Investigates the mechanism of Mn substitution effects on CO and H2O adsorption in various Fe3O4 facets, highlighting its implications for CO2 selectivity.
High CO 2 selectivity from the water–gas shift reaction (WGSR) limits carbon efficiency in iron-based Fischer–Tropsch synthesis. Mn promotion suppresses WGSR, but the mechanism remains unclear. Using DFT+ U, we studied how Mn substitution at octahedral Fe 2+ sites of Fe 3 O 4 affects CO/H 2 O adsorption on three facets: (111), (001), and (311). CO always prefers the (111)-Fe tet1 facet regardless of Mn concentration, confirming this facet as the CO activation site. At the optimal Mn coverage (θ Mn = 2/4 ML, 1.41 wt %), the (111)-Fe tet1 facet shows enhanced CO binding and weakened H 2 O adsorption. H 2 O shifts its preference with Mn loading: from (111) at low Mn to (311)-O above the optimal threshold (θ Mn = 2/4 ML). This Mn-induced spatial separation─CO fixed on (111), H 2 O diverted to (311)─suppresses the WGSR and lowers CO 2 selectivity without compromising CO activation. On the (001)-B facet, Mn weakens the adsorption of both molecules, making it less relevant. Based on these findings, we propose a facet-aware design principle: maximize (111) exposure with optimal Mn substitution and exploit Mn-induced CO/H 2 O segregation across facets to suppress the WGSR.
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Liu et al. (2026) studied this question.
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