CO adsorption on supported gold nanoparticle catalysts: Application of the temkin model

The adsorption of CO on the supported gold nanoparticle catalysts Au/TiO ₂, Au/Fe ₂O ₃, and Au/ZrO ₂ was examined using infrared transmission spectroscopy to quantify the isobaric CO coverage as a function of temperature. The Temkin adsorbate interaction model was then applied to account for the adsorption behavior. To test the general applicability of the Temkin model, this treatment was also applied to three data sets from the literature. This included another real-world catalyst and two model catalysts. All data sets were accurately represented by the Temkin adsorbate interaction model. The resulting thermodynamic metrics are consistent with previous determinations and reflect a particle size-dependence. In particular, the intrinsic adsorption enthalpy at zero CO coverage varies almost linearly with Au particle size, and this trend appears to be correlated with the abundance of low-coordinate Au sites (cf., CN = 6 and 7 for corners and edges, respectively). For very small particles with mostly CN = 6 corner sites, the enthalpy reflects strong binding (cf., -ΔH ₀ ≈ 78 kJ/mol), while for large particles with mostly CN = 7 edge sites, the enthalpy reflects weaker binding (cf., -ΔH ₀ ≈ 63 kJ/mol). The results also suggest that these sites are coupled. This study demonstrates that the Temkin adsorbate interaction model accurately represents adsorption data, yields meaningful metrics that are useful for characterizing nanoparticle catalysts, and should be applicable to other adsorption data sets.