The Site‐Assembly Determines Catalytic Activity of Nanoparticles

Abstract

Heterogeneous catalysts are often designed as metal nanoparticles supported on oxide surfaces.H ere,t he relation between particle morphology and reaction kinetics is investigated by scaling relation kinetic Monte Carlo simulations using CO oxidation over Pt nanoparticles as amodel reaction. We find that different particle morphologies result in vastly different catalytic activities.The activity is strongly affected by kinetic couplings between sites,a nd aw ide site distribution generally enhances the activity.The present study highlights the role of site-assemblies as aconcept that, in addition to isolated active sites,c an be used to understand catalytic reactions over nanoparticles.Heterogeneous catalysts are commonly realized as metal nanoparticles supported on oxide-surfaces.The nanoparticles in technical catalysts are generally ill-defined with respect to shape and size,a nd the contribution of different particle geometries and sizes to the measured catalytic activity is difficult to disentangle.T he situation can be further complicated by changes in particle shape arising in response to the reaction conditions. [1-3] As particle shape may affect catalytic activity,itbecomes important to understand the link between particle morphology and catalyst performance.T his topic, although central, has not received much systematic attention. Experimental studies of multiple reactions have revealed size and shape dependencies of the activity. [4][5][6][7] Theoretically, density functional theory [8,9] (DFT) calculations have outlined how adsorption properties depend on particle geometry, [10,11] which has been rationalized by descriptors such as coordination numbers and d-band centers. [12][13][14][15] Structure sensitivity in the catalytic activity has generally been investigated by dividing the catalyst into isolated facets with one type of site. [13,16] However,t reating sites as isolated entities implies that kinetic couplings between the sites are neglected. CO oxidation is ap rototypical model reaction, for which microkinetic models have predicted reactivity and size dependence for different metal particles. [17,18] However,these models were formulated in the mean field approximation (MFA), which does not account for the specific arrangement and detailed kinetic couplings of sites.T he importance of as ite distribution, or site-assembly,h ave previously been recognized as complex kinetic couplings,b oth experimentally [19] and by schematic kinetic Monte Carlo simulations. [20] These studies indicate that the site-assembly can be crucial for the reaction kinetics,h owever without quantitative estimates.T hus there is agap in the understanding of the relation between particle morphology and catalytic activity.Thepresent article explores the relation between particle geometry and catalytic activity,b yp resenting first-principles kinetic Monte Carlo simulations over nanoparticles of different shapes,u sing CO oxidation over Pt nanoparticles as an archetype reaction. We find that identical sites on different geome...

Assessing Catalytic Rates of Bimetallic Nanoparticles with Active Site Specificity - A Case Study using NO Decomposition

“…Site resolved descriptors have been used to design nanoparticles for monometallic catalysts. 17,24,25 Bimetallic catalysts impose an altogether different challenge, due to the heterogeneous distribution of active sites and a vast combinatorial space of materials. It is still a challenge, however, to translate these descriptors into active site-resolved reaction kinetics across the distribution of active sites ubiquitous on bimetallic nanoparticles.…”