2019 AIChE Annual Meeting

(629d) Brønsted Acid Sites on Tungsten Oxide/Platinum Catalysts

Authors

Shizhong Liu - Presenter, University of Delaware
Jiayi Fu, University of Delaware
Weiqing Zheng, University of Delaware
Stavros Caratzoulas, University of Delaware
Dionisios G. Vlachos, University of Delaware
Tungsten oxides (WO3) on platinum (Pt), represented as WOx/Pt, have shown great activity and selectivity in hydrodeoxygenation (HDO) reactions [1]. The formed solid acid sites on the oxides in H2 have been speculated to lead to the significant performance. However, the fundamental understanding of these solid acids is insufficient. One complication is that WOx/Pt may have different acid sites, i.e., the Brønsted and the Lewis acid sites. Considering the complexity of the metal oxides/metal interface under reaction conditions, direct observations are lacking. Thus, a theoretical approach can provide insights into the formation of acid sites in WOx/Pt catalysts. Our study focuses on the Brønsted acid sites of WOx/Pt, including the formation, spatial distribution and catalytic activity.

Spin-polarized DFT calculations have been performed using VASP [2]. Exchange and correlation effects have been approximated with the PBE functional [3]. We applied Monkhorst-Pack [4] mesh k-points of (3 × 2 × 1) for surface calculations. DFT results are used in the pMuTT[6] thermochemistry toolbox to estimate rate constants.

Our DFT calculations found two possible ways to generate Brønsted acid sites with a barrier smaller than 0.5 eV, indicating that the acid formation can occur easily. The reaction network of IPA dehydration reaction on hydrogenated W3O9x/Pt was built with data from geometry optimization and transition states search carried out using VASP. Deprotonation energies were calculated as a descriptor to estimate the acidities. We found a positive correlation between the deprotonation energies and IPA dehydration barriers.

References

  1. Wang, C., Mironenko, A. V., Raizada, A., Chen, T., Mao, X., Padmanabhan, A., Vlachos, D.G., Gorte, R.J. and Vohs, J.M. et al. ACS Catalysis9 (2018): 7749-7759
  2. Kresse, G.; Hafner, J. Phys Rev B 1993, 47, 558; Kresse, G.; Furthmuller, J. Phys Rev B 1996, 54, 11169.
  3. Perdew, John P., Kieron Burke, and Matthias Ernzerhof, Rev. Lett.77.18 (1996): 3865.
  4. Monkhorst, H. J.; Pack, J. D. Rev. B 1976, 13, 5188.
  5. Henkelman, G.; Jonsson, H. Chem. Phys. 2000, 113, 9978−9978
  6. https://pypi.org/project/pMuTT/