Accurate Prediction of Hydrocarbon Interactions with Zeolites Utilizing Improved Exchange-Correlation Functionals and QM/MM Methods: Benchmark Calculations of Adsorption Enthalpies and Application to Ethene Methylation by Methanol

Abstract

The adsorption enthalpy of light hydrocarbon molecules in both acidic and neutral zeolite MFI has been investigated with a range of computational methods. The role of cluster model size and density functional theory methodology is examined by comparison with high quality ab initio wave function theory MP2 results and experimentally determined heats of adsorption. The commonly applied B3LYP functional performs poorly in benchmark studies due to an inadequate description of intermolecular interactions. The functionals ωB97X-D and M06-2X predict adsorption enthalpies consistent with experimental values over three classes of adsorbates. A hybrid quantum mechanics/molecular mechanics (QM/MM) method is required to converge calculated thermochemical properties with respect to cluster model size in a manner that is computationally efficient. The accuracy of both QM and QM/MM methods is highly sensitive to choice of level of theory and cluster size, requiring the use of large basis sets, large cluster models, and ...