(158e) Unconventional Pathways for Unconventional Feedstock: The Importance of Simultaneous Optimization of Catalytically Active Sites and Their Environment

In situ and operando spectroscopy and various theoretical tools have contributed a wealth of information regarding dominant reaction mechanisms and key intermediates of working heterogeneous catalysts. This knowledge has enabled the development of structure-function relationships and forms the basis for rational catalyst design. When it comes to unsolved problems in heterogeneous catalysis, however, limiting the search space to established mechanisms under traditional reaction conditions may prevent revolutionary discoveries. For example, natural gas may be reformed with H₂O or (partially) oxidized with O₂, but co-processing this feedstock with non-traditional oxidants is much less explored. Alternative mechanisms that prevail under non-traditional reaction conditions over novel catalyst materials that have not yet been tested are not easily anticipated. On the other hand, it is straightforward to consider a large number of possible elementary steps in kinetic models and assess the model sensitivity computationally. We will discuss such an approach starting from a basic microkinetic model for methane (partial) oxidation and reforming. The model is then augmented with additional elementary steps assuming they are quasi-equilibrated. Only those steps that are identified as kinetically relevant are then refined using density functional theory simulations. Using this procedure we discovered that silver-rich catalysts have the potential to be good methane oxidation catalysts in oxygen-rich reaction environments. Our findings agree well with a related approach using the degree of rate control to optimize the reaction conditions for butane partial oxidation to butanol over Ag₃Pd. Other implications are also discussed.