(731f) Enhanced Hydrothermal Stability of Phosphonate-Coated Al2O3 Supported Catalysts

Gamma phase alumina (γ-Al₂O₃) is a common catalyst support because its high abundance, mechanical and chemical stability, and high surface area, however, γ-Al₂O₃ is unstable in the presence of high temperature/high pressure steam used in aqueous phase reforming. Under these conditions, the support undergoes a phase transition to boehmite (AlO(OH)) accompanied with a significant loss in the support’s surface area as the pore structure deteriorates. Consequently, catalytic performance is greatly diminished as active metal clusters become less accessible or detach from support.

To prevent catalyst degradation, hydrophobic coatings can be deposited onto the Al₂O­₃ support for increased hydrothermal stability. Specifically, we chose to coat catalysts with phosphonic acids (PAs) since these capping agents selectively bind to the oxide support and form robust bonds with the surface. Additionally, the physical properties of catalysts can be further tuned by changing the phosphonate’s tail group.

In this work, we discuss recent results that have shown the deposition of alkyl phosphonic acids on alumina and supported catalysts drastically improves their hydrothermal stability. We examine how the alkyl tail length (or hydrophobicity) affects the suppression of boehmite formation and improves the retention of both metal and support surface areas. The beneficial roles of both phosphonate head and tail groups will be assessed as well as their impact on catalytic performance.