(509t) Synthesis of Symmetrical Urea Derivatives from CO2 and Amines over Copper-Based Core-Shell Catalysts

Urea derivatives are key intermediates in the synthesis of agrochemicals and pharmaceuticals, and also have applications as additives in fuels and polymers. Traditional production routes require the use of highly toxic chemicals such as phosgene, isocyanates and carbon monoxide. Carbon dioxide is emerging as an alternative feedstock for the production of urea derivatives, avoiding the use of such hazardous materials. The use of CO₂, however, requires catalysts based on rare and expensive metals and long reaction times of up to 48 h. The present work shows the successful development of catalyst materials based on cheap and abundant copper, with reduced reaction times.

Urea derivatives synthesis was conducted using 20 mmol butylamine, 30 bar CO₂, 4 ml organic solvent and 10 mol% catalyst at 423 K in an autoclave with a volume of 40 ml. The influence of solvent, reaction time and different metal oxide catalysts on reaction yield were studied to optimise reaction conditions.

Results demonstrate that supported CuO can successfully catalyse the synthesis of urea derivatives from CO₂ with a reaction yield up to 50% at 423 K in 5 h. While effective catalysts, these materials suffer from leaching of the active metal oxide during reaction due to the presence of ammonia in solution. This limits the recyclability of the catalyst. In order to address this while maintaining the benefits of the copper oxide catalyst, core-shell catalysts have been prepared. In these materials the active phase is encapsulated by an inert outer shell, thereby avoiding catalyst deactivation because of migration, sintering or leaching. Two different core-shell catalysts, CuO@SiO₂, have been prepared via hydrothermal synthesis from biomass and sol-gel synthesis, respectively. TEM, SEM, BET, XRD, and FTIR and Raman spectroscopies have been used to characterise the catalysts and relate catalytic performance to catalyst structure.