Mechanism insights into direct conversion of syngas into C2 oxygenates via key intermediate C2O2 over Ni-Supported graphene

Abstract

A critical step toward the rational design of new catalyst that achieve selective and efficient synthesis of C2+ oxygenates from syngas (CO/H2) by Fischer-Tropsch synthesis (FTS) is to determine the detailed reaction mechanism. Herein, the mechanism of two gaseous CO monomers coupling into a chemisorbed ethylene dione (O∗C∗CO) and subsequent hydrogenation of O∗C∗CO on the chainmail catalyst of nickel-supported graphene surface is reported. The results show that two gaseous CO monomers can be coupled into a two-atom-chemisorbed O∗C∗CO via a metastable intermediate of O∗CCO single-atom-chemisorbed on Ni-supported on graphene with the barrier energy of 0.85 eV and a strong exothermicity of 1.45 eV. The key intermediate of O∗C∗CO can be stably chemisorbed on the Ni-supported-graphene surface by riveting two coupled C atoms on the ortho-, meta-, or para-position of graphene six-membered ring, forming four-, five-, and six-membered ring with the carbon atoms of graphene, respectively. Then, the potential energy surfaces of chemisorbed O∗C∗CO hydrogenation indicates that glycol-aldehyde (HOH2C–CHO) would be preferred to form by the kinetically favorable initial C-hydrogenation due to the low rate-limiting barrier of 0.46 eV, while the glyoxal (OHC=CHO) is a considerably competitive product because its rate-limiting barrier is only 0.18 eV higher than that of the glycol-aldehyde. These results suggest that the chainmail catalyst of nickel-supported graphene could be a potential and high-efficient catalyst for synthesis of C2 oxygenates from syngas, which also provides a fundamental insight into the new reaction mechanism of Fischer-Tropsch synthesis.