Carbon Nanotube-Supported Mo, Ni, and Co Nitrides as Stable Catalysts for Levulinic Acid Conversion: Influence of Metal-Nitrogen Interactions and Confinement Effects.

Abstract

Transition metal nitrides (MxNy, where M = Mo, Ni, or Co) supported on carbon nanotubes (CNTs) are synthesized and evaluated as catalysts for the conversion of levulinic acid at 250 °C and 50 bar H₂. The catalysts are extensively characterized by N₂ physisorption, XRD, TEM, FT-IR, H₂-TPR, NH₃-TPD, 2-propanol conversion, and XPS. Among the series, the Mo₂N/CNT catalyst exhibits stronger metal-support interaction, smaller particle size, and more pronounced confinement within the CNT structure. This is attributed to the higher Mo-N bond strength compared to Ni-N and Co-N, which also influence the density and strength of surface acid sites. In contrast, the Ni₃N/CNT catalyst displays the highest catalytic activity and is associated with smaller nitride particles located on the external CNT surface. The Co₄N/CNT catalyst shows intermediate behavior. Product selectivity is primarily governed by the presence of surface nitride and oxynitride species, rather than the specific nature of the transition metal. These findings highlight the role of metal-support interactions and active phase dispersion in the design of stable, nonnoble metal catalysts for biomass-derived platform molecule conversions.