Master of Engineering Science
Chemical and Biochemical Engineering
Catalytic hydrodeoxygenation (HDO) is a process for upgrading crude bio-oil as it has a high oxygen content which causes several undesirable properties. Current methods for HDO use sulfided NiMo and CoMo or supported noble metal catalysts which hydrogenate aromatic rings, leading to less valuable products and increasing the hydrogen consumption. Using 10 wt. % MoO3 supported on ZrO2, TiO2, γ-Al2O3, SiO2 and CeO2, we investigated the atmospheric HDO of anisole, a model compound, at 350 °C. All catalysts achieved C – O bond cleavage, preserving the aromatic ring. In situ UV-Vis spectroscopy showed a peak corresponding to intervalence charge transfer (IVCT) transitions where Mo5+ – O – Mo6+ → Mo6+ – O – Mo5+. The IVCT positions were used to classify the catalysts according to their degree of reduction. In general, a direct correlation is established between the supported catalyst’s activity and its ability to preserve Mo5+ sites, preventing over-reduction to less active Mo4+ sites.
Summary for Lay Audience
Currently, the world’s primary source of transportation fuel is fossil fuels, which contribute to climate change and are a non-renewable source of energy. Bio-oil, a renewable source of energy derived from biomass, such as wood and switchgrass, is considered a promising alternative source of energy. However, the problem is that it contains a high concentration of oxygen, leading to undesirable characteristics, such as high acidity. Therefore, oxygen must be removed for it to be considered a feasible source of energy. One method for achieving this is hydrodeoxygenation (HDO), where hydrogen (H2) removes oxygen in the form of H2O. HDO studies have been successfully carried out using different types of catalysts. However, with these catalysts, hydrogen not only reacts to break the carbon-oxygen bond, but also reacts to break the carbon double bonds to single bonds. This results in high levels of hydrogen consumption and lower value products. However, recently molybdenum oxide (MoO3) on a support has been shown to be an effective catalyst for HDO, where hydrogen does not react with the carbon double bonds.
In this work, we investigated the impact of a support (ZrO2, TiO2, γ-Al2O3 and SiO2) on the HDO activity using MoO3. The ZrO2 and TiO2 supported catalysts had significantly higher degrees of HDO relative to the other catalysts and were the most stable. Although HDO using the γ-Al2O3 supported catalyst initially resulted in the highest levels of carbon-oxygen bond breaking, it did not break the specific carbon-oxygen bond needed to remove the oxygen and it deactivated quickly. Generally, we found that the activity of the catalyst was correlated with its ability to preserve a certain number of oxygen vacancies per Mo atom. If too many oxygen vacancies were created, then MoO3 went to MoO2 which is not active for HDO. The oxygen vacancies were the easiest to create on the ZrO2 and TiO2 supported catalysts but the γ-Al2O3 supported catalyst was able to prevent too many oxygen vacancies from being created. When the catalysts were synthesized, MoO3 was the most dispersed on the γ-Al2O3 catalyst but post-reaction it was the least dispersed.
Walker, Chantal, "The Effect of MoOx Reducibility on its Activity for Anisole Hydrodeoxygenation" (2020). Electronic Thesis and Dissertation Repository. 7525.