Design of Frustrated Lewis Pairs by Functionalizing N-Doped Graphene Edge with Tunable Activity for H₂ Dissociation

Abstract

While the frustrated Lewis pair (FLP) concept has been successfully extended to heterogeneous catalysis, the underlying factors governing the catalytic performances of FLPs and designing strategies remain elusive. Herein, a theoretical study is performed to design metal-free heterogeneous FLPs with tunable activity for hydrogen dissociation. The designed FLPs constructed by functionalizing the N-doped zigzag graphene edge with eight functional groups −BX2 (X = F, Cl, Br, H, CH3, CF3, CN, NO2) can readily heterolytically dissociate H2 (H2 → Hδ− + Hδ+) with reaction barriers varying from 0.15 to 0.70 eV, showing their comparable activity to homogeneous FLPs. More importantly, FLP acidities of designed FLPs are linearly correlated with the reaction energies of H2 dissociation, suggesting the significant role of FLP acidity in determining their catalytic activity. Further calculations show that the reaction barriers of hydrogenation of CO2 also linearly correlate with the reaction energies of H2 dissociation and accordingly are governed by FLP acidity. Overall, this study provides a route for designing metal-free heterogeneous FLPs on graphene materials and discloses a close relationship between the composition (N···BX2), the electronic structure (FLP acidity), and the functionality (catalytic ability) of the FLPs.

Theoretical Perspective on the Design of Surface Frustrated Lewis Pairs for Small-Molecule Activation

“…Besides the common hydroxyl group on metal oxides, the hydroxyl group on boron nitride, and the organic functional groups containing acid sites or basic sites binding to the surfaces, such as graphene and metal–organic frameworks (MOF), can also generate surface FLP to activate small molecules effectively. A series of computational studies since 2015 have proposed strategies for designing surface FLP by adding the Lewis pairs functional groups to the porous MOF for CO 2 hydrogenation. , As shown in Figure c, the molecule [1-(difluoroboranyl)-4-methyl-1H-pyrazole] named as P-BF 2 binds to the UiO-66, and thus, the Lewis acid (B) and base (N b ) sites of the P-BF 2 form the surface FLP to activate H 2 and CO 2 molecules effectively .…”

“…Similarly, the phosphorene doped with B or Al atoms is predicted to generate surface FLP for hydrogen activation . In comparison with metal oxides, the 2D materials possess a large surface area and rich surface chemistry, which are more prone to increase the number of surface sites and adjust the acidity and basicity of the surface FLP to achieve better reaction performance . Overall, introducing surface heteroatoms directly forming SFLP or indirectly contributing to SFLP formation provides broader practical methods for constructing SFLP sites on various materials in the future and also a flexible way to adjust the acidity and basicity of SFLP for small-molecule activation.…”

Electron delocalization in defect-containing graphene and its influence on tetrel bond formation

“…3,4,10,11 Moreover, it is known that the simultaneous coexistence of sterically hindered Lewis acids and Lewis bases within one material promotes its catalytic activity towards H 2 activation. 12,13 According to the general understanding of frustrated Lewis pairs in graphene, 14–16 to obtain a frustrated Lewis pair in graphene usually requires doping with N or P atoms to form the centres of the Lewis bases and with various carriers of B, Al, or Ga atoms as the Lewis acids. The emergence of these active sites due to point defects in graphene demonstrates its high chemical potential for use in catalytic processes.…”