The Significant Differences in Solvation Thermodynamics of C1-C3 Oxygenates in Hydrophilic versus Hydrophobic Pores of a Hydrophilic Ti- FAU Zeolite Model

XT Chen and RB Getman, JOURNAL OF PHYSICAL CHEMISTRY C, 128, 19367-19379 (2024).

DOI: 10.1021/acs.jpcc.4c04596

The rates of catalytic reactions have been observed to be dramatically different in zeolites, depending on whether they are hydrophobic or hydrophilic. Hypotheses aimed at explaining this behavior have pointed to various solvent and zeolite properties as having an influence on entropy. Herein, the influence of various solvent and adsorbate properties on the solvation energies, entropies, and free energies of 11 C1-C3 oxygenates in hydrophobic and hydrophilic pores within a hydrophilic model of Ti-FAU zeolite is tested. The results indicate significant variation in the solvation thermodynamics depending on the adsorbate type as well as if it is bound within a hydrophobic or hydrophilic pore. Further, while solvation energies are related to solvent-adsorbate interactions, solvation entropies have multiple contributions, and these differ depending on whether the adsorbate is in a hydrophobic or hydrophilic pore. Specifically, solvation entropies in hydrophobic pores are related to solvent structural properties, whereas solvation entropies in hydrophilic pores are related to adsorbate polarity. The large range of results obtained from two different pores within one zeolite model with minimal unique adsorption sites suggests that solvation behavior in zeolites is complicated and that the phenomena that control the observed performance depend on the zeolite, reaction, and solvent.

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