First-principles study of CO catalytic oxidation on Pd-doped single wall boron nitride nanotube

Abstract

The carbon monoxide (CO) catalytic oxidation reaction is a model reaction which is important in serials of technical and industrial applications. In this study, density functional theory (DFT) is employed to explore the catalytic oxidation of CO on Pd-doped boron nitride nanotube (BNNT). The electronic structures and thermodynamic parameters of CO and O2, which are adsorbed on BNNT substrate with Pd embedded at the N- and B- vacancy, are examined in detail. It is revealed that the BNNT substrate with vacancy strongly stabilizes the Pd adatom. Benefit from the B vacancy defect, the Pd atom binds strongly with BNNT. The interaction energy of 3.74eV is strong enough to prevent the aggregation of Pd atom. With B vacancy, Pd atom accepts extra electron from the substrate, causing O2 to bind stronger than CO molecule. An additional charge is transferred to O2 when CO and O2 are co-adsorbed on the substrate. This additional charge thus strengthens the O2 and CO adsorption and changes the electronic structure properties of the tube. Four proposed CO oxidation mechanisms (Eley–Rideal (ER), Langmuir–Hinshelwood (LH), termolecular Eley–Rideal (TER), and termolecular Langmuir–Hinshelwood (TLH)) are studied by calculating the reaction energy barriers along the minimum-energy pathway. It is found that a large reaction barrier exists in the rate-limiting step of the ER mechanism. It is then suggested that the most probable mechanisms for CO oxidation on Pd doped boron vacancy BNNT (Pd-Bv/BNNT) could be the LH mechanism and the new TER and TLH mechanisms under experimental circumstances.