Metal-organic framework/polyurea composite microreactors prepared in oil-in-oil emulsions

A new technique was developed to create composite microcapsules consisting of metal–organic framework (MOF) and polyurea. This method employs oil-in-oil (O/O) emulsion as a template for forming these microcapsules. It involves emulsifying a polar solvent containing MOF reagents within a nonpolar phase containing a suitable surfactant and an isocyanate monomer. Subsequently, the addition of the amine monomer initiates two simultaneous processes: the formation of MOF crystals in the core of polar droplets and the interfacial polymerization to create polyurea shell. Optimization of the method involved adjusting various parameters affecting the composite microcapsules' structure and morphology. These parameters include the surfactant's type and concentration, the emulsion phases’ type and concentration, and quantity of the MOF component. This method was applied to create palladium-based MOF/polyurea microreactors by encapsulating sodium tetrachloropalladate and then reducing the palladium salt with hydrogen to generate reactive palladium species. The produced catalysts were utilized in the selective hydrogenation of terminal alkynes. It was observed that the selectivity of the catalyst is influenced by the quantity of encapsulated MOF, the amount of encapsulated palladium, and the solvent type used for the reaction.