Theoretical insights into the reaction mechanisms of NO oxidation catalyzed by Cu 2 O(1 1 1)

Abstract

• Cu 2 O shows superior catalytic activity toward NO oxidation. • Coadsorption of NO and O 2 gives rise to the formation of OONO species, which plays an important role in reducing barrier. • NO reacts with molecular or dissociated oxygen, rather than lattice oxygen of the Cu 2 O(1 1 1) surface. • NO 2 will poison the reaction of NO oxidation if it occurs through Langmuir–Hinshelwood mechanism, and an alternative Eley–Rideal mechanism makes NO 2 desorption possible. The NO oxidation on Cu 2 O(1 1 1) with molecular oxygen, dissociated oxygen, and lattice O, was studied by using periodic density functional theory. Cu 2 O could promote NO oxidation via the more favorable Elay–Rideal mechanism. For NO oxidation with molecular oxygen, path II (NO + O 2 * → O * ONO → NO 2 + O * ; NO + O* → NO 2 * → NO 2 ) was found as the most probable route, in which NO 2 desorption is the reaction rate determining step. The NO oxidation reaction with dissociated oxygen is also possible. In this case, O 2 dissociation occurs after surpassing a barrier of 105 kJ/mol. Thereafter, NO molecule can readily react with oxygen adatoms without barrier or with a moderate-low barrier of 49 kJ/mol. Both of the produced NO 2 molecules will release from the surface. The barrier to be surmounted is 53.3 and 103.2 kJ/mol, respectively. The reaction of NO with lattice O has a high barrier and it is very unlikely. The present results enrich our understanding of the catalytic oxidation of NO by metal-oxide catalysts.