Enhanced Lewis basicity of ZIF-8 from metal incorporation (Mg, Cu, or Ce) for glycerol carboxylation using CO2 as a feedstock

Herein, Mg, Ce, and Cu were incorporated into ZIF-8 to improve its Lewis basicity for glycerol carbox-ylation. Upon metal incorporation, the Ce-and Cu-incorporated ZIF-8 remained structurally intact with slightly increased Lewis basicity, whereas the Mg-incorporated ZIF-8 exhibited a more perturbed structure containing additional exposed N atoms and metal sites (Zn and Mg). The improved Lewis basicity facilitated the increased glycerol conversion of the Mg-incorporated ZIF-8 and its yield of glycerol carbonate in the presence of CH3CN as a homogeneous dehydrating agent. Using NaHCO3 as the heterogeneous dehydrating agent, a much higher selectivity (90%) was obtained over Mg-incorporated ZIF-8 compared to that of CH3CN (similar to 60% higher), attributed to a high water sorption capability of NaHCO3 that inhibits side reactions. The heterogeneity of NaHCO3 enables efficient recycling (>3 cycles) for repeated catalytic glycerol carboxylation. The results suggested that metal incorporation is an effective and facile approach to improve ZIF-8 Lewis basicity, combined with heterogeneous NaHCO3 as the dehydrating agent, which is beneficial for glycerol carboxylation using CO2 as a feedstock. (C) 2023 Elsevier Ltd. All rights reserved.