(640b) Probing the Gold Active Sites In Au/TS-1 for Gas Phase Epoxidation of Propylene In the Presence of Hydrogen
A single-step, direct catalytic partial oxidation of propylene to propylene oxide (PO) using molecular oxygen has long been desired as a greener and more economical process compared to the current PO production routes. By co-feeding hydrogen with propylene and oxygen and using Au/TiO2 as the catalyst, one can produce PO with high selectivity (~ 99%) at ambient pressure. However, the low PO rate (~10 gPO/h/kgCat), as well as poor catalyst stability, are short of the requirements for industrial application. The catalytic performance can be significantly improved by using TS-1(titanium silicalite-1) as the support for nano-gold clusters/particles such that the PO rate increases up to ~100 gPO/h/kgCat and the selectivity is maintained at ~ 80% PO. While gold particles with sizes in the range 2-5 nm in Au/TiO2 are assigned in the literature as the active sites in PO reaction, our previous work suggests that gold clusters smaller than 2 nm are much more active in propylene epoxidation. However, the issue of whether gold clusters inside the TS-1 micropores are active in the PO reaction has not been settled. This work addresses this question and attempts to further understand the gold active sites in Au/TS-1.
A TS-1 support coated with an inert layer of S-1 (silicalite-1) was designed and prepared for probing the activity of the gold clusters inside the TS-1 micropores for the PO reaction. This coated material (S-1/TS-1) was characterized via TEM, XRD, XPS, DRUV-vis and nitrogen adsorption analysis at LN2 temperature to understand the result of the silicalite-1 coating and the corresponding influence on the spatial distribution of