Strong chemisorption of CO₂ on B₁₀–B₁₃ planar-type clusters

Abstract

An ab initio density functional study was performed investigating the adsorption of CO 2 on the neutral boron B n (n = 10 − 13) clusters, characterized by planar and quasiplanar ground-state atomic structures. For all four clusters, we found strong chemisorption energy of CO 2 reaching 1.6 eV for B 12 at the cluster edge sites with the adsorbed molecule in the plane of the cluster.A configuration with chemisorbed dissociated CO 2 molecule also exists for B 11 and B 13 clusters.The strong adsorption is due to the bending of the CO 2 molecule, which provides energetically accessible fully in-plane frontier molecular orbitals matching the edge states of the clusters. At the same time, the intrinsic dipole moment of a bent CO 2 molecule facilitates the transfer of excess electronic charge from the cluster edges to the molecule.

Selective capture of CO2 over N2 and CH4: B clusters and their size effects

“…The (initially linear) CO 2 molecule bends at an angle of 122 • as it chemisorbs on the B 12 cluster, which corresponds to the equilibrium geometry predicted for the negatively charged CO 2 molecule [34]. We note that the strong chemisorption of CO 2 on B 12 is also robust within the GGA+U approach, which increases the CO 2 HOMO-LUMO band gap [14].…”

“…We attribute thus the much higher reactivity of B 8 (leading to dissociated adsorption of CO 2 ) predominantly to its near orbital degeneracy. In fact, it should be noted that the other B clusters for which we found earlier [14] dissociated adsorption of CO 2 , i.e., factor, however, we also observe an overall smoother general tendency of decreasing binding energy |E ads | of the adsorbed molecules with increasing size of the B clusters, as will be illustrated in the next section.…”

“…+0.01 −0.58 [33] C-B 4.47 -For the chemisorbed B 12 -CO 2 system, the adsorbed CO 2 molecule lies in the plane of the cluster (Figure 1a). This favors strong interaction between the in-plane lowest unoccupied molecular orbital (LUMO) of the bent CO 2 and the in-plane high-energy occupied molecular orbitals of the B cluster [14]. The O-B and C-B distances are found to be 1.4 and 1.6Å, respectively.…”

“…In Figure 3, we show the available lowest-energy data from GGA/DFT calculations (B3LYP calculations for N 2 on B 36 ) obtained for each of the three molecules on the B n planar-type clusters, as a function of inverse cluster size 1/n. Apart from the results for the three molecules on B 8 and B 12 , we also included the lowest E ads values for CO 2 on the B 10 , B 11 , B 13 and on the semi-infinite B sheet (n → ∞) from our previous calculations [14] and the value of Ref. 26 for the adsorption of N 2 on the planar-type B 36 cluster.…”

“…This requires, in particular, a strong adsorption energy, whose magnitude should typically overcome that of the standard free energy of gaseous CO 2 at 300 K (0.67 eV) [13]. A number of recent theoretical studies have revealed potentially interesting chemisorption properties of CO 2 on Boron-based clusters and related model solid surfaces [9][10][11][12][14][15][16]. Small Boron clusters, containing 13 or less atoms, have been shown both experimentally and theoretically to be planar or quasiplanar [17][18][19][20], while a number of medium size clusters (up to ∼ 40 atoms) are also expected to occur in planar-type structures on the basis of available experimental and/or theoretical studies [21][22][23][24][25].…”