Hydrogen Adsorption at the Au/TiO2 Interface: Quantitative Determination and Spectroscopic Signature of the Reactive Interface Hydroxyl Groups at the Active Site

Akbar Mahdavi-Shakib, Lauren C. Rich, Todd N. Whittaker, Bert D. Chandler

Research output: Contribution to journalArticlepeer-review

Abstract

Infrared spectroscopy shows that H2 adsorbs heterolytically at the metal–support interface (MSI) of Au/TiO2 catalysts. This generates stable protonated MSI hydroxyls, which are chemically distinct from adsorbed water and free surface hydroxyls. IR spectra collected during H2 adsorption revealed changes associated with the loss of unprotonated interface hydroxyls (MSITiOH) and the appearance of protonated interface hydroxyls (MSITiOH2+). This allowed us to identify a spectroscopic signature associated with MSI hydroxyls interacting with Au nanoparticles and separate that signature from the unmodified hydroxyls that dominate the surface. Prior to H2 adsorption, MSI hydroxyls are electron-rich relative to other surface hydroxyls on the catalyst. As a consequence, MSI hydroxyls are more basic, which likely contribute to their involvement in H2 activation. The surface density of the MSITiOH2+ species was quantified with the broad-background absorbance (BBA) associated with electron injection into the support during H2 adsorption. Quantifying these signals across a series of catalysts showed that each Au perimeter atom is associated with one reactive MSITiOH group. This unexpected result indicates that Au modifies the local structural and electronic properties of the support. Thus, the synergism between Au and TiO2 produces electron-deficient Au particles, which are stronger Lewis acids, and increases the number of electron-rich MSI hydroxyls, which are stronger Brønsted bases.

Original languageEnglish (US)
Pages (from-to)15194-15202
Number of pages9
JournalACS Catalysis
Volume11
Issue number24
DOIs
StatePublished - Dec 17 2021

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)

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