TY - JOUR
T1 - Steering the Selectivity in Gold-Titanium-Catalyzed Propene Oxidation by Controlling the Surface Acidity
AU - De Boed, Ewoud J.J.
AU - De Rijk, Jan Willem
AU - De Jongh, Petra E.
AU - Donoeva, Baira
N1 - Funding Information:
The authors acknowledge funding from Utrecht University. The authors would like to thank Petra Keijzer and Lars van der Wal for the electron microscopy images of the prepared materials, Dennie Wezendonk for performing TGA-MS, Pascal Wijten for helping with GC, and Nikos Nikolopoulos for N physisorption, and Petra Keijzer is also thanked for the fruitful discussions. Dr. Nikolay Kosinov (Technical University Eindhoven) is acknowledged for the XPS measurements. 2
Publisher Copyright:
© 2021 American Chemical Society.
PY - 2021/8/5
Y1 - 2021/8/5
N2 - 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.
AB - 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.
U2 - 10.1021/acs.jpcc.1c05503
DO - 10.1021/acs.jpcc.1c05503
M3 - Article
AN - SCOPUS:85112500615
SN - 1932-7447
VL - 125
SP - 16557
EP - 16568
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 30
ER -