Accurate Adsorption Thermodynamics of Small Alkanes in Zeolites. Ab initio Theory and Experiment for H-Chabazite

Abstract

Heats of adsorption of methane, ethane, and propane in H-chabazite (Si/Al = 14.4) have been measured and entropies have been derived from adsorption isotherms. For these systems quantum chemical ab initio calculations of Gibbs free energies have been performed. The deviations from the experimental values for methane, ethane, and propane are below 3 kJ/mol for the enthalpy, and the Gibbs free energy. A hybrid high-level (MP2/CBS): low-level (DFT+dispersion) method is used to determine adsorption structures and energies. Vibrational entropies and thermal enthalpy contributions are obtained from vibrational partition functions for the DFT+dispersion potential energy surface. Anharmonic corrections have been evaluated for each normal mode separately. One-dimensional Schrodinger equations are solved for potentials obtained by (curvilinear) distortions of the normal modes using a representation in internal coordinates.

Hindered Translator and Hindered Rotor Models for Adsorbates: Partition Functions and Entropies

“…(39), and shown in Table 3 at these experimental conditions. As seen in Table 3, the errors in the translational entropies using the HO / 2D lattice gas approximation are rather small, averaging only 0.2 R per mode (x or y) for the four adsorbates using DFT with vdW corrections.…”

“…39 We used our new approach reported above to estimate the entropies of these alkanes on Pt(111) (with barriers estimated including vdW) but at the higher temperatures used in that…”

Reaction path analysis for 1-butanol dehydration in H-ZSM-5 zeolite: Ab initio and microkinetic modeling

“…A more accurate estimation of the entropic contributions could be obtained by accounting for anharmonicities by detailed scanning of the potential energy surface [60,61], but this would require significant computational efforts for large systems. Another approach to treat the low lying modes is the use of a frequency cutoff [ 44,56,57,62].…”

Impact of Zeolite Structure on Entropic–Enthalpic Contributions to Alkane Monomolecular Cracking: An IR Operando Study

“…[7,25] On the other hand, they do not confirmt he predictions that the alkane chain length and zeolite topology primarily influence the intrinsic activation energy and not the activation entropy. [35] Second, while our measurements explicitly probe the alkane-acid site complexes, the reactant state taken into account in simulations is defined by the AlÀC www.chemeurj.org atoms distance being lower than ag iven cut-off radius. [35] Second, while our measurements explicitly probe the alkane-acid site complexes, the reactant state taken into account in simulations is defined by the AlÀC www.chemeurj.org atoms distance being lower than ag iven cut-off radius.…”