How strain can break the scaling relations of catalysis

Heterogeneous catalysts control the rates of chemical reactions by changing the energy levels of bound intermediates relative to one another. However, the design flexibility in catalysis is limited by scaling relations: when a catalyst binds one adsorbate more strongly, it tends to bind similar adsorbates more strongly as well. Here we show how strain can break this constraint by employing a mechanics-based eigenstress model to rationalize the effect of strain on adsorbate–catalyst bonding. This model suggests that the sign of the binding-energy response to strain depends on the coupling of the adsorbate-induced eigenstress with the applied strain; thus, tensile strain can make binding either stronger or weaker, depending on the eigenstress characteristics of the adsorbate on the surface. We then suggest how these principles can be used in conjunction with anisotropic strain to engineer opposite responses of adjacent adsorbates to strain; such effects are expected to allow larger changes to reaction rates than predicted by scaling relations. Scaling relationships provide powerful predictive opportunities in catalysis, but at the same time also reflect the limitations related to the design of new catalytic systems. Now, theoretical studies show how mechanical strain on catalyst surfaces can be engineered to break scaling relations.