Effect of Cu incorporation strategy and Ce modification of UiO-66 on propylene carbonate formation via 1,2-propanediol carboxylation

Introduction. The increasing concentration of atmospheric CO₂ has stimulated the development of technologies for its capture and utilization. Among the possible valorization routes, the synthesis of cyclic organic carbonates from CO₂ is particularly attractive due to their broad industrial applications in polymer production and lithium-ion battery electrolytes. Metal-organic frameworks (MOFs) have emerged as promising catalysts for CO₂ conversion because of their high surface area, tunable porosity, and accessible active sites. In this work, zirconium-based UiO-66 was modified with cerium and copper species to enhance its catalytic performance in the carboxylation of propylene glycol to propylene carbonate.

Methods. A series of UiO-66(Zr)-based catalysts, with and without cerium modification, were prepared by introducing copper species through impregnation or encapsulation methods. The obtained materials were characterized using X-ray diffraction, nitrogen sorption, infrared spectroscopy and X-ray photoelectron spectroscopy to determine their crystallographic, textural, and morphological properties. Catalytic activity was evaluated in carboxylation of propylene glycol with CO₂ under T=130°C, p=60 bar, t=7 h and in the presence of dehydrating agents (acetonitrile and benzonitrile). The catalysts were additionally characterized after reaction to assess their structural stability.

Results. The introduction of cerium and copper species enhanced the catalytic activity toward propylene carbonate formation, with product concentrations ranging from 2 to 30 mg/mL depending on the catalyst composition and preparation method. The incorporation of cerium and/or copper species was achieved without significant deterioration of the UiO-66 framework. Most of catalysts retained their crystallinity and textural properties after metal modification and catalytic testing, indicating excellent stability under the applied reaction conditions.

Conclusions. Copper and cerium modified UiO-66(Zr) materials exhibit high structural stability and promising catalytic activity in the conversion of CO₂ with propylene glycol. These findings demonstrate the potential of metal-modified UiO-66 catalysts for the sustainable production of value-added cyclic carbonates from carbon dioxide.