(330a) A Systematic Ab Initio Strategy for Predicting Structure-Activity Relationships of Catalysts On Amorphous Supports

Methods for modeling catalytic sites on amorphous supports lag far behind methods for modeling catalytic sites on metal surfaces, zeolites, and other crystalline materials. Typical ad hoc strategies use cluster models with arbitrarily chosen constraints to model the rigid amorphous support, and these constraints influence properties to the site. Alternatively no constraints are used, which results in catalytic sites with unrealistic flexibility. We present a systematic ab initio method to model isolated active sites on amorphous supports using small cluster models. To avoid arbitrary constraints while still retaining influences from the extended solid structure, we introduce a quenched disorder embedding scheme based on the reversible work theorem. A sequential quadratic programming framework then helps us test mechanistic hypotheses and relate chemical properties, such as the activation energy, to active site structure. The algorithm is illustrated on an Empirical Valence Bond model energy landscape and its limitations are discussed. We also use the algorithm to model an off-pathway kinetic trap in olefin metathesis by isolated Mo sites on amorphous SiO₂.