Mechanistic Insights on the Low-Temperature Oxidation of CO Catalyzed by Isolated Co Ions in N-Doped Carbon
Colby A. Whitcomb, Anna Sviripa, Michael I. Schapowal, Konstantin Mamedov, Raymond R. Unocic, Christopher Paolucci, Robert J. Davis
Abstract
Isolated cobalt ions on nitrogen-doped carbon (Co–N–C) catalyze CO oxidation at temperatures as low as 196 K, but the active site and mechanism for this reaction remain elusive. In this work, steady-state CO oxidation around 273 K over Co–N–C revealed nearly first-order behavior in both CO and O2 as well as a negative apparent activation energy. Isotopic transient analysis of the reaction confirmed a rapid turnover frequency and low surface coverage of adsorbed intermediates leading to CO2 (<10% of the Co). Results from kinetics experiments combined with quantum chemical calculations and molecular dynamics simulations are consistent with a reaction path involving weak adsorption of CO onto Co ions followed by a low barrier for the CO-assisted activation of weakly adsorbed O2. This proposed mechanism for dioxygen activation does not involve a redox cycle with the transition-metal ion and may be important in other low-temperature catalytic reactions involving O2.