1 research outputs found
Effects of TiO<sub>2</sub> in Low Temperature Propylene Epoxidation Using Gold Catalysts
Propylene
epoxidation with molecular oxygen has been proposed as
a green and alternative process to produce propylene oxide (PO). In
order to develop catalysts with high selectivity, high conversion,
and long stability for the direct propylene epoxidation with molecular
oxygen, understanding of catalyst structure and reactivity relationships
is needed. Here, we combined atomic layer deposition and deposition
precipitation to synthesize series of well-defined Au-based catalysts
to study the catalyst structure and reactivity relationships for propylene
epoxidation at 373 K. We showed that by decorating TiO<sub>2</sub> on gold surface the inverse TiO<sub>2</sub>/Au/SiO<sub>2</sub> catalysts
maintained ∼90% selectivity to PO regardless of the weight
loading of the TiO<sub>2</sub>. The inverse TiO<sub>2</sub>/Au/SiO<sub>2</sub> catalysts exhibited improved regeneration compared to Au/TiO<sub>2</sub>/SiO<sub>2</sub>. The inverse TiO<sub>2</sub>/Au/SiO<sub>2</sub> catalysts can be regenerated in 10% oxygen at 373 K, while the Au/TiO<sub>2</sub>/SiO<sub>2</sub> catalysts failed to regenerate at as high
as 473 K. Combined characterizations of the Au-based catalysts by
X-ray absorption spectroscopy, scanning transmission electron microscopy,
and UV–vis spectroscopy suggested that the unique selectivity
and regeneration of TiO<sub>2</sub>/Au/SiO<sub>2</sub> are derived
from the site-isolated Ti sites on Au surface and Au–SiO<sub>2</sub> interfaces which are critical to achieve high PO selectivity
and generate only coke-like species with high oxygen content. The
high oxygen content coke-like species can therefore be easily removed.
These results indicate that inverse TiO<sub>2</sub>/Au/SiO<sub>2</sub> catalyst represents a system capable of realizing sustainable gas
phase propylene epoxidation with molecular oxygen at low temperature