First-Principles Study on Oxidation of Methane to Methanol Catalyzed by Non-Stoichiometric Tungsten Oxide （WO3-x）

doi:10.16553/j.cnki.issn1000-985x.2025.0035

Abstract

Abstract: The key challenge in the oxidation of methane to methanol is attributed to the efficient activation of CH₄ by catalysts. Non-stoichiometric WO_3-_x （0<x<3）， recognized for its controllable oxygen vacancies along with structural stability and conductive advantages， has emerged as a research hotspot in novel catalytic materials. In this study， density functional theory （DFT） methods were employed to systematically investigate the catalytic performance of six distinct WO_3-_x materials for oxidation of methane to methanol. The mechanisms were elucidated through comprehensive analyses of material structures， surface active sites， methane oxidation behaviors and electronic properties. The results reveal that the WO-terminated surface of the WO_2.72 catalyst demonstrates enhanced methane adsorption and activation capabilities， which are ascribed to its lower work function， hybridization between W 5d orbitals and CH₄ molecules， and the strong electron-donating capacity of W atomic states. Specifically， this surface exhibits a favorable CH₄ adsorption free energy （-0.62 eV） and dissociation free energy （-0.07 eV）. These findings provide theoretical guidance for exploring the application of WO_3-_x catalysts in methane oxidation reactions.

Key words: methane; photocatalysis; WO_3-_x; first-principle; density functional theory

CLC Number:

O469

QIN Jilong, LI Xiangyuan, ZHANG Lulu, LIU Jianxin, LI Rui. First-Principles Study on Oxidation of Methane to Methanol Catalyzed by Non-Stoichiometric Tungsten Oxide （WO_3-_x）[J]. Journal of Synthetic Crystals, 2025, 54(8): 1441-1453.

Figures/Tables 14

Fig.1 Crystal model used in this paper

Fig.2 Projected band structures （left） and projected density of states （right）

Table 1 Surface energy parameters for two terms of WO3-x

Surface energy， γ/（eV·Å^-2）	WO₃	WO_2.9	WO_2.72	WO_2.67	WO_2.63	WO₂
WO term	0.030 4	0.045 7	0.060 2	0.077 2	0.079 8	0.080 9
O term	0.084 8	0.102 3	0.112 5	0.081 2	0.082 7	0.123 9

Fig.3 Work functions of the WO （left） and O （right） terms

Fig.4 Partial charge densities in the valence and conduction bands for two terms of WO3-x

Fig.5 Adsorption energy of methane on different sites of catalysts

Table 2 Adsorption energy and structural parameters of CH4 on the WO3-x surface

Parameter	WO₃	WO_2.9	WO_2.72	WO_2.67	WO_2.63	WO₂
E_ads/eV	-0.460 0	-0.211 0	-1.001 0	-0.461 0	-0.515 0	-0.348 0
d_（C—H）/Å	1.095 8	1.096 1	1.101 2	1.098 6	1.097 7	1.101 3
d/Å	2.652 0	2.787 0	2.134 3	2.664 0	2.592 0	2.750 3

Fig.6 WO3-x Bader charge analysis

Fig.7 Change of the adsorption free energy of methane and the εd on WO3-x （a）， and ELF plots of WO2.72， CH4/WO2.72 （b） and WO2， CH4/WO2 （c）

Fig.8 Gibbs free energy step diagram of the CH4 oxidation reaction on the WO3-x crystal surface

Fig.9 Charge density difference and Bader charge of methane adsorbed on the catalyst surface （the equivalent surface of CDD is 0.000 15 eV/?3， yellow and blue colors represent the electron accumulation and electron loss regions， respectively）

Fig.10 -pCOHP curves of methane adsorption by WO3-x

Fig.11 PDOS plots for methane-adsorbed WO3-x， with the Fermi level set to zero

Fig.12 AIMD curves of WO3-x

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