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Steering the Selectivity in Gold–Titanium-Catalyzed Propene Oxidation by Controlling the Surface Acidity

  • Ewoud J.J. de Boed
    Ewoud J.J. de Boed
    Materials Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, Utrecht 3584CG, The Netherlands
  • Jan Willem de Rijk
    Jan Willem de Rijk
    Materials Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, Utrecht 3584CG, The Netherlands
  • Petra E. de Jongh
    Petra E. de Jongh
    Materials Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, Utrecht 3584CG, The Netherlands
  • , and 
  • Baira Donoeva*
    Baira Donoeva
    Materials Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, Utrecht 3584CG, The Netherlands
    *Email: [email protected]
Cite this: J. Phys. Chem. C 2021, 125, 30, 16557–16568
Publication Date (Web):July 27, 2021
https://doi.org/10.1021/acs.jpcc.1c05503
Copyright © 2021 American Chemical Society
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Abstract

Supported nanoparticulate Au/Ti-SiO2 catalysts are a promising candidate for selective epoxidation of propene with H2/O2 mixtures. Here, we demonstrate that by altering the acidity of the surface titanol groups in Au/Ti-SiO2, the selectivity of these catalysts in propene oxidation can be controlled. That is, Au/Ti-SiO2 prepared using an alkali base during gold deposition shows basic properties due to the formation of Ti-ONa groups. The catalysts that contained Na+ and neutralized acid sites demonstrate high selectivity toward propene oxide. On the contrary, when the acidity of the Ti-OH groups is preserved by using NH4OH as a base during gold deposition, the catalyst is highly selective toward propanal at a similar propene conversion. This difference in selectivity is explained by the isomerization of initially formed propene oxide into propanal over acidic Ti-OH groups as we demonstrated using stacked bed experiments, where the Ti-support was exposed to propene oxide. When Na+ was present, no isomerization was observed, while without Na+ present, propene oxide was isomerized to propanal. In short, we demonstrate the crucial role of Na+ and acidic Ti-sites in steering the selectivity in gold-catalyzed propene epoxidation.

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  • Physisorption data, DR UV–vis data, XRD, Py-FTIR, additional STEM micrographs, EDS spectra, TGA-MS, additional XPS spectra, and additional catalysis data (PDF)

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