CBE Doctoral Dissertation Defense: “High-Pressure Reactions on Metals and Metal Oxides in Mesoporous Silica” (Ching-Yu Wang)

Abstract:

SBA-15, a type of mesoporous silica, is an attractive support for heterogeneous catalysts due to its high surface area, one-dimensional uniform pore structure, and high thermal stability. However, modifying SBA-15 with metal and metal oxide using conventional wetness incipient impregnation is challenging. In this thesis, Atomic Layer Deposition (ALD) was used to prepare catalysts on SBA-15. Through multiple cycles of ALD, various metal oxides can be uniformly deposited in the pores of SBA-15 as thin films, while maintaining the high surface area and well-defined mesoporous structure. Using vapor-phase infiltration, i.e., one ALD cycle, a wide range of metals can be efficiently incorporated into the SBA-15 pores, exhibiting high metal loadings and metal nanoparticle sizes of 3 to 4 nm.

The catalytic properties of the SBA-15-supported catalysts were investigated for dehydrogenation of cycloalkanes and hydrodeoxygenation of m-cresol. While Pt/SBA-15 deactivated rapidly at low pressures due to coking, it remained stable for long periods when the pressure was above certain critical values. These critical values depended on the pore size and structure of the support and the reaction temperature. It was demonstrated that hydrodeoxygenation of m-cresol, a model compound for phenolics, can be carried out over WOx-Pt/SBA-15 in a stable manner using alkanes as H2 carriers. Additionally, cycloalkane dehydrogenation over Pt/SBA-15 was found to be stable at high pressure, thereby providing high endothermicity.

Finally, the growth of metal oxides and their interactions with SBA-15 were studied. It was found that the surface silanol groups of SBA-15 were critical for stabilizing WO3 in the mesopores. CeO2 films supported by SBA-15 were more reducible than their bulk counterparts or ceria supported by Al2O3 due to a reaction between ceria and silica.