Porosity Promotes Selectivity

A templating process that creates a porous surface layer adds new reactant selectivity to robust metal-oxide catalysts, chemists report (Nat. Chem., DOI: 10.1038/nchem.1477). Supported and bulk oxides catalyze a variety of economically important reactions. Although the oxides may target specific functional groups, they typically can’t discriminate by molecule size, as crystalline microporous materials do. A group led by Northwestern University’s Justin M. Notestein has now developed a way to include size selection by using atomic layer deposition to add a porous film on top of oxide catalyst particles. Notestein and colleagues attached bulky, poorly packed templating ligands to the surface of TiO₂ particles. They then added a thin, inert Al₂O₃ layer that adhered to the TiO₂ and surrounded the template molecules. Removing the template molecules left cavities 2 nm wide and 2 nm deep. The researchers used the porous-layer-coated particles to selectively photooxidize benzyl alcohol over 2,4,6-trimethylbenzyl alcohol and reduce nitrobenzene over nitroxylene.