Can Si-embedded boron nitride nanotubes act as a favorable metal-free catalyst for CO oxidation by N2O?

Abstract

The oxidation of carbon monoxide (CO) as a toxic gas has a significant role in solving environmental problems and is important for a series of technological applications. In this paper, the oxidation of CO with N₂O molecule is studied over Si-doped (6,0) boron nitride nanotubes (Si–BNNTs) by means of density functional theory calculations. Also, reaction barriers and thermodynamic parameters are calculated using the M06-2X density functional with 6-31G* basis set. Si-doping of the BNNT at two possible substitution sites are explored, i.e. a boron site (Si_B) or a nitrogen site (Si_N). In both cases, the Si atom is found to be stabilized above the vacancy site after geometry relaxation. Also, the effects of increasing the tube length on the adsorption of gas molecules and CO oxidation reaction are studied in detail. Results show that the CO oxidation catalyzed by the Si–BNNTs is likely to occur at the room temperature. Besides, the Si_B substrate shows a better reactivity toward the CO oxidation due to its first barrier-less pathway and lower activation energy in second route (1.78 kcal mol⁻¹) than that in Si_N (9.75 kcal mol⁻¹).