(731a) ALD Modified Au-Based Catalysts for Propylene Epoxidation

Propylene oxide (PO) is a chemical intermediate of great value and in high demand. It is used to produce useful polymeric materials. A direct catalytic epoxidation of propylene with hydrogen and oxygen to PO represents an environmentally friendly process and can be fulfilled over gold-titanium based catalysts. Isolation of the titanium was found to significantly reduce the cracking of propylene to ethanal and carbon dioxide.[1-2] However, these sites could gradually deactivate due to the change of titanium oxidation state and coordination, leading to low selectivity and coke formation. In addition, gold nanoparticles appear to sinter at high temperature, resulting in low activity.

In this work, the geometric effects of gold-titanium based catalysts are studied in detail using a number of characterization techniques such as in situ X-ray absorption spectroscopy and transmission electron microscopy. The loading and location of titanium are precisely controlled by means of atomic layer deposition (ALD). Reaction kinetics was measured using series of ALD modified catalysts to reveal possible reaction mechanisms. The location of the TiO₂ was found to alter the reactivity, selectivity and capability of catalyst regeneration.

References

[1] S. T. Oyama, Mechanisms in Homogeneous and Heterogeneous Epoxidation Catalysis. Elsevier, 2011.

[2] E. E. Stangland, B. Taylor, R. P. Andres, and W. N. Delgass, “Direct Vapor Phase Propylene Epoxidation over Deposition-Precipitation Gold-Titania Catalysts in the Presence of H2/O2: Effects of Support, Neutralizing Agent, and Pretreatment,” J. Phys. Chem. B, vol. 109, no. 6, pp. 2321–2330, Feb. 2005.