Abstract
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 TiO2 on gold surface the inverse TiO2/Au/SiO2 catalysts maintained ∼90% selectivity to PO regardless of the weight loading of the TiO2. The inverse TiO2/Au/SiO2 catalysts exhibited improved regeneration compared to Au/TiO2/SiO2. The inverse TiO2/Au/SiO2 catalysts can be regenerated in 10% oxygen at 373 K, while the Au/TiO2/SiO2 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 TiO2/Au/SiO2 are derived from the site-isolated Ti sites on Au surface and Au-SiO2 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 TiO2/Au/SiO2 catalyst represents a system capable of realizing sustainable gas phase propylene epoxidation with molecular oxygen at low temperature.
| Original language | English |
|---|---|
| Pages (from-to) | 1688-1698 |
| Number of pages | 11 |
| Journal | Journal of Physical Chemistry C |
| Volume | 122 |
| Issue number | 3 |
| DOIs | |
| State | Published - Jan 25 2018 |
Funding
This work is sponsored by the National Science Foundation (Grants CBET-1511820 and CBET-1510485). The authors thank Johnny Goodwin of University of Alabama for taking the STEM images. Part of the work including the BET surface area measurements and UV−vis spectroscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. This work is sponsored by the National Science Foundation (Grants CBET-1511820 and CBET-1510485). The authors thank Johnny Goodwin of University of Alabama for taking the STEM images. Part of the work including the BET surface area measurements and UV-vis spectroscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357.