Direct Colloidal Synthesis of High-Entropy Carbide Nanoparticles with Altered CO2 Hydrogenation Selectivity

The controlled synthesis of refractory carbide nanoparticles remains a longstanding challenge in colloidal nanoscience because strong metal–carbon bonding and high formation energies complicate nucleation, growth, and compositional control. Here, we report the direct colloidal synthesis of single-phase high-entropy (HE) carbide nanoparticles, (CrMnMoW)C1–x, (TiCrMnMoW)C1–x, and (CrMnFeMoW)C1–x, via the simultaneous thermolysis of transition metal carbonyl precursors in oleylamine. Structural analysis reveals substantial local disorder and lattice distortion, including a ∼50% increase in the full width at half-maximum of the first M–C pair distribution function peak relative to α-MoC1–x nanoparticles. During CO2 hydrogenation (at 300 °C and either 20 or 30 bar), the HE carbides exhibit lower CO selectivity than the monometallic α-MoC1–x control, decreasing from 77% to 38–67%, while shifting selectivity toward oxygenates and C2+ products. The largest enhancement in methanol and dimethyl ether formation was observed for (TiCrMnMoW)C1–x, increasing from 0.5% for the control to 6.7%, while (CrMnFeMoW)C1–x exhibited a 50% increase in C2+ selectivity, from 6.8% to 10.2%. These findings demonstrate that direct colloidal access to HE carbide nanoparticles provides a route to catalytic behavior distinct from that of conventional carbide nanoparticles.