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The surface phase structure evolution of the fcc MoC (001) surface in a steam reforming atmosphere: systematic kinetic and thermodynamic investigations
The kinetic and thermodynamic aspects of the surface phase structure evolution of an fcc MoC (001) surface under a H 2 O/H 2 -rich atmosphere typically found during steam reforming processes were systematically studied via periodic density functional theory (DFT) and ab initio thermodynamic methods....
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| Published in: | Catalysis science & technology 2022-02, Vol.12 (4), p.113-1143 |
|---|---|
| Main Authors: | , , , , , , , , |
| Format: | Article |
| Language: | English |
| Subjects: | |
| Citations: | Items that this one cites Items that cite this one |
| Online Access: | Get full text |
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| Summary: | The kinetic and thermodynamic aspects of the surface phase structure evolution of an fcc MoC (001) surface under a H
2
O/H
2
-rich atmosphere typically found during steam reforming processes were systematically studied
via
periodic density functional theory (DFT) and
ab initio
thermodynamic methods. The various stable configurations of surface species (H
2
O*, OH*, O*,
, and H*) at different coverages and their formation rates considering different coverage effects of certain species were explored. At a molecular H
2
O* adsorption coverage (
H
2
O
) ≤1/3 ML, the adsorption of H
2
O mainly takes place through single Mo-O coordination, while the capture of H
2
O above 1/3 ML relies on hydrogen bonds. H
2
O* dissociation resulting in OH* formation is always facile at different H
2
O* coverages, whereas it becomes unfavourable as the OH* coverage increases beyond 4/9 ML due to unavoidable strong hydrogen bond breaking. Surface O* can be easily formed
via
hydroxyl disproportionation with negligible energy barriers, and the protonation of O* by H
2
O* is also facile. The dissociation of
will easily generate surface Mo-H* and C-H* species, where Mo-H* can readily transform to C-H* with significant exothermicity. The average surface binding strengths of various species at 0 K follow the order: H
2
O* > H* OH* >
> O*, where the average binding strength of O* becomes positive when
O*
≥ 1/3 ML. At 473.15 K and over a wide H
2
O pressure range, mixtures of H
2
O*, OH*, and O* are the predominant species on the (001) surface, highlighting the role of the (001) surface in steam reforming reactions, while H* species only emerge at low H
2
O pressure or high H
2
pressure. The proportion of O* species decreases and finally tends to zero as the H
2
pressure increases from 10
−10
to 10
−7
MPa, while the proportion of OH* species increases due to O* protonation. As the H
2
pressure increases from 10
−7
to 10 MPa, the proportion of OH* species decreased, accompanied by an increase in the H
2
O coverage. As the H
2
O pressure decreased, the stable existence of surface H* species became increasingly more favorable, and the emergence of surface H* species was accompanied by the disappearance of surface O-containing species, changing the catalytic role of the (001) surface from catalyzing steam reforming processes to promoting hydrogenation reactions.
Systematic
ab initio
-based calculations were performed to clarify the surface structure evolution of the fcc MoC (001) surface at |
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| ISSN: | 2044-4753 2044-4761 |
| DOI: | 10.1039/d1cy01554k |