Shape-selective sieving layers on an oxide catalyst surface

• Christian P. Canlas,
• Junling Lu,
• Natalie A. Ray,
• Nicolas A. Grosso-Giordano,
• Sungsik Lee,
• Jeffrey W. Elam,
• Randall E. Winans,
• Richard P. Van Duyne,
• Peter C. Stair
• & Justin M. Notestein

Nature Chemistry

 

(2012)

 

doi:10.1038/nchem.1477

Received

 

15 June 2012 

Accepted

 

11 September 2012 

Published online

 

28 October 2012

New porous materials such as zeolites, metal–organic frameworks and mesostructured oxides are of immense practical utility for gas storage, separations and heterogeneous catalysis. Their extended pore structures enable selective uptake of molecules or can modify the product selectivity (regioselectivity or enantioselectivity) of catalyst sites contained within. However, diffusion within pores can be problematic for biomass and fine chemicals, and not all catalyst classes can be readily synthesized with pores of the correct dimensions. Here, we present a novel approach that adds reactant selectivity to existing, non-porous oxide catalysts by first grafting the catalyst particles with single-molecule sacrificial templates, then partially overcoating the catalyst with a second oxide through atomic layer deposition. This technique is used to create sieving layers ofAl₂O₃ (thickness, 0.4–0.7 nm) with ‘nanocavities’ (<2 nm in diameter) on a TiO₂ photocatalyst. The additional layers result in selectivity (up to 9:1) towards less hindered reactants in otherwise unselective, competitive photocatalytic oxidations and transfer hydrogenations.