(575am) Targeted Ag Nano-Structures as Highly Selective Partial Oxidation Catalysts

Olefin epoxidation reactions involve partial oxidation of olefins to form epoxides. The catalyst used in this process is metallic Ag supported on inert supports. The critical issue in olefin epoxidation is the selectivity to epoxides. Recent studies have suggested that selectivity to epoxides is governed by a parallel reaction network in which surface oxametallacycle intermediates are isomerized on catalyst surface forming selective epoxide products and unselective aldehyde intermediates, which subsequently combust on the catalyst surface [1], [2] and [3].

We have utilized these molecular insights to show, via Density functional Theory (DFT) calculations, that the Ag(100) surface is inherently more selective than the Ag(111) surface. The main driving force for the enhanced selectivity of Ag(100) is a favorable interaction of this Ag surface with the oxametallacycle.

To test this hypothesis experimentally we have used recent advances in synthetic chemistry, which have laid the groundwork for the controlled synthesis of homogeneous nano-structures with well-defined surface facets. The polyol synthesis method was employed to control the growth of Ag nanostructures in solution yielding particles terminated in the (100) plane on most facets [4] and [5]. We have demonstrated that under steady state conditions the catalysts, which are rich in the (100), faces exhibit selectivities that are significantly higher that the selectivity of the catalysts which are dominated by the (111) facets.

REFERENCES

1. Linic, S., Barteau, M.A., JACS, 125, 4034 (2003).

2. Bocquet, M.L., Michaelides, A., et. al., JACS, 125, 5620 (2003).

3. Liu, X., Klust, A., Madix, R.J., Friend, C.M., J. Phys. Chem. C, 111, 3675 (2007).

4. Sun, Y., Xia, Y., Science, 298, 2176 (2002).

5. Sun, Y., Mayers, B., Herricks, T., Xia, Y., Nano Letters, 3, 955 (2003).