Two-dimensional graphene-like materials, namely MXenes, have been proposed as potential materials for various applications. In this work, the reactivity and selectivity of four MXenes (i.e. MC (M = Ti, V, Nb, Mo)) and their oxygen-functionalized forms (i.e. O-MXenes or MCO) toward gas molecules were investigated by using the plane wave-based Density Functional Theory (DFT) calculations. Small gas molecules, which are commonly found in flue gas streams, are considered herein. Our results demonstrated that MXenes are very reactive. Chemisorption is a predominant process for gas adsorption on MXenes. Simultaneously dissociative adsorption can be observed in most cases. The high reactivity of their non-functionalized surface is attractive for catalytic applications. In contrast, their reactivity is reduced, but the selectivity is improved upon oxygen functionalization. MoCO and VCO present good selectivity toward NO molecules, while NbCO and TiCO show good selectivity toward NH. The electronic charge properties explain the nature of the substrates and also interactions between them and the adsorbed gases. Our results indicated that O-MXenes are potential materials for gas-separation/capture, -storage, -sensing, etc. Furthermore, their structural stability and SO-tolerant nature are attractive properties for using them in a wide range of applications. Our finding provides good information to narrow down the choices of materials to be tested in future experimental work.

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NO on anatase-TiO2 (001) was mainly in the form of NO2 which could trigger the subsequent ‘fast SCR’ reaction.

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Here, propane dehydrogenation (PDH) to propylene and side reactions, namely, cracking and deep dehydrogenation on Ni(111) surface, have been theoretically investigated by density functional theory calculation. On the basis of adsorption energies, propane is physisorbed on Ni(111) surface, whereas propylene exhibits chemisorption supported by electronic charge results. In the PDH reaction, possible pathways can occur via two possible intermediates, i.e., 1-propyl and 2-propyl. Our results suggest that PDH reaction through 1-propyl intermediate is both kinetically and thermodynamically more favorable than another pathway. The C–C bond cracking during PDH process is more difficult to occur than the C–H activation reaction because of higher energy barrier of the C–C bond cracking. However, deep dehydrogenation is the preferable process after PDH, owing to the strong adsorption of propylene on Ni(111) surface, resulting in low selectivity of propylene production. This work suggests that Ni(111) has superior activity toward PDH; however, the enhancement of propylene desorption is required to improve its selectivity. The understanding in molecular level from this work is useful for designing and developing better Ni-based catalysts in terms of activity and selectivity for propane conversion to propylene.

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Active Lewis acid sites in γ-Al2O3 promote the catalytic activity for lactic acid production from d-xylose.

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