Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

John L. Falconer

Second Advisor

Alan W. Weimer

Third Advisor

David E. Clough

Fourth Advisor

J. Will Medlin

Fifth Advisor

Ronggui Yang

Abstract

Cobalt catalysts were prepared on porous Al2O3 and W/Al2O3 supports by atomic layer deposition (ALD) that used sequential reactions of cobaltocene (CoCp2) and H2 at 483 to 523 K. This preparation method avoided formation of an intermediate oxide, so the catalysts could be activated at lower temperatures. Some of these catalysts had CO reaction rates per g of Co in Fischer-Tropsch synthesis (FTS) that were three times those reported for Co catalysts prepared by incipient wetness. The FTS reacts CO and H2 to form hydrocarbon liquids that can used as synthetic fuels. The rate of FTS depended on the number of ALD cycles, and catalysts prepared with one cycle had activities equivalent to incipient wetness Co catalysts; the highest reaction rate per g of catalyst was obtained for catalysts prepared using four ALD cycles. Two types of Co were observed on the alumina surface using TEM: Co particles with diameters between 0.6 and 1.8 nm (75% were smaller than 1 nm), and Co crystalline planes that were as large as 35 nm. Cobalt catalysts prepared by ALD retained adsorbed ligands that appeared to be stable for at least eight months at room temperature.

Tungsten was deposited onto porous Al2O3 by ALD to provide a catalyst support with higher thermal conductivity because the FTS reaction is highly exothermic. The W indeed increased thermal conductivity, and the resulting supports were used for Co ALD following deposition of an Al2O3 ALD layer. However, although Co deposits on ALD Al2O3, the Co had no activity for FTS, apparently because the ALD Al2O3 was amorphous. In contrast ALD Al2O3 that was heat treated at high temperature was partially crystalline and served as a support for an active FTS catalyst.

Share

COinS