Mechanistic study of NO oxidation on Cr–phthalocyanine: theoretical insight

Abstract

The reaction mechanisms of NO oxidation on chromium–phthalocyanine (CrPc) were elucidated using density functional theory calculations and compared with NO reduction. The results reveal that the reaction of NO oxidation on CrPc is a two-consecutive step pathway which produces NO₂ as a product. The first step can proceed through competitive Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) mechanisms presenting the low activation barriers (E_a) in a range of 0.1 to 0.5 eV with exothermic aspects. Moreover, the ER mechanism is found to be more feasible. In the second step, the reaction requires an E_a of 0.32 eV, which is considered as the rate determining step of the overall reaction. By comparing both NO oxidation and reduction, the results reveal that in the low O₂ system, CrPc converts NO to N₂ via a dimer (NO)₂ mechanism whereas in the excess O₂ system, it oxidizes NO to NO₂ easily. Both reaction systems required very low E_a values, thus this low cost CrPc catalyst could be a candidate for NO treatment at room temperature.