Zn-Zr-Al oxides derived from hydrotalcite precursors for ethanol conversion to diethyl carbonate

Ethanol conversion to high-value-added products has attracted considerable attention in both academic research and industrial fields. In this study, we synthesized a series of tunable acid–base bifunctional Zn-Zr-Al metal oxides (represented as Zn₂Zr_xAl-MMO) in light of the structural topotactic transformation of Zn₂Zr_xAl-hydrotalcite precursors (Zn₂Zr_xAl-LDH). The resulting Zn₂Zr_xAl-MMO catalysts were employed in the conversion of ethanol to diethyl carbonate. The Zr⁴⁺ ion content of the LDH precursor plays a key role in modulating the acid-base properties and determining catalytic performance: the Zn₂Zr_0.1Al-MMO sample exhibits the optimal catalytic behavior with a diethyl carbonate (DEC) yield of 42.1%, which is the highest reported for metal oxide catalysts. Structure-property correlation investigations revealed that the synergic catalysis between medium-strong basic sites and weak acid sites plays a predominant role in the catalytic behavior. Furthermore, in situ Fourier transform infrared measurements showed that the weak acidic site promotes activation adsorption of the reactant (urea) and the intermediate product (ethyl carbamate), while the medium-strong basic site accelerates ethanol activation. Moreover, the Zn₂Zr_0.1Al-MMO catalyst has the advantages of cost effectiveness, good stability, and reusability. Therefore, the acid-base bifunctional catalysts developed in this work can be employed as promising candidates in acid-base catalytic reactions such as ethanol conversion.