Transesterification of dimethyl oxalate with phenol over TiO 2 /SiO 2 : Catalyst screening and reaction optimization

Physicochemical properties of silica‐supported titanium oxide catalysts as well as their performances for transesterification of dimethyl oxalate (DMO) with phenol to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) have been investigated systematically. Various wt % of TiO 2 were loaded on SiO 2 by a two‐step wet impregnation method. The surface properties of TiO 2 /SiO 2 catalysts were explored by various characterization techniques (BET, SEM, ICP, XPS, XRD, FTIR of pyridine adsorption, and NH 3 ‐TPD). Catalytic performances of TiO 2 /SiO 2 catalysts were found to be strongly dependent on TiO 2 dispersion and surface acidity. Monolayer dispersion capacity of TiO 2 on silica was estimated to be about 4.0 TiO 2 molecules per nm 2 (SiO 2 ) and no crystalline TiO 2 was detected at TiO 2 loading less than 12 wt %. FTIR and TPD analysis suggested that weak Lewis acid sites on the surface of TiO 2 /SiO 2 were responsible for their unique selectivity to the target products, MPO and DPO. An optimization of reaction conditions for the transesterification of DMO with phenol was performed over 12 wt % TiO 2 /SiO 2 calcined at 550°C. In addition, we studied the disproportionation reaction from MPO to DPO via a catalytic distillation process, which is highly efficient to promote formation of the desired DPO. © 2008 American Institute of Chemical Engineers AIChE J, 2008