Connecting Cation Site Location to Alkane Dehydrogenation Activity in Ni/BEA Catalysts

Carrie Farberow, Evan Wegener, Anurag Kumar, Jacob Miller, Daniel Dupuis, Seonah Kim, Daniel Ruddy

Research output: Contribution to journalArticlepeer-review

3 Scopus Citations

Abstract

Ni-modified beta zeolite (Ni/BEA) catalysts activate carbon-hydrogen bonds in light alkanes, as demonstrated through isobutane reaction testing. Controlled synthesis of Ni/BEA allows for efficient introduction of ion-exchanged Ni sites at varying Ni loadings (0.43% − 1.8%). These catalysts exhibit site time yields (STY) for H2 production that increase with increasing Ni loading. A detailed analysis of secondary reactions and carbon deposition based on the relative molar flowrates of product C and H indicates that the observed increase in H2 STY with increasing Ni loading is likely attributed to both increasing alkane activation activity and increasing formation of hydrogen-deficient aromatic products retained within the catalyst pores. In situ diffuse-reflectance UV–visible-NIR absorbance and X-ray absorption spectroscopies indicate isolated, 4-coordinate Ni(2+) species for all loadings. Quantum mechanics/molecular mechanics modeling identifies two distinct Ni(2+) sites consistent with the structural characterization, but with differing relative stabilities due to their coordination environment. Computed reaction energetics for isobutane dehydrogenation demonstrate that the more stable Ni(2+) species at a six-membered 4Si-2Al ring, Ni-6MR, is less active for isobutane dehydrogenation than the less stable Ni(2+) at the five-membered 3Si-2Al ring, Ni-5MR. The differing local structure of the isolated cationic Ni sites in Ni/BEA offers a possible rationalization for the increased H2 STY observed at greater Ni loadings.

Original languageAmerican English
Pages (from-to)264-273
Number of pages10
JournalJournal of Catalysis
Volume413
DOIs
StatePublished - 2022

Bibliographical note

Publisher Copyright:
© 2022 Elsevier Inc.

NREL Publication Number

  • NREL/JA-5100-79556

Keywords

  • Alkane activation
  • Beta
  • Dehydrogenation
  • Metal-modified zeolite
  • Nickel
  • Quantum mechanics/molecular mechanics
  • X-ray absorption spectroscopy

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