Date of Award
Doctor of Philosophy (PhD)
Chemical and Biomolecular Engineering
Raymond J. Gorte
Deactivation of catalytic functional oxides through the loss of surface area is a major concern. The conventional approach to maintain high-surface area of these materials is to incorporate the functional components onto a support which is less susceptible to sintering. Conventional impregnation tends to introduce large crystallites and often does not increase the surface area of the functional component. To address this issue, ALD was used in this work to engineer materials on the surface of interest.
ALD has been used to form uniform oxides in a layer-by-layer manner with excellent compositional control. However, since ALD was developed in the semi-conductor industry to produce relatively thick films on a flat surface, the design criteria are very different from what is required for catalytic applications. First, the rapid cycling with high-velocity carrier gases that are commonly used in semiconductor fabrications will create diffusion limitations in porous structures. Second, when carrier gases are used, most reagents pass through the reactor without being incorporated into the sample. This is prohibitively expensive for catalytic applications. In this thesis, a static ALD system which avoids these issues was developed for preparing catalysts in two primary areas: (a) high-surface area active supports with excellent thermal stability, and (b) stabilization of precious metals.
The first area involved fabricating thin films of Fe2O3, CeO2, CeZrO4, and LaFeO3 on porous Al2O3. These high-surface area films were shown to be uniform and they exhibited excellent thermal stability up to 1273 K when used as supports for Pd in methane and CO oxidation. With compositional control by ALD, CeZrO4 and LaFeO3, complex oxides would otherwise require complex synthesis or high temperature treatments, were easily fabricated at moderate conditions.
The second area involved stabilizing metal particles by thin films of LaFeO3 and ZrO2 prepared by ALD. Pd supported on LaFeO3 is of interests as it is the classical example of a “smart” catalyst capable of redispersing metal particles following redox cycling conditions. The LaFeO3 catalysts were shown to exhibit properties expect for smart catalysts. Overcoating thin films of ZrO2 on Pd to improve its thermal stability was also demonstrated.
Onn, Tzia Ming, "Preparation Of Active And Stable High-Surface Area Catalysts By Atomic Layer Deposition" (2018). Publicly Accessible Penn Dissertations. 2952.