Catalyst Thickness Can Tune Adsorption

Controlling the state of a molecule adsorbing onto a catalyst surface is an important part of improving catalyst performance. Now, a research group led by David E. Starr of Brookhaven National Laboratory and Hendrik Bluhm of Lawrence Berkeley National Laboratory has found that NO₂ forms NO₂^– when adsorbed onto MgO films only two monolayers thick (J. Phys. Chem. C, DOI: 10.1021/jp900410v). For MgO films thicker than five monolayers, however, NO₂ converts to NO₃^–, as is the case for bulk MgO. The MgO films were supported on a silver substrate, and the researchers also observed changes at the MgO/Ag interface when NO₂ adsorbed onto thinner films. That result, along with prior computational work, led the researchers to conclude that the presence of the metal substrate modifies the adsorption properties of NO₂, leading to the charge transfer to NO₂ and the overall stabilization of the system. The results demonstrate that it is possible to tune the adsorption properties of molecules, as well as deposited metals, by controlling the thickness of thin oxide films, the authors say.