Heteroatom-assisted oxygen vacancies in cerium oxide catalysts for efficient synthesis of dimethyl carbonate from CO2 and methanol

The direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol is a green synthetic route owing to the nontoxicity of starting materials and synthetic protocol. One of the key challenges in this approach resides in designing effective catalysts which could activate CO2 and methanol efficiently leading to a high yield of DMC. In this aspect, heteroatom (N and S) assisted CeO2 nanorod materials (S-CeO2-NR and N-CeO2-NR) and pristine CeO2-NR were synthesized to modulate the surface oxygen vacancies, Ce3+ concentration, acidity and basicity. The nanomaterials were characterized thoroughly by the combination of spectroscopic (Raman, powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS)), microscopic (high-resolution transmission electron microscopy (HR-TEM)) and surface analytical techniques (N-2-physisorption, CO2- and NH3-temperature programmed desorption (TPD)). Among the CeO2 nanomaterials including commercial CeO2-NP, the N-CeO2-NR outperformed all, exhibiting the highest yield of DMC under moderate reaction conditions in the order of N-CeO2-NR (113.3 mmol g(cat)(-1)) > S-CeO2-NR (49.7 mmol g(cat)(-1)) > CeO2-NR (28.8 mmol g(cat)(-1)) > CeO2-NP (0.8 mmol g(cat)(-1)) with 100% DMC selectivity. The enhanced efficiency of heteroatom-assisted materials (N-CeO2-NR and S-CeO2-NR) can be ascribed to their superior surface acidity, basicity, Ce3+ concentration, and oxygen vacancy concentrations in comparison to analogous materials, as supported by TPD, XPS and Raman analysis respectively.