Capturing the Coverage Dependence of Aromatics Via Mean-Field Models: Application in the Hydrodeoxygenation of Biofuels

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  • Type:
    Conference Presentation
  • Conference Type:
    AIChE Annual Meeting
  • Presentation Date:
    November 8, 2021
  • Duration:
    18 minutes
  • Skill Level:
    Intermediate
  • PDHs:
    0.50

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Hydrodeoxygenation is a process in which oxygen is removed from biofuel-derived compounds, represented here as oxygenated aromatics, via catalytic hydrogenation and C-O bond cleavage. The exact reaction pathways for such upgrading have been computationally modeled on a vast array of catalysts. However, a critical concern with many such models is the lack of coverage effects when mapping reaction pathways, which can potentially impact the accuracy of the predicted dominant pathways and rate limiting steps. Here, we determine the effect of coverage on the adsorption energies of a range of oxygenated aromatics (i.e. benzene, phenol, guaiacol, etc.) on Pt(111) and Ru(0001) using density functional theory (DFT) with van der Waals effects included.

Using the results from this study, we have derived three key insights into the coverage dependence of oxygenated aromatics. As can be seen in Figure 1, closed shell adsorbates (i.e. benzene, phenol, anisole, etc.) have significant repulsive interactions (i.e. adsorption energy weakens with increasing coverage), while adsorbates with free radicals, i.e. phenoxy, see nearly flat mean-field slopes, indicating that there is a minimal coverage effect on these systems. Second, increasing the size of the functional group from hydroxyl (phenol) to methoxyl (anisole) results in an increase in the mean-field slope by ~50%, demonstrating that the change in functional group can significantly increase the repulsive lateral interactions in the system. Third, the mean-field slopes for all adsorbates are 2-7 times higher on Pt(111) as compared to Ru(0001), which suggests that the adsorbate-metal interaction governs the lateral interactions and that higher oxygenated adsorbate coverages are likely on Ru(0001). Upon completion of the mean-field coverage parameterization of all oxygenated adsorbates, the mean-field dependence will be rationalized via the d-band model. Additionally, a simplified lattice gas cluster expansion model will be applied to better capture and explain the lateral interactions within these systems.

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