Controlled Grafting Synthesis of Silica-Supported Boron for Oxidative Dehydrogenation Catalysis

We present the controlled grafting synthesis of pinacolborane on amorphous silica. 11B solid-state NMR and IR spectroscopies reveal that the precursor molecule anchors monopodally to the surface and can form hydrogen-bonding interactions with neighboring unreacted silanol groups. The extent of hydrogen bonding can be controlled by the silica pretreatment dehydration temperature. Thermal treatment of the grafted boron materials under vacuum generates clusters of oxidized/hydrolyzed boron regardless of boron weight loading, illustrating that boron is highly mobile on the silica surface at elevated temperatures. The materials exhibit propane oxidative dehydrogenation activity expected for silica-supported boron catalysts. Interestingly, the kinetic behavior of these supported catalysts deviates from that of previously reported bulk boron materials, prompting further studies into the reaction kinetics over these materials. The synthetic and catalytic insights gained here can inform future studies of improved synthesis routes and reaction kinetics.