Conversion of carbon dioxide (CO₂) to C1 products such as carbon monoxide (CO) is a critical step towards carbon valorization. The conversion has been largely carried out through the reverse water gas shift (RWGS) reaction using noble metal catalysts or copper-based nanostructures. Similarities in the electronic structures between beta phase molybdenum carbides (β-Mo₂C) and platinum-group metals make them promising alternatives to traditional catalysts. In this work, we studied the effect of oxide supports (MO_x, M = Al, Ce, Mg, Si, and Ti) on the formation and catalytic properties of β-Mo₂C nanoparticle catalysts. The β-Mo₂C/SiO₂ catalyst exhibited a mass activity of 372 μmol_CO2∙ ${\mathrm{g}}_{\mathrm{M}{\mathrm{o}}_2\mathrm{C}}^{-1}$∙s⁻¹ at 400 °C and 1109 μmol_CO2∙ ${\mathrm{g}}_{\mathrm{M}{\mathrm{o}}_2\mathrm{C}}^{-1}$∙s⁻¹ at 600 °C for the conversion of CO₂. The β-Mo₂C/SiO₂ catalysts also maintained selectivity and showed structural stability in the on-stream study. The enhanced catalytic performance could be attributed to the size of nanocatalysts (4.7 nm), whereas the stability is related to the interaction with SiO₂ and the low H₂:CO₂ feed ratio. This work highlights the application of amorphous silica in preparing metal carbide nanocatalysts. The rich defects and surface vacancies in the silica support greatly facilitate the high-rate and highly selective processes towards the valorization of CO₂.

Unlike nucleation and growth in simple precipitation processes, described by the classical theory, metal nanoparticles formed in organic solvents with capping ligands often involve chemical reactions that occur homogeneously in solution or heterogeneously on the metal surface. These chemical reactions lead to the formation of intermediates that occurs in the process of deposition onto nuclei during the reduction. The understanding of these chemical reactions would enable a better design of functional metal nanocrystals, even those with unconventional hierarchical morphologies. In this study, we report the formation of dish-shaped nanostructures of palladium (Pd) obtained from palladium acetylacetonate (Pd(acac)₂) in the presence of oleylamine and oleic acid. The process was correlated with the kinetic-controlled evolution of two-dimensional (2D) Pd nanosheets. The formation of Pd-ligand complexes was revealed using single-crystal X-ray diffraction, ultraviolet-visible spectroscopy, and mass spectrometry. These intermediates affected the formation kinetics of the 2D nanostructures and higher-ordered morphology of the nanodishes.