Date of Award

Fall 11-17-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Chester Wilson

Abstract

The U.S. produces 5559.6 million metric tons of carbon dioxide annually, of which 21% is produced by industrial processes. Steam reforming, an industrial process that accounts for 95% of all hydrogen production in industry, produces 134.5 million metric tons of carbon dioxide or around 11% of the total carbon dioxide produced by industry. This carbon dioxide is then either emitted or goes through a sequestration process that accounts for 75% of the plant's operational costs. An alternative reaction to steam reforming is dry reforming, which utilizes carbon dioxide rather than emitting it and can be used in conjunction with current steam reforming to remove costs associated with sequestration. Dry reforming is not used in industry due to its higher energy requirements and lower catalyst life due to carbon deposition. To reduce energy requirements and extend the life of the dry reforming catalyst, nanostructured heterogenous metals and ceramics made from an electrospinning process and graphene nanoscrolls made through a bulk electrochemical method are proposed as a catalyst and highly sensitive chemiresistive sensors to monitor precise gas quantities within the reaction without the need for extra energy supplied to them.

This dissertation explores the use of nanostructured heterogeneous metals and nonmetals as more resilient catalysts and supports for the dry reforming technique. To reduce the energy required for dry reforming, catalysts were fabricated through an electrospinning process and used nickel as the primary catalyst due to its high activity and low cost. Iron was used within the nanofibers to create a redox side reaction to decrease the solid carbon formation on the surface of the catalysts showing higher reactivity after 15 hours of reaction. Electrospun magnesium aluminate spinels ceramics were studied as a support and found to have excellent stability and reactivity, achieving an 83% lower apparent activation energy than nickel catalysts alone. To reduce coking on the surface of the catalyst, graphene nanoscrolls were fabricated using a scalable electrochemical exfoliation technique and used as supports in the dry reforming reaction to nickel nanoparticles. They were found to have similar properties to carbon nanotube supports reported in previous literature and a 30% lower coking amount than traditional nickel catalysts after 15 hours and 12% lower apparent activation energy than traditional nickel catalysts. Finally, to be able to precisely monitor gas evolution, the electrospun metal nanofibers and graphene nanoscrolls were used as sensing elements in a polyaniline doped gas sensor. These sensors were tested at room temperature with methane, ethanol gas and acetone gas and found to have responses over 100% higher than polyaniline alone. Combined, catalytic nanofibers and graphene nanoscroll supports have been shown to lower the apparent activation energy requirements and resist carbon deposition induced deactivation on the catalyst while allowing for a passive sensing material, offering a pathway forward towards an economically viable dry reforming process.

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