Investigating Deposition Sequence During Synthesis of Pd/Al2O3 Catalysts Modified with Organic Monolayers

Zachary Blanchette, Jing Zhang, Sadegh Yazdi, Michael Griffin, Daniel Schwartz, J. Medlin

Research output: Contribution to journalArticlepeer-review

4 Scopus Citations

Abstract

Modification of supported metal catalysts with self-assembled monolayers (SAMs) has been shown to improve selectivity and turnover frequencies (TOFs) for many catalytic reactions. However, these benefits are often accompanied by a decrease in overall mass activity due to partial blocking of active sites by the monolayers. Therefore, a potential method for increasing site accessibility is to deposit the active metal (e.g., Pd) after deposition of a SAM modifier on the support material. In this work, Pd/Al2O3 catalysts were synthesized using both a conventional, “metal-first” sequence in which the phosphonic acid (PA) SAM was deposited on Pd/Al2O3 and a “SAM-first” technique in which the ligands were deposited onto the support prior to deposition of the metal. Although metal-first catalysts showed a significant increase in TOF during benzyl alcohol HDO, they exhibited only a modest increase in overall mass activity due to a decrease in the number of active sites. Meanwhile, SAM-first catalysts showed similar improvements in TOF and toluene selectivity but exhibited significantly improved HDO rates compared to metal-first catalysts. The rate increase was attributed to reduced site blocking as evidenced by CO chemisorption measurements. Additionally, analysis of catalysts having high Pd loadings using transmission electron microscopy (TEM) showed that SAM-first catalysts generally resulted in lower average particle sizes than traditionally modified and unmodified catalysts, suggesting that precoating the support surface with PAs changes the way that Pd is deposited during incipient wetness, leading here to improved activity.

Original languageAmerican English
Pages (from-to)2306-2314
Number of pages9
JournalCatalysis Science and Technology
Volume12
Issue number7
DOIs
StatePublished - 21 Feb 2022

Bibliographical note

Publisher Copyright:
© 2022 The Royal Society of Chemistry.

NREL Publication Number

  • NREL/JA-5100-82844

Keywords

  • catalytic reactions
  • deposition
  • self-assembled monolayers
  • turnover frequencies

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