The behavior of catalyst surfaces is determined by the forming and breaking of bonds between the catalyst surface and the various intermediates along the pathway. This can be characterized by the adsorption energy of these intermediates. Adsorption energies of similar adsorbates are often strongly correlated across different metal surfaces; these relationships are known as scaling relations, and they lead to the development of the volcano plot. Volcano plots are useful in identifying promising catalyst surfaces, but also constrain the maximum catalytic performance. This work shows how the limitations of the volcano plot can be overcome by using metal alloys to break scaling relations. In this work, we demonstrate that breaking scaling relations can allow catalytic performance to exceed the maximum defined by a volcano plot. We used this principle to design novel alloy catalysts for methane steam reforming, which serves as a significant process in the production of hydrogen. An effective catalyst for this reaction should bind CH3 strongly, to promote C-H bond breaking in methane, but should bind C weakly, so that the surface is not poisoned by C. Therefore, we first searched for alloys with relatively strong CH3 adsorption and relatively weak C adsorption. We then performed explicit kinetic modeling on the most promising alloy surfaces, which showed a better performance than the volcano plot maximum, and hence outperformed the best pure metal catalysts, ruthenium and rhodium.

Exceeding the volcano plot maximum on alloy surfaces by breaking scaling relations

ACS Spring Meeting 2021

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