Discipline: Technology and Engineering
Subcategory: Chemistry (not Biochemistry)
Kindle Williams - University of Alabama
Co-Author(s): Madelyn Ball, Canan Sener, Yifei Liu, and James Dumesic, University of Wisconsin, Madison, WI
The generation of fuels, such as ethanol, from biomass is a promising source of renewable energy. Bimetallic catalysts are a relatively new subject of study that may help to further the technology of sustainable biofuels. It has been shown that rhodium, which is an effective catalyst for higher alcohol synthesis, exhibits enhanced selectivity to C2 oxygenated species (i.e., ethanol and acetaldehyde) when augmented with Mn. It was hypothesized that this enhancement can be attributed to Rh and Mn forming a bimetallic structure that is conducive to higher alcohol synthesis from a mixture of hydrogen and carbon monoxide (i.e., syngas). Chemisorption can be utilized to elucidate the nature of this bimetallic structure. Previous work in the Dumesic group has improved the synthesis of supported Rh/Mn catalysts, so it was our task to characterize these materials in greater depth. Our objectives were to identify a molecule suitable for independently probing Rh and Mn through chemisorption and to determine optimal conditions for probe adsorption. Our studies were initiated by synthesizing catalysts through incipient wetness impregnation, then calcining and reducing them before conducting chemisorption experiments. CO is a well-established probe of Rh active sites, so the focus of the research was primarily to probe Mn sites. A variety of adsorbents were dosed onto the catalysts in a range of temperatures. Most notably, experimental data were gathered for N2O, CO2, and CO chemisorption. Nitrous oxide was deemed a poor probe because of its low uptake on Mn and ability to displace CO on CO-covered Rh. Likewise, it was found that carbon dioxide adsorbs too strongly to the silica catalyst support, and thus it is also an inappropriate probe. Carbon monoxide seems to be the most promising probe for the Rh/Mn bimetallic system, but only at temperatures around -80 ˚C due to the energetics of the system. Future work will involve the use of IR spectroscopy to observe the relative uptake of CO on Rh and Mn by analyzing peak intensities. In addition, adsorbents such as NO may be the subject of further investigations.
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Funder Acknowledgement(s): Thanks to the University of Wisconsin-Madison Graduate School and National Science Foundation through the UW-Madison Materials Research Science and Engineering Center (DMR-0520527) and Nanoscale Science and Engineering Center (DMR-0425880).
Faculty Advisor: James Dumesic, email@example.com