indicate that at ideal terrace sites on MgO(100) surface, NO is weakly adsorbed as NO and cis -N 2 O 2, whereas at step and corner sites NO could be adsorbed as (a) NO adspecies with N-end bridging over the step-sitting Mg XC -O YC (X,Y = 3,4) ion pairs, (b) NO 2 2- adspecies with the O−N bond of the adsorbed NO molecule chaining over the step-sitting Mg XC -O YC (X,Y = 3,4) ion pairs, and (c) N 2 O 3 2- adspecies by attaching another NO molecule onto the NO 2 2- adspecies. The latter species could be regarded as an intermediate for NO decomposition over MgO catalyst. The calculated IR frequencies of the weakly adsorbed cis -N 2 O 2 species and the chemisorption-induced NO 2 2- and N 2 O 3 2- surface species agree well with those from the IR experiments. On the basis of the calculated energetics, a possible mechanism of NO decomposition reaction has been proposed.