Molecular Beam Study of the CO Adsorption on a Regular Array of PdAu Clusters on Alumina

TL;DR

This study investigates how CO adsorption energy on PdAu clusters varies with gold surface concentration, revealing that ensemble effects dominate in reducing CO binding strength.

Contribution

It provides detailed kinetic analysis of CO adsorption on PdAu clusters with controlled composition and demonstrates the dominant role of ensemble effects in adsorption energy changes.

Findings

CO adsorption energy decreases with increasing Au surface concentration

Ensemble effects are the primary factor influencing adsorption energy reduction

The study quantifies CO lifetime variations across different cluster compositions

Abstract

The adsorption kinetics of CO on PdAu bimetallic clusters, containing 140 $\pm$ 12 atoms and a composition varying between 0% and 55% of Pd atoms, is investigated by a pulsed molecular beam method (MBRS). The clusters are grown on a nanostructured ultrathin film of alumina on Ni3Al (111) playing the role of a template which gives a hexagonal array of bimetallic clusters having a sharp size distribution and a uniform composition. The surface concentration calculated, assuming segregation of gold to the surface, varies between 0 and 90% of Au atoms on the surface. From the adsorption-desorption kinetics of CO, the lifetime of CO is measured at various temperatures. At low coverage, plotting the CO lifetime in an Arrhenius diagram one obtains the adsorption energy of CO. When the surface concentration of Au increases, the adsorption energy of CO on the PdAu clusters decreases. This evolution of the adsorption energy is discussed, from previous studies, in term of ligand and ensemble effects. We find that the ensemble effect plays a dominant role in the observed decrease of the adsorption energy of CO.