Trevor Seegmiller and Dr. Calvin Bartholomew, Department of Chemical Engineering
Fischer-Tropsch synthesis (FTS) is the process for converting syngas (carbon monoxide and hydrogen) into liquid fuels such as gasoline and diesel. A cobalt or iron catalyst is required for the process. Cobalt catalysts have the highest effectiveness and stability in FTS; however, they are more expensive due to higher materials cost as well as the time-consuming and complex processes generally associated with manufacture.
Cobalt Fischer-Tropsch (FT) catalyst manufacture was developed successfully eight decades ago. Although significant refinements have been made, the process is still long and time consuming. Simplifying manufacture would lower costs of cobalt catalyst, allowing FTS to be used to produce liquid fuels from biomass or other organic sources.
During the last six years, Dr. Woodfield’s nanotech group in the BYU Chemistry Department has researched simple, 1-pot preparation methods for producing uniformly-sized metal oxide nanoparticles. The purpose of this project was to determine if the 1-pot preparation techniques could produce suitable catalyst candidates for FTS. It is possible that by using these preparation techniques for cobalt FT catalysts, the manufacture process could be shortened from days to hours.
To determine the activity and selectivity of a catalyst, testing at FTS conditions is required. Because these tests are resource intensive, few catalysts can be tested for activity and selectivity measurements. Preliminary tests, such as surface area and pore structure measurements, screen candidates for full testing.
Generally, the larger the catalyst surface area, the more active the catalyst is. FTS requires catalysts to have surface areas greater than 150 m2/g and pores greater than 10 nm. Catalysts found outside these requirements are not tested at FTS conditions.
Three major series of samples were manufactured over the course of the project. The first sample series used previously prepared alumina (aluminum oxide) supports. The cobalt catalyst was precipitated from cobalt chemical precursors in the presence of these aluminum supports. The second series of the 1-pot method involves cobalt and alumina precipitated simultaneously from chemical precursors. The third series of the cobalt catalyst preparation method changed the chemical used as the alumina precursor.
In the first iteration, cobalt was precipitated onto a premade alumina support. Two samples were prepared of this iteration, and poor surface area measurements resulted. Because of poor surface area measurements, further investigation of this preparation method was halted. It was also hypothesized that precipitated cobalt particles did not uniformly permeate the alumina support, and confirmation is pending.
The next stage of research involved precipitating cobalt and alumina particles simultaneously. Of the six samples prepared, the two most promising candidates obtained surface areas near 250 m2/g. Although the surface areas were optimal for FTS, the pore diameter of 2 nm prevented further investigation.
The current stage of research is using a different chemical precursor to precipitate alumina particles. Additional liquid was added to aid the reaction. Three liquids were selected: pure water, pure isopropyl alcohol, and 50/50 isopropyl alcohol/water mixture. Six preparations were made, and the most promising sample has a surface area 172 m2/g and a pore diameter of 17 nm. Surprisingly, the catalyst preparation did not require the precipitating agent.
The next set of steps is testing the extent of reduction of the catalyst. In FTS, the reduced metal is used as the catalyst of the reaction. The optimal catalyst will completely reduce so that there are no metal oxides present in the catalyst. The catalyst had a preliminary extent of reduction of 78%. Further testing of this sample may include testing at FTS conditions and results are anticipated be published in a reputable journal (such as the Journal of Catalysis) by the end of the academic year.
At the beginning of the project, I had expectations of what constituted research. I thought an experiment was conducted, results were found, and then a report was written. I was surprised by how quickly research could be conducted. My original plan and schedule was very optimistic; however, delays due to malfunctions and maintenance slowed the pace. I have found that research is just as much caring for equipment as it is conducting experiments.
Although some aspects of the project have been very successful, I did not anticipate how many unsuccessful experiments occurred. While conducting research, I have also learned the importance of interpreting data correctly and that failures are just as informative as successes.
I have also learned that guidance from a mentor is very helpful when conducting research. A mentor has the experience and knowledge to channel the direction of the researcher so that less time is wasted on experiments that will not tell very useful information.
The project will continue by conducting further research on the sample. This will include evidence of a unique anomaly consistent with this preparation method. The project is expected to be completed at the conclusion of this academic school year with a publication submitted to the Journal of Catalysis.