(296e) Slowing the Kinetics of Alumina Sol-Gel Chemistry for Controlled Catalyst Overcoating and Improved Catalyst Stability and Selectivity

Catalyst
overcoating is an emerging approach to engineer controlled surface
functionalities on supported metal catalyst and improve catalyst selectivity
and durability. Alumina deposition on high surface area material by sol-gel
chemistry has traditionally been difficult to control due to the fast
hydrolysis kinetics of aluminum-alkoxide precursors.
Here, we adapt sol-gel chemistry methods to slow down these
kinetics. Specifically, we report two novel liquid phase sol-gel methods
to deposit nanometer-scale alumina overlayer with similar chemical properties
but distinct physical textures, onto high surface area substrates. The alumina
overcoats are comparable in conformality to the overcoats prepared from atomic
layer deposition. Our strategy relies on regulating the hydrolysis/condensation
kinetics of Al(^sBuO)₃ by adding a chelating agent or
using non-hydrolytic sol-gel chemistry. With chelation chemistry, a conformal
yet porous overcoat leads to a highly sintering-resistant Cu catalyst for liquid-phase
furfural hydrogenation. With the non-hydrolytic sol-gel route, a denser Al₂O₃
overcoat can be deposited to create a high density of Lewis acid-metal
interface sites over Pt/SBA-15. This overcoated Pt/SBA-15 has a substantially
increased hydrodeoxygenation activity for the conversion of lignin-derived
4-propylguaiacol into propylcyclohexane with up to 87% selectivity.