Activation of the CO2 molecule on Mxenes Nitrides

2018 edition

Raul Morales Salvador

Nowadays, 85% of total world demanded energy is supplied by thermal power plants fed by fossil fuels including coal, oil and gas. The use of these materia as a source of energy and other activities for the development of the humanity, as non-suitable farming, transportation of commodities, and directly consume by the users for the daily life emit high quantities of exhaust gases.  The emission of exhaust gases into the atmosphere, mainly carbon dioxide (CO2), is regarded as a major cause of the global warming, climate change and ocean acidification through the so-called greenhouse effect. Therefore, the depletion of CO2 emissions is one of the main challenges of our society. To face this subject, different ways have been proposed such as alternative energy sources or reduce the emission of CO2 by the industry.

Alternatively, a promising way to reduce the concentration of CO2 in the atmosphere is based on efficient technologies for Carbon Capture and the subsequent Storage(CCS). This solution is specially appealing so use CO2 as a chemical feedstock to manufacture saleable products, with concomitant impacts in industry and economy, making it an efficient path to face the climate change. CCS protocol requires materials capable of capturing and activing CO2 for its conversion into other chemical products.

MXenes (carbides and nitrides) could be feasible for the CO2 activation. These novel materials have been recently obtained. MXenes (Mn+1Xn)  family includes different stoichiometries (n = 1-3) and single MXene sheets can be formed by 3, 5, or 7 atomic layers which correspond to M2X, M3X2, and M4X3, respectively, and so, can be regarded as essentially 2D materials. Density functional theory (DFT) have predicted more than 25 different ordered MXene materials, they are nitrides, carbonitrides and carbides.

The target of study is the MxN nitrides using for for M= Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W. The stoichiometry is M2N. The slabs of the materials theoretically studied are composed by 3 layers forming a Sandwich: the top and the bottom layer contains 9 atoms of the chosen metal, each one; the layer between the metals layers contains 9 atoms of Nitrogen.

The stability of these materials, the strength of the formed bond by the adsorbed molecule and the surface, the deformation of molecule and its consequently activation, the adsorption and desorption rates and the storage capacity are studied in order to valorate these materials as a possibility to face the climate change.