In this work, we prepared ZnO, ZnAl₂O₄, and ZnAl mixed oxides with different metal molar ratios and applied them for synthesizing glycerol carbonate (GC) from glycerol and urea. The reaction routes related to the Zn species over the ZnAl mixed oxides were investigated. The ZnAl mixed oxides were found to consist of two Zn crystalline phases: ZnO and ZnAl₂O₄. From the reaction results, the ZnAl mixed oxides showed much higher glycerol conversion and GC yield than the ZnO and ZnAl₂O₄. During the reaction, the dissolution of the Zn species from the ZnO phase over the ZnAl mixed oxides was observed while the ZnAl₂O₄ phase remained insoluble. The ZnO phase provided a homogeneous reaction route via the dissolved Zn species, resulting in the formation of a Zn complex containing the isocyanate (NCO) and zinc glycerolate. In contrast, the insoluble ZnAl₂O₄ phase was responsible for not only a heterogeneous reaction route, but also adsorption of the Zn NCO complex on the catalyst. We proposed that the adsorbed Zn NCO complex could play a role as an active site for an additional heterogeneous reaction route. Therefore, the ZnAl mixed oxides exhibited high GC yields through the dual catalysis routes: the homogeneous reaction route over the ZnO phase and the heterogeneous reaction route over the ZnAl₂O₄ phase.

在这项工作中，我们制备了具有不同金属摩尔比的ZnO，ZnAl ₂ O ₄和ZnAl混合氧化物，并将其用于由甘油和尿素合成碳酸甘油酯（GC）。研究了在ZnAl混合氧化物上与Zn物种有关的反应途径。发现ZnAl混合氧化物由两个Zn结晶相组成：ZnO和ZnAl ₂ O ₄。从反应结果来看，ZnAl混合氧化物比ZnO和ZnAl ₂ O ₄具有更高的甘油转化率和GC产率。在反应过程中，观察到Zn物种从ZnO相到ZnAl混合氧化物上的溶解，而ZnAl ₂ O ₄相保持不溶。ZnO相通过溶解的Zn物种提供了均匀的反应路径，从而形成了包含异氰酸酯（NCO）和甘油酸锌的Zn络合物。相反，不溶性ZnAl ₂ O ₄相不仅负责非均相反应路线，还负责Zn NCO络合物在催化剂上的吸附。我们提出，吸附的Zn NCO络合物可以充当其他异质反应途径的活性位点。因此，ZnAl混合氧化物通过双重催化途径表现出高的GC收率：在ZnO相上方的均相反应路线和在ZnAl ₂ O ₄相上方的非均相反应路线。