Ga-MCM-41 nanoparticles: Synthesis and application of versatile heterogeneous catalysts

Ga-MCM-41 materials with nanosized particles (<150 nm) were prepared according to two new synthesis methods. The structural and textural properties of the materials were characterized by XRD, N₂-physisorption, TEM, SEM and EDX, while ⁷¹Ga MAS-NMR was employed to monitor the coordination of the gallium atoms. The two materials were tested as heterogeneous catalysts in three relevant reactions in the context of green production of valuable chemicals: (1) the reaction of glycerol with acetone to produce solketal; (2) the conversion of the triose sugar dihydroxyacetone to ethyl lactate; (3) the epoxidation of cyclooctene with aqueous hydrogen peroxide. The two nanosized Ga-MCM-41 materials show different catalytic behaviour in the various reactions, with the material prepared with lower Si/Ga displaying a higher versatility. This catalyst reaches higher turnover numbers compared to conventional Ga-MCM-41 reported in the literature. This result is ascribed to the higher specific surface area and to the shorter channels of the nanoparticles, which enhance the accessibility of the active sites.