(521g) Selective Hydrogenation of Phenol in Aqueous Phase over Organically Modified Silica Support: Effect of Basic Site Incorporation

Phenol is one of the important platform chemicals used to produce valuable chemicals and intermediates such as cyclohexanone and cyclohexanol. These chemicals are used as solvents and as starting materials for manufacturing nylon and esters. Production of cyclohexanone and cyclohexanol from biomass derived phenol is a promising alternative to conventional route that uses petroleum-derived benzene and is limited by formation of undesired byproducts and low yield for cyclohexanone. 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 improve the catalytic activity of phenol hydrogenation and its selectivity to cyclohexanone. Thus, in this research we have developed palladium (Pd) catalysts for aqueous phase hydrogenation of phenol using an organic-inorganic hybrid (OIH) silica support modified by incorporation of basic sites. The organic silica support is synthesized using a sol gel method from a organometallic precursor, bis (trimethoxy silyl ethyl) benzene. This material offers a substantial advantage in incorporating functional entities on the catalyst support with simple modifications in the synthesis process. The basic sites were incorporated using bis[(3-trimethoxysilyl)propyl]amine (BTMSPA) as a co-precursor along with BTEB. Incorporating basic sites on the support showed increased selectivity to cyclohexanone because of its effect on adsorption of phenol, desorption of cyclohexanone and metal-support interaction. The effect of different methods of incorporating basic sites, during the support synthesis and post synthesis, was also studied. Pd catalysts and the supports were characterized by N₂ physisorption, Infrared Spectroscopy, Temperature programmed desorption, pulse CO chemisorption, transmission Electron Microscopy (TEM), equilibrium adsorption experiments, elemental analysis and inductively coupled plasma optical emission spectrometry.