abstract
The rate-limiting step for ammonia (NH3) production via the Haber-Bosch process is the dissociation of molecular nitrogen (N-2), which requires quite harsh working conditions, even when using appropriate heterogeneous catalysts. Here, motivated by the demonstrated enhanced chemical activity of MXenes- a class of two-dimensional inorganic materials- toward the adsorption of quite stable molecules such as CO2 and H2O, we use density functional theory including dispersion, to investigate the suitability of such MXene materials to catalyze N-2 dissociation. Results show that MXenes exothermically adsorb N-2 with rather large adsorption energies ranging from -1.11 to -3.45 eV and elongation of the N-2 bond length by similar to 20%, greatly facilitating their dissociation with energy barriers below 1 eV, reaching 0.28 eV in the most favorable studied case of W2N. Microkinetic simulations indicate that the first hydrogenation of adsorbed atomic nitrogen is feasible at low pressures and moderate temperatures, and that the production of NH3 may occur above 800 K on most studied MXenes, in particular, in W2N. These results reinforce the promising capabilities of MXenes to dissociate nitrogen and suggest combining them co-catalytically with Ru nanoparticles to further improve the efficiency of ammonia synthesis.
keywords
GAS SHIFT REACTION; AMMONIA-SYNTHESIS; CARBIDE MXENE; SURFACE; IRON; MICROKINETICS; SIMULATIONS; ADSORPTION; STABILITY
subject category
Chemistry
authors
Gouveia, JD; Morales-Garcia, A; Vines, F; Gomes, JRB; Illas, F
our authors
José Daniel Lago da Silva Neves Gouveia
Assistant Researcher
José R. B. Gomes
Principal Researcheracknowledgements
The research carried out at the CICECO-University of Aveiro Institute of Materials was developed within the scope of projects UIDB/50011/2020 and UIDP/50011/2020, financed by the Portuguese Fundacao para a Ciencia e a Tecnologia (FCT/MCTES), and co-financed by the European Regional Development Fund (FEDER) under the PT2020 Partnership Agreement. The research carried out at the Universitat de Barcelona has been supported by the Spanish MICIUN/FEDER RTI2018-095460-B-I00 and Maria de Maeztu MDM-2017-0767 grants and, in part, by Generalitat de Catalunya 2017SGR13 grant. J.D.G. is also thankful to projects CENTRO-01-0145-FEDER-31002 (SILVIA) and HPC-EUROPA3 (INFRAIA-2016-1-730897) supported by the EC Research Innovation Action under the H2020 Programme. A.M.-G. thanks Spanish MICIUN for his Juan de la Cierva (IJCI-2017-31979) postdoctoral grant, F.V. is thankful to Ministerio de Economia y Competitividad (MEC) for his Ramon y Cajal (RYC-2012-10129) research contract, and F.I. acknowledges additional support from the 2015 ICREA Academia Award for Excellence in University Research.