Activation and Coupling: First Principles. Selectivity of the Catalyst

Transcription

1 Supporting Information Subsurface Boron Doped Copper for Methane Activation and Coupling: First Principles Investigation of the Structure, Activity and Selectivity of the Catalyst Quang Thang Trinh, 1 Arghya Banerjee, 2 Yanhui Yang, 1,2 Samir H. Mushrif 1,2,* 1 Cambridge Centre for Advanced Research and Education in Singapore (CARES), Nanyang Technological University, 1 Create Way, Singapore , Singapore. 2 School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore , Singapore. Corresponding Author * address: SHMushrif@ntu.edu.sg (SHM) S1

2 Figure S1. F4 and B5 step sites on a model of p(4 8) Cu(111) unit cell with three missing rows on the top layer S2

3 Table T1. Free energy for the diffusion from on-surface site to sub-surface site of single B atom at temperature of 500 K and 1363 K. Metal Temperature (K) E (kj/mol) ZPE (kj/mol) H cor (kj/mol) T S (kj/mol) G (kj/mol) Cu Ni Pd Co S3

4 Figure S2. Transition states and diffusion barrier for the diffusion of Boron inside Cu(111) lattice: a) diffusion of B from on-surface to sub-surface octahedral site. b) Diffusion of B from first sub-surface octahedral site to deeper second sub-surface octahedral site. c) Horizontal diffusion from sub-surface octahedral sites within the first sub-surface layer. Dash circles illustrate Boron atoms at the beginning and end positions and the arrows indicate the diffusion direction. S4

5 Table T2. Average binding energy (kj/mol) of subsurface B at different coverages relative to the binding energy of 1/16 ML B subsurface obtained from PBE and optb88-vdw functionals Functional 1/16 B subsurface 2/16 ML B subsurface 4/16 ML B subsurface 1ML B Far Near Far Near subsurface PBE optb88-vdw S5

6 Figure S3. Diffusion of B from 1ML subsurface layer to the 2 nd subsurface layer. The diffusing atom is highlighted with yellow color. S6

7 Stability of different structures of Boron in Cu at different coverages. Actually at different dosage of B and at different temperatures (the influence of pressure is not considered and taken the value of 1atm in our study), the most stable structure might be different. To evaluate this, we computed the stabilities of different structures of B on Cu(111) surface as the free energy per Boron atom referenced to the clean Cu slab and B 2 H 6 (diborane) from the reaction: This procedure is widely used to evaluate the stabilities of different structures of B when doped with other transition metals such as Ni-B (Xu et al., The Journal of Physical Chemistry C 2009, 113, 4099), Co-B (Tan et al., Journal of Catalysis 2011, 280, 50) and Pd-B (Yoo et al., ACS Catalysis 2015, 5, 6579). The usage of B 2 H 6 as the source of B is due to the fact that B 2 H 6 is usually more stable than H 3 BO 3 under the reaction conditions (Tan et al., Journal of Catalysis 2011, 280, 50). Different structures of B in Cu slab were evaluated include the on-surface structures and sub-surface structures at different coverages of 0.25 ML, 0.5 ML, 0.75 ML and 1 ML. For those structures, p(2 2 4) slab of Cu(111) was used. At 0.5 ML, another structure was also considered include the reconstructed p4g clock Copper boride and the structure of p(2 8) unit cell of Cu with two missing rows on the top layer was used (similar to the model illustrated in Figure S1, Supporting Information). Those structures are presented in Figure S3. Figure S4. Different structures of B doped with Cu at different B coverages. a) 0.25 ML onsurface B; b) 0.5 ML on-surface B; c) 0.75 ML on-surface B; d) 1 ML on-surface B; e) p4g clock boride; f) 0.25 ML subsurface B; g) 0.5 ML subsurface B; h) 0.75 ML subsurface B and i) 1 ML subsurface B. The unit cell of p(2 2) was also indicated in Figs. S6a-d and S6f-i. Similarly to the calculations of stabilities of surface intermediates, all the thermodynamics properties was computed involve the Zero point energies (ZPEs), entropy and enthalpy correction. The harmonic vibrational simulations was conducted for the top layer of Cu and all B atoms in the structures are allowed to be relaxed. For the gas components (B 2 H 6 and H 2 ), all those properties are obtained from the standard thermodynamics NIST-JANAF table. We have also calculated the stabilities of all different structures of B in Cu at three temperature conditions of the reaction, 1223K, 1323K and 1363 K. S7

8 Figure S5. Optimized adsorption site and structures of intermediates forming on the surface of B-Cu catalyst during methane activation process. S8

9 Figure S6. Transition state and activation barrier of C-H activations processed at a Cu 2 u site of B-Cu catalyst: a) CH 3 CH 2 + H and b) CH 2 CH + H. Those barriers are much higher than the corresponding barriers computed at the Cu 4 u site of B-Cu catalyst as presented in the main text. S9

10 Figure S7. Transition state and activation barrier for the C-C coupling of CH 2 and CH 3 fragments forming C 2 H 5 processed at Cu 2 u site of B-Cu catalyst. This barrier is also much higher than the corresponding barrier computed at Cu 4 u site of B-Cu catalyst (129 kj/mol) as presented in the main text S10

11 Figure S8. a) Activation of methane nearby existing CH 3 fragment on a Cu 4 u and b) on a Cu 2 u site. C) Activation of methane nearby existing CH2 fragment on a Cu 4 u and d) on a Cu 2 u site. S11

12 Figure S9. Transition states and activation barriers for the dehydrogenation of a) C 2 H 5 C 2 H 4 + H and b) C 2 H 4 C 2 H 3 + H on the surface of B-Cu. S12