Ordered versus Non-Ordered Mesoporous CeO₂-Based Systems for the Direct Synthesis of Dimethyl Carbonate from CO₂

In this work, non-ordered and ordered CeO₂-based catalysts are proposed for CO₂ conversion to dimethyl carbonate (DMC). Particularly, non-ordered mesoporous CeO₂, consisting of small nanoparticles of about 8 nm, is compared with two highly porous (635-722 m²/g) ordered CeO₂@SBA-15 nanocomposites obtained by two different impregnation strategies (a two-solvent impregnation method (TS) and a self-combustion (SC) method), with a final CeO₂ loading of 10 wt%. Rietveld analyses on XRD data combined with TEM imaging evidence the influence of the impregnation strategy on the dispersion of the active phase as follows: nanoparticles of 8 nm for the TS composite vs. 3 nm for the SC composite. The catalytic results show comparable activities for the mesoporous ceria and the CeO₂@SBA-15_SC nanocomposite, while a lower DMC yield is found for the CeO₂@SBA-15_TS nanocomposite. This finding can presumably be ascribed to a partial obstruction of the pores by the CeO₂ nanoparticles in the case of the TS composite, leading to a reduced accessibility of the active phase. On the other hand, in the case of the SC composite, where the CeO₂ particle size is much lower than the pore size, there is an improved accessibility of the active phase to the molecules of the reactants.