The interaction of CO 2 with nitride MXenes of different thickness is investigated using periodic density functional theorybased calculations and kinetic simulations carried out in the framework of transition state theory, the ultimate goal being predicting their possible use in Carbon Capture and Storage (CCS). We consider the basal (0001) surface plane of nitride MXenes with M n + 1 N n (n = 1-3; M=Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) stoichiometry and also compare to equivalent results for extended (001) and ( 111) surfaces of the bulk rock-salt transition metal nitride compounds. The present results show that the composition of MXenes has a marked influence on the CO 2 -philicity of these substrates, whereas the thickness effect is, in general, small, but not negligible. The largest exothermic activation is predicted for Ti-, Hf-, and Zr-derived MXenes, making them feasible substrates for CO 2 trapping. From an applied point of view, Cr-, Mo-, and W-derived MXenes are especially well suited for CCS as the interaction with CO 2 is strong enough but molecular dissociation is not favored. Newly developed kinetic phase diagrams are introduced supporting that Cr-, Mo-, and W-derived MXenes are appropriate CCS substrates as they are predicted to exhibit easy capture at mild conditions and easy release by heating below 500 K.

A density functional theory study is presented addressing the surface energy stabilization mechanisms of transition metal carbide and nitride surfaces of a crystal structure different from that of the most...

A density functional theory study is presented here aimed at investigating whether the atomic stacking on the new family of two-dimensional MXene materials has an influence on their adsorption properties and whether these properties can provide information about this structural feature. To this end, the Mo 2 C MXene, exhibiting two nearly degenerate crystal structures with either ABC or ABA atomic stacking, is chosen as a case study. The study of the adsorption of CO, CO 2 , and H 2 O on both polymorphs of Mo 2 C reveals substantial differences that could be used in experiments to provide information about the atomic stacking of a given sample. Particularly, we show that the asymmetric and symmetric stretching modes of the adsorbed CO 2 and the CO stretching mode are clear features that allow one to identify the stacking of atomic layers of the Mo 2 C MXene. The present finding is likely to apply to other MXenes as well.

The potential of the Mo2C MXene to catalyze the reverse water gas shift (RWGS) reaction has been investigated by a combination of density functional theory (DFT)-based calculations, atomistic thermodynamics, and microkinetic simulations. Different catalytic routes are explored including redox and associative (carboxyl and formate) mechanisms at a high temperature at which the RWGS reaction is exothermic. The present study predicts that, on the Mo2C MXene, the RWGS reaction proceeds preferentially through the redox and formate catalytic routes, the rate-limiting step being the formation of the OH intermediate followed by the H2O formation, whereas the carboxyl route to form the carboxyl intermediate is hindered by a large energy barrier. Microkinetic simulations confirm the formation of carbon monoxide (CO) under relatively mild conditions (i.e., ∼400 °C and 1 bar). The CO formation is not affected either by the total pressure or by the CO2/H2 ratio. However, water formation requires high temperatures of ∼700 °C and pressures above 5 bar. In addition, an excess of hydrogen in the CO2/H2 ratio favors water formation. Shortly, the present study confirms that the Mo2C MXene emerges as a heterogeneous catalyst candidate for generating a CO feedstock that can be used for subsequent transformation into methanol through the Fischer–Tropsch process.