d2, d3, and d4 M3C2 Transition Metal Carbides (MXenes) as Catalysts for CO2 Conversion into Hydrocarbon Fuels: A Mechanistic and Pre-dictive DFT Study

TL;DR

This study uses DFT calculations to explore d2, d3, and d4 MXenes as catalysts for converting CO2 into hydrocarbons, revealing promising materials and reaction pathways for efficient CO2 reduction.

Contribution

It provides the first detailed mechanistic and predictive DFT analysis of MXenes as CO2 conversion catalysts, highlighting promising materials and reaction steps.

Findings

Cr3C2 shows low overpotential for CO2 to CH4 conversion.

Spontaneous formation of radical species during hydrogenation.

Strong CO2 capture without water co-adsorption.

Abstract

The functioning of 2D d2, d3, and d4 transition metal carbides as CO2 conversion catalysts has been proved by well resolved density functional theory (DFT) and DFT+U theoretical calculations. Whilst MXenes from the d2 series (M = Ti, Zr, and Hf) have demonstrated active behaviors for the capture of CO2, the V3C2, Nb3C2, Cr3C2, and Mo3C2 materials exhibit the most promising results for their application in the selective CO2 conversion into CH4, with limiting reaction energies of 1.55, 1.75, 0.69, and 1.24 eV, respectively, at DFT+U computational level plus explicit DFT-D3 dispersion corrections, and specially highlighting the role of Cr3C2 due to its theoretically predicted low over potential. Moreover, important features have been predicted during the first hydrogenation step towards the formation of the OCHO and HOCO radical species, exhibiting spontaneous reaction energies in the OCHO obtaining for such promising carbides from the d3 and d4 groups. Our re-sults provide novel insights in the computer-aided searching of high performance catalysts and the understanding of reaction mech-anisms for CO2. Finally, it is hypothesized that the capture of CO2 along the early step of the reaction is spontaneously produced without pass from a physisorbed state, being the strength of such capture larger than the computed binding energies for the chemi-sorption of H2O, offering encouraging perspectives for the experimental testing of our materials in water environment