Adsorption and dissociation of carbon monoxide on iron and iron-carbon clusters: Fe n + 2CO and Fe n C + 2CO, n = 4 and 7. A theoretical study

Abstract

Abstract In this work is studied the adsorption and reduction of carbon monoxide, CO, catalyzed by neutral and charged iron clusters, through the Fen0, ±1 + 2CO → FenC0, ±1 + CO2 (n = 4, 7) reactions in the gas phase. It was found, by means of all-electron density functional theory calculations, that the activation energy, Ea = 140 kcal/mol, for the Boudouard reaction, CO + CO → C + CO2, is considerably reduced, up to 33.6 and 58.2 kcal/mol, when the neutral Fe4 and Fe7 magnetic clusters acts as catalysts, respectively. Therefore, a primary role of Fen clusters is to decrease the barriers for dissociation of the CO molecule. For additional CO molecules reacting with the neutral products formed in the first reactions: the iron-carbon clusters Fe4C and Fe7C, results reveal that for the Fe4C + 2CO → Fe4C2 + CO2 process, the activation energy increases up to 44.7 kcal/mol. Notably, improvement in the catalytic behavior occurs for Fe7C since, for its correspondent reaction, it yields a smaller barrier, estimated as 44.8 kcal/mol. Low-lying states of charged Fe4 and Fe7 clusters interacting with CO molecules were characterized also. Overall, the neutral iron clusters produce smaller barrier energies than the charged Fe4,7±1 species.