MXenes are recently discovered 2D carbides, nitrides, or carbonitrides [1]. Depending on their composition, they exhibit intrinsic catalytic properties or can be synergistically promoted with metal nanoparticles or single atoms. Unlike for electro- and photocatalysis, thermal catalysis on MXenes has been little investigated so far. Herein, through a systematic study of Ti3C2Tx (“MX”) and Mo2Ti2C3Tx (“MoMX”) MXenes, as-prepared or loaded with ultradispersed metals, trends connecting the MXene surface state, metal resistance to sintering, and catalytic properties in CO2 hydrogenation are established. Ti3C2Tx and Mo2Ti2C3Tx were obtained from the respective Ti3AlC2 and Mo2Ti2AlC3 MAX phases by LiF/HCl and HF etching, respectively [2]. After their delamination in water (plus an intercalation step in TBAOH for Mo2Ti2C3Tx), Pt, Pd, Cu and Co were deposited onto the MXenes by incipient wetness impregnation. The samples were then drop casted on silica to avoid restacking, pretreated under H2 flow up to 450 °C, and evaluated in a flow-fixed bed reactor at a total reactant pressure of 30 bar (H2:CO2 = 3:1). Pre- and post-reaction characterizations involved XRD, XPS, TGA, SEM, and STEM techniques. Results and discussion. Unlike Ti3C2Tx, bare Mo2Ti2C3Tx reveals a high activity for the reverse water-gas shift reaction in the 250-350 °C range. Furthermore, for both systems, Pt addition at low loading (<1 wt%) enhances the activity and the CO selectivity. In contrast, Pd, Cu and Co negligibly affect the performance of Mo2Ti2C3Tx. Together with the metal identity controlling the H2 activation rate, the superior promoting effect of Pt is ascribed to the greater propensity of this metal to atomically and stably anchor at the MXene surface. [1] VahidMohammadi, A.; Rosen, J.; Gogotsi, Y. Science 2021, 372, 1165. [2] Benchakar, M. et al. Appl. Surf. Sci. 2020, 530, 147209.