Insight into C + O(OH) reaction for carbon elimination on different types of CoNi(111) surfaces: a DFT study

Abstract

A density-functional theory (DFT) method has been performed to investigate the reaction of C + O(OH) on three types of bimetallic alloy CoNi(111) surface, and the results obtained are compared with those on the pure Ni(111) surface. Our results show that the introduction of Co into the Ni catalyst is beneficial for the adsorption of C, O and OH species, while it weakens the adsorption of CO. Moreover, O(OH) absorbs preferentially on the CoNi(111) surfaces with the surface enrichment of Co compared with the homogeneous CoNi(111) surface; the increased degree of O adsorption energy outweighs the corresponding values of C on the pure Ni(111) and three types of bimetallic alloy CoNi(111) surfaces, indicating that Co has a stronger affinity for oxygen species than for carbon species. On the other hand, the mechanism of the C + O(OH) reaction and the corresponding rate constants at different temperatures show that OH species have a stronger ability to eliminate carbon than O species on Ni(111) and CoNi(111) surfaces; on the CoNi(111) surface, when the Co surface coverage is equal to 1 monolayer (ML), compared to Ni(111), the C + O reaction can be accelerated. When the Co surface coverage is equal to 3/4 ML, the C + OH reaction is the most favorable; further, the rate constant for the C + OH reaction on a CoNi(111) with Co surface coverage of 3/4 ML is much larger than that of the C + O reaction on a CoNi(111) with Co surface coverage of 1 ML. As a result, for carbon elimination on the CoNi alloy surface, OH species should serve as the key species for carbon elimination, and the Co surface coverage of CoNi(111) surface should be kept at 3/4 ML.