Hydrodeoxygenation of Bio-Oil over Pt Supported Catalyst: Importance of Mesopores and Acidity

Biofuel shows promising potentials to answer our current globule challenges on energy and environment. The key to its success lies on the conversion of biomass to high quality biofuel and/or chemical feedstocks. But unlike fossil fuel, biofuel is composed of many carbohydrates with high oxygen content and low hydrogen/carbon ratios, which leads to the low heat capacity, poor thermal and chemical stability of biofuel. Further hydrogenation and deoxygenation must be done before biofuel can serve as attractive replacements of the conventional fuel. We hypothesize that catalyst supported mesoporous zeolites (i.e., hierarchical zeolites) could provide superior activity and selectivity than other common support materials (e.g., alumina and silica): zeolites offer strong acidity for hydrogenation and good hydrothermal stability while the hierarchical structure improves the diffusion of large compounds (presenting with a high percentage in bio-oil), the reduction of pore blocking, and/or the lessening of deactivation of catalyst from coking. To demonstrate our concept, a novel dual-template synthesis approach was used to produce new mesoporous ZSM-5 zeolites and Pt catalyst was impregnated for catalytic hydrodeoxygenation of bio-oil. We found better catalytic activity of mesoporous ZSM-5 zeolites based catalysts than their conventional counterparts (i.e., microporous zeolites) and those on alumina or silica in the deoxygenation or hydrogenation of phenol-type bio-oil compounds. By testing on three model bio-oil compounds, it showed that the catalysts with strong acidity (e.g. ZSM-5) have high hydrodeoxygantion activity while mesopores of support can further help improve the catalytical performance of ZSM-5. Exploring on new synthesis strategies for more desired hierarchical zeolites (e.g., with large mesopores, strong acidity, or their combinations) and/or better catalytic performance of these new hierarchical zeolites are currently under investigation. Our efforts are expected to help make biomass/biofuel a truly renewable and environmental friendly energy source.