Characterization of Catalysts for Hydrodeoxygenation of Bio-oils using Phenol as a Model Compound

Due to the environmental considerations, depletion of fossil fuel reserves and fluctuating non-renewable fuel price, converting non-edible lignocellulosic biomass into renewable energy resources has gained significant importance. Phenol has been chosen as a model compound for catalytic screening because it is abundant in bio-oil composition and shows a high resistance to oxygen removal during hydrodeoxygenation (HDO) reactions. HDO of phenol produces chemicals that can be used as transportation fuels (Aromatics) or fuel additives. Theoretically, HDO of phenol has two distinct reduction pathways: direct deoxygenation (DDO) and hydrogenation (HYD). The previous results published by our group showed a precedent activity and selectivity towards DDO of phenol over Ru/TiO2 catalyst. They also revealed that the particle size of the Ru/TiO2 catalyst played an important role for determining the reaction pathways. For instance, nanoparticles of Ru (∼2 nm) supported on TiO2 leads to DDO pathway, in contrast, large particles (∼30 nm) leads to HYD pathway. In the current thesis, a systematic study was performed to determine the effects of a TiO2 support and noble metal (Ru) on the HDO of phenol and to determine the activity and selectivity of the catalyst towards the DDO pathway (Aromatics). Reactions were performed in batch and flow reactors at 300 °C. Evaluation of the catalysts using batch mode showed that the nanoparticles of ruthenium (∼2 nm) supported on titanium dioxide (TiO2) yield significant activity and selectivity for phenol HDO. The main product of this reaction was benzene. Furthermore, the activity and selectivity observed during the deoxygenation of phenol over the ruthenium catalyst were not stable. Therefore, a high-pressure burette along with a 25 mL Parr reactor were used to test the activity and stability of the Ru/TiO2 catalyst by calculating the hydrogen consumption rate as a function of pressure. During the reaction, the hydrogen consumption rate was decreased which gave an indication that the catalyst was deactivated with time. Subsequently, we have decided to use a packed flow reactor to study the activity, selectivity, and stability of the Ru/TiO2 catalyst during HDO of phenol. The packed bed reactor results showed that the HYD pathway is the dominant pathway which is not consistent with batch reactor results. It also showed that the catalyst was deactivated during time on stream (TOS). A newly synthesized catalyst of Ru/TiO2 (UMaine Catalyst) was used to test its activity and stability for phenol HDO. The data for the newly synthesized catalyst were consistent with previous data from our catalyst group. Both catalysts show that the activity of the Ru/TiO2 catalyst is not stable. Tetrahydrofuran (THF) solvent was then used in the flow reactor and showed better activity and selectivity towards DDO pathway compared with previous results of flow reactor