Synergic effects between boron and nitrogen atoms in BN-codoped C59- n BN n fullerenes (n = 1-3) for metal-free reduction of greenhouse N2O gas

Abstract

The geometries, electronic structures, and catalytic properties of BN-codoped fullerenes C_59-n BN _n (n = 1-3) are studied using first-principles computations. The results showed that BN-codoping can significantly modify the properties of C₆₀ fullerene by breaking local charge neutrality and creating active sites. The codoping of B and N enhances the formation energy of fullerenes, indicating that the synergistic effects of these atoms helps to stabilize the C_59-n BN _n structures. The stepwise addition of N atoms around the B atom improves catalytic activities of C_59-n BN _n in N₂O reduction. The reduction of N₂O over C₅₈BN and C₅₇BN₂ begins with its chemisorption on the B-C bond of the fullerene, followed by the concerted interaction of CO with N₂O and the release of N₂. The resulting OCO intermediate is subsequently transformed into a CO₂ molecule, which is weakly adsorbed on the B atom of the fullerene. On the contrary, nitrogen-rich C₅₆BN₃ fullerene is found to decompose N₂O into N₂ and O* species without the requirement for activation energy. The CO molecule then removes the O* species with a low activation barrier. The activation barrier of the N₂O reduction on C₅₆BN₃ fullerene is just 0.28 eV, which is lower than that of noble metals.

Fig. 1. Local atomic structures (left) molecular electrostatic potential isosurfaces (MEP, middle) and TDOS plots (right) of (a) C₆₀, (b) C₅₉B, (c) C₅₈BN, (d) C₅₇BN₂ and (e) C₅₆BN₃. The dashed line in TDOS plots shows the Fermi level. The color range in the MEP maps is from blue (more negative = −0.001 a.u.) to red (more positive = 0.078 a.u.).

Fig. 2. The optimized local atomic structures, key bond lengths (in Å), and PDOS plots of N₂O adsorbed onto (a) C₅₉B, (b) C₅₈BN, (c) C₅₇BN₂ and (d) C₅₆BN₃ fullerenes. In the PDOS plots, the Fermi level is indicated by the dashed line.

Fig. 3. The optimized local atomic structures, binding distances (in Å), and PDOS plots of CO adsorbed onto (a) C₅₉B, (b) C₅₈BN, (c) C₅₇BN₂ and (d) C₅₆BN₃ fullerenes. In the PDOS plots, the Fermi level is indicated by the dashed line.

Fig. 4. The potential energy diagram and relevant bond distances (in Å) for direct decomposition of N₂O over (a) C₅₈BN and (b) C₅₇BN₂ fullerenes.

Fig. 5. The potential energy diagram and relevant bond distances (in Å) for removing O* atom by CO over (a) C₅₈BN, (b) C₅₇BN₂ and (c) C₅₆BN₃ fullerenes.

Fig. 6. The potential energy diagram and relevant bond distances (in Å) for reduction of N₂O by CO molecule through the L–H mechanism over (a) C₅₈BN and (b) C₅₇BN₂ fullerenes.