Hydrogen-localization Transfer Regulation in 3D COFs Enhances Photocatalytic Acetylene Semi-hydrogenation to Ethylene

Abstract

In this work, a series of new crystalline three-dimensional covalent organic frameworks (3D COFs) based on [8+4] construction was designed and successfully realized efficient photocatalytic acetylene (C2H2) hydrogenation to ethylene (C2H4). By regulating the hydrogen-localization transfer effect in these 3D COFs，the Cz-Co-COF-H containing cobalt glyoximate active centers exhibited excellent C2H2-to-C2H4 performance, with an average C2H4 yield of 1755.33 μmol g-1 h-1 in pure C2H2, also showed near 100% conversion of C2H2 in 1% C2H2 contained crude C2H4 mixtures (industry-relevant conditions), and finally obtain polymer grade C2H4. In contrast, the Cz-Co-COF-BF2 only showed one fifth activity due to lack of hydrogen-localization transfer. The density functional theory (DFT), projected density of states (PDOS) and molecular dynamics "slow-growth" kinetic calculations based on precise 3D COF structures confirmed that the rapid hydrogen species transfer, enhanced water dissociation and suitable C2H2 adsorption in COFs jointly contributed efficient photocatalytic acetylene hydrogenation (PAH). This work provides new opportunity towards rational design and development of crystalline photocatalysts for C2H2 hydrogenation.