The authors present results of an investigation into the dispersion Of MoO3 on TiO2SiO2 composite and its reactivity in transesterification of dimethyl oxalate (DMO) with phenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). They examined the effects of support composition, MoO3 content, and reaction time on activities of the transesterification. The results show that MoO3/TiO0-SiO2 is more active and selective than MoO3/TiO2, MoO3/SiO2, and TiO2SiO2 catalysts in the transesterification reaction. The best catalytic performance is obtained over a 12%MoO3/8%TiO2SiO2, providing a 71.8% DMO conversion and 59.0%, 40.1% selectivities for MPO and DPO, respectively. Through employing X-ray diffraction and inductively coupled plasma-optic emission spectrometry, they show evidence strongly suggesting that improvement of catalytic reactivity over the TiO2-modified SiO2 support can be ascribed to the enhanced metal oxide support interactions and the increased dispersion capacity Of MoO3 phase. They also present evidence showing that incorporation of TiO2 in SiO2 can elevate the monolayer dispersion capacity Of MoO3 on SiO2. Thus, they conclude that increased DPO selectivity from MoO3/TiO0-SiO2 catalysts can be primarily attributed to the improvement Of MoO3 dispersion and the synergistic effect between amorphous MoO3 and amorphous TiO2. (c) 2008 American Institute of Chemical Engineers.