Two-dimensional molybdenum carbide 2D-Mo2C as a superior catalyst for CO2 hydrogenation

Hui Zhou,Alexey Fedorov,Athanasia Tsoukalou,Evgenia Kountoupi,Pierre Florian,Zixuan Chen,Paula M. Abdala,Christoph R. Müller

doi:10.1038/s41467-021-25784-0

Abstract

Early transitional metal carbides are promising catalysts for hydrogenation of CO2. Here, a two-dimensional (2D) multilayered 2D-Mo2C material is prepared from Mo2CTx of the MXene family. Surface termination groups Tx (O, OH, and F) are reductively de-functionalized in Mo2CTx (500 °C, pure H2) avoiding the formation of a 3D carbide structure. CO2 hydrogenation studies show that the activity and product selectivity (CO, CH4, C2–C5 alkanes, methanol, and dimethyl ether) of Mo2CTx and 2D-Mo2C are controlled by the surface coverage of Tx groups that are tunable by the H2 pretreatment conditions. 2D-Mo2C contains no Tx groups and outperforms Mo2CTx, β-Mo2C, or the industrial Cu-ZnO-Al2O3 catalyst in CO2 hydrogenation (evaluated by CO weight time yield at 430 °C and 1 bar). We show that the lack of surface termination groups drives the selectivity and activity of Mo-terminated carbidic surfaces in CO2 hydrogenation.

Highlights

Transitional metal carbides are promising catalysts for hydrogenation of CO2
Earth-abundant early transitional metal carbides, and in particular carbides of Mo and W, feature catalytic properties similar to those of noble metals[1,2]. This property has been exploited for various catalytic processes including Fischer–Tropsch (FT) synthesis[3,4], methane dry reforming[5], water-gas shift (WGS) reaction[6,7], and CO/CO2 hydrogenation[8,9]
The layered structure of Mo2CTx was confirmed by X-ray diffraction (XRD) analysis (parameter c = 20.636(3) Å, Supplementary Fig. 1), consistent with the lack of a Ga signal in the X-ray photoelectron spectroscopy (XPS) spectra of Mo2CTx (Supplementary Fig. 2)[33,42]

Summary

Introduction

Transitional metal carbides are promising catalysts for hydrogenation of CO2. Here, a two-dimensional (2D) multilayered 2D-Mo2C material is prepared from Mo2CTx of the MXene family. The control experiment shows that Mo2CTx reduced using 10% H2/N2 and under otherwise identical conditions does not give 2D-Mo2C owing to the incomplete defunctionalization of Tx groups, according to XPS data (Supplementary Fig. 15 and Supplementary Table 1)[33]. XANES data reveals that 2D-Mo2C is oxidized under the WGS conditions used, reaching after 10-h of TOS an oxidation state (and a Tx surface coverage) close to that of Mo2CTx (Supplementary Fig. 33).

Results

Conclusion