Metal nanoparticles dispersed across support surfaces form the basis for many industrial catalysts and electrocatalysts. These will play an ever increasing role in the future of clean energy and environmental technology. Our calorimetric measurements of metal atom adsorption energies on support surfaces have allowed us to determine both the chemical potential (μ) of metal atoms in supported nanoparticles versus particle size and the adhesion energies (Eadh) of metal nanoparticles to different support surfaces. We find that this chemical potential varies with effective particle diameter (D) as: μ(D) = [(3γm – Eadh)(1 + Do/D)](2Vm / D), where γm is the surface energy of the bulk metal, Do is ~1.5 nm, and Vm is the molar volume of the bulk metal. Metal chemical potential is a key descriptor for understanding catalytic performance, since it correlates with the binding strengths of adsorbed reaction intermediates to the nanoparticles. It also enters directly into rate equations for catalyst sintering, which are essential for predicting the long-term stability of supported nanoparticles. On a given oxide support surface, metal/support adhesion energies are found to increase with the catalyst elements’ oxophilicity, defined here as the heat of formation of its most stable oxide from a gaseous metal atom plus O2 gas. Other trends in adhesion energies will also be discussed. Metal chemical potential is also an important descriptor for bimetallic and alloy catalysts.

Adhesion energies of metal nanoparticles to catalyst support surfaces: Relationships to metal atom chemical potential, catalyst activity, and lifetime

2019 Fall National Meeting

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