(628c) Preparation and Characterization of Mesoporous Silica Supported Gold Catalysts for Selective Oxidations

Reversible ionic liquid (RevIL) is a class of ionic liquids capable of transitioning between molecular and ionic forms in response to two stimuli. Upon the removal of CO₂ via gentle heating, RevIL reverses into its molecular form and detaches from the gold surface. Herein, we demonstrate the use of RevIL to synthesize and deposit well-defined gold nanoparticles inside the mesopores of SBA-15 silica without chemical modifications of the silica surface as required in traditional methods. The location of gold nanoparticles inside the mesopores is confirmed by microscopic images and improved nanoparticle thermal stability. The prepared porous gold catalysts are extremely active and selective in the selective oxidation of benzyl alcohol without calcination due to the bare gold surface. Importantly, the porous gold catalysts show up to a 50% increase in surface turnover frequency compared to the nonporous gold catalysts also prepared with RevIL, implying improved catalytic activity. By controlling the geometry of gold catalysts, we alter the pore environment near the gold surface to tune the reagent’s (benzyl alcohol molecules’) mass transport, impacting catalytic activity. In the following studies, we investigated the reagent’s movement (translational and rotational) near the gold surface via NMR techniques and constructed a computational model to investigate the reagent’s adsorption process within the mesopores. We found that the mesopores do not induce translational mass transport limitation but hinders the random rotation of reagent. In addition, the pore structure optimizes the adsorption behavior of the reagent by promoting the alignment of benzyl alcohol’s hydroxyl group with the gold surface meanwhile inhibiting the adsorption of benzyl alcohol’ phenyl ring that blocks active sites. This inhibition reduces the likelihood of active site blockage and its interference with catalytic activity.