Mechanism of methylene oxidation on Pt catalysts: A DFT study

Abstract

Methane activation on catalysts is important in several applications such as catalytic combustion of natural gas. In order to explore the mechanism of methane catalytic combustion from the atomic scale, the quantum chemical study of methylene oxidation on Pt catalysts was conducted based on density functional theory in this paper. The rate-limiting step for the pathway from methylene to carbon monoxide is the formaldehyde oxidizing into aldehyde, which has a high activation energy of 175.26kJ/mol and a low reaction rate constant of 3.971E+04s−1. Subsequently, the reaction of aldehyde further oxidizing into carbon monoxide is easy to proceed. Finally, there are two different oxidation pathways of CO into CO2: ①CO(s)+O(s)→CO2+Pt, ②CO(s)+OH(s)→CO2+H(s). The former pathway is totally exothermic by 49.41kJ/mol while the latter releases more heat value of 58.54kJ/mol. In addition, the pathway② requires a lower activation energy and has a much higher reaction rate constant than the pathway①. Consequently, pathway② is the dominant step. The major reaction pathway during the methylene oxidation follows: CH2→HCHO→CHO→CO→COOH→CO2. The prior reaction pathway of water generation is OH(s)+OH(s)→H2O+O(s).