Bio-oil derived from lignocellulosic biomass contains phenols and its derivatives. Lignocellulosic bio-oil is an emerging source of useful chemicals and fuels. In this research, phenol is used as a model molecule to represent lignin bio-oil. Hydrogenation of phenol yields cyclohexanone and cyclohexanol. Selective phenol hydrogenation to cyclohexanone is of particular interest as at higher catalytic activity, further hydrogenation of cyclohexanone can lead to cyclohexanol formation and low cyclohexanone yield. The presence of basic sites on the support has shown to enhance the catalytic activity of phenol hydrogenation and its selectivity to cyclohexanone by improving adsorption of phenol and metal-support interaction. We have developed a palladium (Pd) catalysts for aqueous phase hydrogenation of phenol using an organic-inorganic hybrid (OIH) silica support modified by incorporation of basic amine sites. The organosilica support is synthesized using a sol gel method from an aromatic organometallic precursor, bis (trimethoxy silyl ethyl) benzene (BTEB). The presence of organics in the support renders it hydrophobicity and selective affinity towards organic reactant. This enhances the local concentration of the reactant near the active sites, hence, promoting the reaction kinetics.
The basic sites were incorporated using bis[(3-trimethoxysilyl)propyl]amine (BTMSPA) as a co-precursor along with BTEB. The reactions were performed in a 300 ml batch reactor at 150oC and 50 bar H2 pressure. Organo-silica supported catalyst showed significantly better conversion than conventional mesoporous inorganic silica. Pd catalysts and the supports were characterized by N2 physisorption, infrared Spectroscopy, nuclear magnetic resonance spectroscopy, transmission electron microscopy (TEM), equilibrium adsorption experiments, X-ray photoelectron spectrometry. The effect of different methods of incorporating basic sites, one-pot synthesis and grafting is also studied.
The current work showed that BTEB based hybrid material can be an excellent support for upgrading the aromatics of the bio-oil to valuable chemicals.
