Hydrodeoxygenation of bio-oil model compounds on supported noble metal catalysts

This thesis focuses on understanding acidic effects on the mechanisms of Pt or Pd-catalyzed bio-oil model ketone or aldehyde hydrodeoxygenation (HDO) and application of nanocatalysts - supported Pt and Pd with different surface acidity in the hydrodeoxygenation of acetophenone and benzaldehyde. The first part of the thesis addressed the understanding of bio-oil model ketone compound - acetophenone hydrodeoxygenation mechanism over alumina and silica-alumina supported Pt and Pd catalysts by in-situ attenuated total reflection infrared spectroscopy (ATR-IR) in combination with modulation excitation spectroscopy (MES) and phase sensitive detection (PSD). Experimental results indicated acidic supports promoted the hydrodeoxygenation of acetophenone (AP) to produce ethylbenzene (EB). Specially, on alumina supported Pt, AP was predominantly adsorbed on Pt via its η1 (O) configuration and this species was hydrogenated with high chemoselectivity to 1-phenylethanol (PE). On silica-alumina supported Pd, hydrodeoxygenation of AP to EB involves transformation of a carbonyl group to PE via η1 (O) configuration, followed by a dehydration producing styrene on acidic sites of supports, the styrene was further hydrogenated to EB on Pd. The second part focused on the application of acidic supports supported catalysts Pt/Al-MCM-41 and Pt/SiO2-Al2O3 on hydrodeoxygenation of acetophenone and benzaldehyde. Results indicated that Pt/Al-MCM-41 catalysts serve as bifunctional catalysts in the hydrogenation of AP. The overall activity over the noble metal catalysts on acidic supports MCM-41 increased with the increase of surface acidity up to support Si/Al=20, further increase the surface acidity leads to the decrease of catalytic activity. The increase of surface acidity up to Si/Al=20 also promotes the hydrogenation of aromatic ring to produce CMK and CE. For hydrodeoxygenation of benzaldehyde, products toward hydrogenation of both carbonyl and aromatic ring can be produced on a reference Pt/Al2O3 catalyst at 80°C whereas when temperature was increased to 200°C, only toluene and benzene can be detected. SiO2-doped Pt/SiO2-Al2O3 catalysts showed 10%-20% higher catalytic activity than reference catalyst of Pt/Al2O3 under similar reaction condition. Acidity did also influence catalytic selectivity of benzaldehyde hydrodeoxygenation, toluene prefers to form on relative low acidic catalysts whereas methylcyclohexane was more easily formed on high acidic catalysts.