Defect-Driven Efficient Selective CO2 Hydrogenation with Mo-Based Clusters

Synthetic fuels produced from CO2 show promise in combating climate change. The reverse water gas shift (RWGS) reaction is the key to opening the CO2 molecule, and CO serves as a versatile intermediate for creating various hydrocarbons. Mo-based catalysts are of great interest for RWGS reactions featured for their stability and strong metal–oxygen interactions. Our study identified Mo defects as the intrinsic origin of the high activity of cluster Mo2C for CO2-selective hydrogenation. Specifically, we found that defected Mo2C clusters supported on nitrogen-doped graphene exhibited exceptional catalytic performance, attaining a reaction rate of 6.3 gCO/gcat/h at 400 °C with over 99% CO selectivity and good stability. Such a catalyst outperformed other Mo-based catalysts and noble metal-based catalysts in terms of facile dissociation of CO2, highly selective hydrogenation, and nonbarrier liberation of CO. Our study revealed that as a potential descriptor, the atomic magnetism linearly correlates to the liberation capacity of CO, and Mo defects facilitated product desorption by reducing the magnetization of the adsorption site. On the other hand, the defects were effective in neutralizing the negative charges of surface hydrogen, which is crucial for selective hydrogenation. Finally, we have successfully demonstrated that the combination of a carbon support and the carbonization process synergistically serves as a feasible strategy for creating rich Mo defects, and biochar can be a low-cost alternative option for large-scale applications.


Supporting Information
. TOF of the Mo₂C cluster supported on NGn and Nbiochar (GHSV = 930000ml/g/h, mol CO2 :mol H2 =1:2) Note: The data in above table do not reflect the peak reaction rate, as the mass transfer to catalyst surface might be limited at an ultra-high GHSV of 930000 ml/g/h, the reaction rate estimated in the article was based on test with a GHSV of 140000ml/g/h which we think would reflect the best performance of this catalyst.Table S14.Physical properties of the sample 50%Mo@NGn.
Table S15.The imaginary frequency of the transition state structures for each elementary reaction shown in Fig. 7

Fig. S5 .
Fig. S5.Fukui analysis of an intact cluster of Mo₂C supported on NGn.

Fig. S7 .
Fig. S7.Independence of CO desorption energy and Mo-CO bond strength in a variety of Mo₂C catalytic system.

Fig. S8 .
Fig. S8.(a) Electronic spin of Mo₂C_V5&10@NGn and Mo₂C_V5&10@SiO₂ before and after CO adsorption.(b) The corresponding pDOS for Mo9 and C (in CO) in the two catalytic systems.

Table S1 .
Summary of reported catalysts for RWGS reaction

Table S16 .
Reaction tests over 1%W@NGn in comparison with Mo based catalyst