Promoting CO₂ conversion to dimethyl carbonate with N- and S-assisted defect-modulated CeO₂ nanomaterials

Direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol is thermodynamically challenging and requires catalysts with finely tuned surface properties. In this work, we present the design and synthesis of a series of nitrogen- and sulfur-assisted, defect-modulated ceria nanorods (N_XCeO₂-NR and S_XCeO₂-NR) to tailor oxygen vacancy density, Ce³⁺ concentration, surface acidity, and basicity, to assess their catalytic performance in DMC synthesis. The nanomaterials were comprehensively characterized by Raman spectroscopy, powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), Brunauer–Emmett–Teller (BET) surface analysis, and temperature-programmed desorption (TPD) of CO₂ and NH₃. Compared to pristine nanorod CeO₂ (CeO₂-NR) and nanopolyhedron CeO₂ (CeO₂-NP), the defect-modulated materials displayed markedly enhanced catalytic activity. Specifically, N₆CeO₂-NR and S₆CeO₂-NR achieved the highest DMC productivity of 66.4 and 63.3 mmol g_cat⁻¹h⁻¹, respectively, with nearly 100% selectivity under moderate reaction conditions in the presence of a dehydrating reagent 2-cyanopyridine (2-CP). The remarkable performance of N₆CeO₂-NR and S₆CeO₂-NR can be attributed to their significantly improved surface properties, including balanced acidity, basicity, elevated Ce³⁺ ion concentration, and increased oxygen vacancy density. These enhancements, which distinguish them from the pristine CeO₂, were confirmed through detailed analyses using TPD, XPS, and Raman spectroscopy. These findings highlight N- and S-assisted defect-engineered CeO₂ nanomaterials as a promising class of catalysts for DMC synthesis.