Bridged polysilsesquioxanes are highly versatile silica-based organic-inorganic hybrid (OIH) materials derived from precursors consisting of an organic bridging group and at least two trifunctional silyl groups. Chemical and textural properties of the material can be modified by appropriate choice of precursor. This offers a great scope for synthesizing catalyst scaffolds with tailored morphologies and functionalities suitable for a particular reaction. In this research, we have used bis (trimethoxysilyl ethyl) benzene (BTEB) as a precursor to synthesize the OIH material. The hybrid material has an aromatic ring which can interact with the aromatic molecules via π- π stacking and hence can be used to selectively adsorb aromatics.
Bio-oil derived from lignocellulosic biomass contains phenols and its derivatives. Lignocellulosic bio-oil is an emerging source of useful chemicals and fuels. Owing to the affinity of the BTEB based hybrid material to aromatics, it can be an excellent support for upgrading the aromatics of the bio-oil to valuable chemicals. In this research, phenol is used as a model molecule to represent lignin bio-oil. BTEB-based hybrid material is used as a support for a palladium (Pd) catalyst in aqueous phase hydrogenation of phenol to cyclohexanol and cyclohexanone. These chemicals are used as solvents and as starting materials for manufacturing nylon and esters. The reactions were performed in a 300 ml autoclave batch reactor at 150^oC-200^oC and 50 bar H₂ pressure. The activity of BTEB based organo-silica supported was compared with conventional mesoporous inorganic silica. BTEB based organo-silica supported catalysts showed significantly better conversion. The effect of aromatic content and the hydrophobicity of the support on the activity of the catalyst was explored in the study. Bis (trimethoxy silyl) ethane was used to change the aromatic content of the support and the hydrophobicity of the support was changed by capping the hydrophilic -Si-OH groups with hydrophobic -Si-(CH₃)₃ groups. The effect of incorporating amine functionalized precursors, bis[3-trimethoxysilyl) propyl] amine and aminopropyl trimethoxy silane was also investigated. Pd catalysts and the supports were characterized by N₂ physisorption, IR and NMR Spectroscopy, thermogravimetry analysis, and equilibrium adsorption experiments.

Paul Edmiston

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