Increasing the Hydrothermal Stability of Alumina Based Catalysts

Aqueous phase processes are expected to play a key role in future biorefineries. This environment leads to new requirements for the stability of heterogeneous catalysts because many of these materials were developed for gas phase reactions. Recently, it was demonstrated that γ-alumina supports are converted into a crystalline boehmite phase [1]. This transformation results in a drastic decrease of the surface and the concentration of accessible Lewis acids sites.

The conversion of γ-alumina to boehmite is significantly retarded when supported Pt or Ni particles are present on the support because the metal particles block surface hydroxyl group. These groups also serve as initiation sites for the hydration of γ-alumina to boehmite. To eliminate the remaining surface hydroxyl groups Pt/γ-Al₂O₃ catalysts were capped. Boehmite formation was not observed for any of the protected samples and a significantly increased hydrogen production was observed when the catalysts were used for aqueous phase reforming of sorbitol. Increased stability was also observed for amorphous silica-alumina supports that were synthesized under well controlled conditions.

Reference:

[1]        R.M. Ravenelle, J.R. Copeland, W.-G. Kim, J.C. Crittenden, and C. Sievers, ACS Catalysis 1 (2011) 552-561.