posted on 2022-01-14, 21:29authored byZhiyuan Li, Na Li, Nan Wang, Bing Zhou, Pan Yin, Boyu Song, Jun Yu, Yusen Yang
Cu-based catalysts
are commonly applied in low-temperature water
gas shift (WGS) reactions, owing to their low cost and high catalytic
activity. The influence of different Cu surfaces on catalytic activity
and mechanism over the WGS reaction remains unclear. In this work,
the effect of different structures of surfaces on the WGS mechanism
is studied using density functional theory (DFT). Three surface terminations
(Cu(100), Cu(111), and Cu(211)) of Cu are considered, and the coordination
number (CN) of the active Cu site is in the range from 7 to 9. The
most stable surface is Cu(211). Then, d-band center values are calculated,
which decrease in the following sequence: Cu(211) > Cu(100) >
Cu(111).
This shows that d-band center values decrease with increasing coordination
number. The increase in the centers of the d-band leads to an increase
in the adsorption strength of CO and H2O adsorbates, which
is in line with the theory of the d-band center. In addition, the
further calculated mechanism for WGS reaction over three different
Cu surfaces illustrates that the carboxyl path is the most favorable
mechanism, and the rate-determining step is H2O dissociation.
Cu(211) shows excellent WGS catalytic performance, better than the
Cu(100) and Cu(111) surfaces. This work provides theoretical insights
into the rational design of highly active Cu-based catalysts toward
WGS reaction.