Exploring in situ functionalization strategy in a hard template process: Preparation of sodium-modified mesoporous tetragonal zirconia with superbasicity

An in situ functionalization strategy was developed in a hard template process to fabricate mesoporous solid superbases, and sodium-modified mesoporous zirconia (NaMZ) was successfully prepared. The obtained materials were characterized by various methods including XRD, TEM, N₂ adsorption, IR spectroscopy, XRF, and CO₂ TPD. The results show that the NaMZ materials exhibit well-defined mesostructure, tetragonal crystalline frameworks, and superbasicity with a high strength of 27.0. The NaOH solution plays a double role by removing the silica template SBA-15 and functioning as the guest. The sodium species is thus coated onto the mesoporous zirconia formed in situ. Hence, the fabrication and functionalization of mesoporous zirconia can be realized in one step, which avoids the possible structural damage of nonsiliceous mesoporous oxides in post-treatment. The stability of metastable tetragonal zirconia was found to be due to the confined space provided by the mesoporous silica template and the formation of Si-O-Zr linkages. It was also demonstrated that the NaMZ materials exhibited excellent basic catalytic performance. The turnover frequency (TOF) value on the material NaMZ-2 can reach 95.0 h^-1 with 100% selectivity to the target product dimethyl carbonate, which is much higher than the value for the extensively used homogeneous catalyst CH₃ONa (45.8 h^-1).