Effect of metal catalyst on the mechanism of hydrogen spillover in three-dimensional covalent-organi

• 作 者: 刘秀英 于景新 李晓东 刘桂成 李晓凤 Joong-Kee Lee
• 机 构: College of Science,Henan University of Technology,Center for Energy Convergence Research,Green City
• 出 处: Chinese Physics B
• 发表日期: 2017年02期
• 关键词: migration covalent migrate contrary spontaneously systematically toward prefer s

Hydrogen spillover mechanism of metal-supported covalent-organic frameworks COF-105 is investigated by means of the density functional theory, and the effects of metal catalysts M_4(Pt_4, Pd_4, and Ni_4) on the whole spillover process are systematically analyzed. These three metal catalysts exhibit several similar phenomena:(i) they prefer to deposit on the tetra(_4-dihydroxyborylphenyl) silane(TBPS) cluster with surface-contacted configuration;(ii) only the H atoms at the bridge site can migrate to 2,3,6,7,10,11-hexahydroxy triphenylene(HHTP) and TBPS surfaces, and the migration process is an endothermic reaction and not stable;(iii) the introduction of M_4 catalyst can greatly reduce the diffusion energy barrier of H atoms, which makes it easier for the H atoms to diffuse on the substrate surface. Differently, all of the H2 molecules spontaneously dissociate into H atoms onto Pt_4 and Pd_4clusters. However, the adsorbed H2 molecules on Ni_4 cluster show two types of adsorption states: one activated state with stretched H–H bond length of 0.88 ?A via the Kubas interaction and five dissociated states with separated hydrogen atoms. Among all the M_4 catalysts, the orders of the binding energy of M_4 deposited on the substrate and average chemisorption energy per H2 molecule are Pt_4>Ni_4>Pd_4. On the contrary, the orders of the migration and diffusion barriers of H atoms are Pt_4 Ni_4> Pd_4. On the contrary, the orders of the migration and diffusion barriers of H atoms are Pt_4