Atomic-level mechanism and microkinetics of HCHO oxidation over K-doped MnO2 catalysts

Abstract

K-doped MnO2 is regarded as an efficient catalyst for HCHO oxidation. A combined study of density functional theory (DFT) and microkinetic modeling was implemented to investigate the role of potassium doping in the catalytic reactivity of MnO2 towards HCHO oxidation. The DFT-derived thermodynamic stability analysis indicates that the K-doped MnO2 surface is more stable than the pristine MnO2 surface under the practical experimental conditions. The introduction of K ion is energetically beneficial to the adsorption of HCHO and O2 by charge transfer from potassium to the catalyst surface. The HCHO oxidation paths show that the rate-determining step is the second dehydrogenation reaction. The best catalytic activity of MnO2@K-1 is associated with the abundant Mn atom with a high chemical valence on the catalyst surface. Specially, K doping has little effect on the adsorption of water, but promotes the production of OH group by reducing the energy barrier of hydrolysis. The hydroxylated surface is favorable for the two-step cleavage of the C-H bond. The overall reaction rate of HCHO oxidation on the K-doped MnO2 catalyst is much higher than that on the pristine MnO2. At low temperatures, the reaction rate is relatively insensitive to the pressure change, while the oxidation rate gradually rises with the increasing of pressure at high temperatures. K doping is conducive to boosting the reaction rate of HCHO oxidation, which is associated with the stronger interaction of reactants with K-doped catalysts.