Date of Award
Open Access Dissertation
An important step in the upgrading of biomass derived chemicals is the removal of excess oxygen. The works reported here are focused on studying the heterogeneous catalysts that can be utilized for that upgrading through hydrodeoxygenation. This work begins with a discussion of the alkylation of short chain platform chemicals for chain growth and also demonstrates the proof of concept of combining alkylation and hydrodeoxygenation in a single step. Then, because of the promising nature of ReOx- Pd/CeO2 for selective hydrodeoxygenation, a detailed study of ReOx/CeO2 is presented. Finally, a new surface structure interpretation is presented for P/Ni(111) which could be used for understanding Ni2P, a catalyst used for hydrodeoxygenation.
First, the production of long-chain hydrocarbons (C8+) from 2-methylfuran(2MF) and butanal in a single step reactive process is demonstrated by utilizing a bi-functional catalyst with both acid and metallic sites. A solid acid, Al-MCM-41, is utilized for the alkylation function and as a support for the transition metal, Pt. The Pt/Al-MCM-41 catalyst showed 96% yield for C8+ hydrocarbons, and the catalytic performance was stable over four reaction cycles of 20 hours each. The oligomerization of 2MF is also studied over solid catalysts. An aluminosilicate catalyst with Si/Al=20 is developed that demonstrates 40% conversion of 2MF in a pressurized batch reactor. This produces a mix of carbohydrates with the major components being the 2MF trimer and tetramer. Both the tetramer and the trimer are known to perform well under hydrodeoxygenation to form C15 and C20 hydrocarbons.
Second, to lead towards an explanation of the unique catalytic activity of ReOx- Pd/CeO2 for simultaneous hydrodeoxygenation of vicinal OH groups, the structure of ReOx/CeO2 is compared to the structure of ReOx on other oxides. Though the ReOx surface structure has been well characterized on SiO2, Al2O3, ZrO2 and TiO2 supports, the ReOx surface structure on CeO2 has not been rigorously studied. Several catalytic characterization techniques for structural determination are employed. It has been discovered that the structure of ReOx supported on CeO2 is unlike any previously studied supported ReOx. One of the main differences is that ReOx is chemisorbed on the surface of CeO2 in ambient conditions instead of being hydrolyzed by surface water. Additionally, instead of vaporizing as is commonly reported, it is shown that with high loadings of ReOx, crystalline Re2O7 is formed and remains on the surface even after calcination at 500oC. When ReOx is supported on an oxide, crystalline Re2O7 has never before been reported. It is shown that with the lowest loadings studied, 0.5wt%Re, Re has a +VII oxidation state, and ReOx is present with both tetrahedral and octahedral coordination. Using an 18O2 isotope exchange, it is shown that the tetrahedrally coordinated portion of ReOx/CeO2 has a single terminal oxygen. Upon reduction with H2, the octahedrally coordinated portion of ReOx reduces at a lower temperature than the tetrahedrally coordinated portion.
Lastly, a surface science study using LEED interpretation of phosphorous dosed on a Ni(111) single crystal is presented. A phase diagram of the surface P adsorbed on Ni(111) is developed showing distinct overlayer structures based on loading and annealing temperature. At low coverage, amorphous P was observed. At annealing temperatures below 400oC and coverages above 0.1 ML, a √7ˣ√7R19.1 structure was observed. Above 400oC, another complex structure was created. These structures seemed to correlate with each other and the √7ˣ√7R19.1 structure of P adsorbed on Ni(111) is therefore reinterpreted to have a rectangular unit cell. The new rectangular structure is discussed in relation to the Ni2P local structure.
Barrow, E.(2019). Heterogeneous Catalysis for the Upgrading of Biomass Derived Chemicals via Hydrodeoxygenation. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/5294