This thesis summarizes our research efforts on the application of the nano-structured anodic aluminum oxide (AAO) membrane in heterogeneous catalysis. Procedures for growing the AAO membrane in the center of an aluminum disc have been developed by appropriately masking the disk's perimeter during the anodization and etching steps. The remaining aluminum ring connects seamlessly to the AAO and serves as a support for the membrane. The supported AAO membrane can be sealed in a flow reactor so that the nanopores on the membrane function as a parallel array of tubular reactors. Coating catalytically active materials onto the walls of the nanopores turns the AAO membrane into a novel catalytic system. In the cyclohexane oxidative dehydrogenation (ODH) reaction, the membrane catalytic system demonstrates advantages over the conventional powder bed in terms of overcoming bypass and diffusion limitations, reducing over oxidation, and inhibiting undesired gas phase reactions. The ordered one-dimensional nanopores make the AAO membrane an ideal substrate for fabrication of catalysts by atomic layer deposition (ALD). The catalytic performances of vanadium oxide (VOx) catalysts deposited on the membranes by ALD and by incipient wetness impregnation are compared in the ODH of cyclohexane. The ALD VOx show higher activity than the impregnated VOx, which reflects the better dispersion of the catalytic species as synthesized by ALD. In the same range of VOx loadings, distinct catalytic activities resulting from different structures of the catalytic sites are more evident on the samples prepared by multiple cycles of ALD, implying that the form of the supported catalyst can be better controlled by applying the ALD technique. The ODH of cyclohexane is studied in detail over the ALD synthesized VOx catalysts. At low loadings of the catalyst, the supported VOx are mostly in the isolated state; the polyvanadate domains are formed as the vanadium content increases. In the cyclohexane ODH reaction, the polyvanadate sites are shown to be more active than the monovanadate sites; while the isolated VOx are more selective to the olefin. The performance of various VOx catalysts is explained by the different chemical properties of the catalytic sites due to their structural differences.

Last modified

• 08/29/2018

Creator

• Hao Feng

DOI

• https://doi.org/10.21985/N2472X

Subject

• Chemistry

Keyword

• Physical Chemistry

Date created

• 2007-12-10

Resource type

• Dissertation

Rights statement

• In Copyright