Chapter 5. The correspondence of calorimetric studies with DFT simulations in heterogeneous catalysis

Abstract

Molecular modeling, being computationally intensive, started with simple molecules and several atom clusters. Given that surface sites in heterogeneous catalysts involve complex structure, multielement mixtures, the effects of coverage, coadsorbates, and support interaction, simulations must continue to evolve in sophistication. An essential aspect is to build and validate these models with direct experimental evidence from calorimetric and spectroscopic results. In this regard, experimental heats of adsorption from single-crystal adsorption calorimetry and Tian-Calvet microcalorimetry on porous catalysts serves to benchmark the energies predicted by density functional theory (DFT) simulations, which are dependent upon the particular exchange functionals. The development of energy of adsorption databases is a key to improve the sophistication of DFT simulations. Adsorption databases to-date have focused on single crystal metal surfaces. Experience with modeling the energetics of even simple molecule adsorption on single crystal and supported metal catalyst surfaces has motivated the development of increasingly sophisticated DFT models. The particular case study of CO adsorption documents the challenges associated with developing DFT models that agree with experimental energetics. Studies with zeolites have shown that the van der Waals term associated with adsorbate-wall interactions must be incorporated into the DFT model for better agreement between prediction and experimental calorimetric data. This interaction is specific to the micropore structure and quantifying its contribution serves with heat of adsorption data to quantify the energetics of reactive intermediates in microporous structures.