MXenes are commonly synthesized through selective etching of the corresponding MAX phase, which has the formula M-A-X, where "M" is the early transition metal, "A" is a main group metal, and "X" is carbon or nitrogen. Over the past decade, they have gained attention for their applications, particularly as electrocatalysts, becoming one of the most active materials in this field【4】

The research concept to be presented explores the potential of MXenes as highly efficient and stable thermal catalysts for organic reactions. The active sites in MXenes include M–O and M–OH groups, which are analogous to those found on the surfaces of transition metal oxides. Additionally, MXenes feature unique surface terminations resembling those in molecular complexes, further broadening their catalytic versatility.

Results and Discussion

The presentation will highlight the potential of MXenes as materials with intrinsic catalytic activity for a wide range of organic reactions. These include aerobic oxidations, oxidative dehydrogenation of hydrocarbons and other functional groups, hydrogenation of unsaturated C-C multiple bonds, aldol condensations, hydroamination of C≡C triple bonds, guanylation of amines, among others. The study focuses on a series of MXenes, including Ti₃C₂, Nb₂C, and V₂C, synthesized from commercially available MAX phase precursors.

The characterization of Brønsted and Lewis acid/base sites using NH₃-TPD, CO₂-TPD, and pyridine adsorption/desorption monitored by IR spectroscopy reveals a low density of active sites. These sites are likely associated with structural defects, atomic vacancies, and surface terminations introduced during the harsh etching process. Despite their low abundance, these defects are primarily responsible for the observed catalytic activity. Additionally, the morphology of the MXene samples—whether multilayered accordion-like, expanded layered, or exfoliated—significantly influences catalytic performance. Post-synthesis surface functionalization further modifies catalytic activity, with certain modifications positioning MXenes among the most active solid catalysts in terms of turnover frequency.

Beyond their intrinsic catalytic properties, MXenes are particularly effective as supports for single-atom catalysis. Single atoms can be incorporated into MXenes directly during their synthesis via the molten salt method. These single atoms occupy vacant sites in the metal layer, enabling catalytic activity in specific reactions, such as hydrogenations. This dual functionality—intrinsic activity and support for single-atom catalysis—illustrates the versatility and potential of MXenes in advanced catalytic applications.

Significance

The catalytic activity of metal oxides, carbides, and related compounds is well established. In this context, MXenes offer distinct advantages as catalysts due to their unique 2D morphology, which provides highly accessible active sites and improved atom utilization. The tunable chemical composition of MXenes opens up an expansive chemical space, with over 70 materials reported to date. Moreover, their catalytic activity can be further optimized through precise control of surface termination groups, enhancing their performance. These features make MXenes highly promising catalysts for a wide range of organic reactions, combining structural efficiency with chemical versatility.