The epoxidation of propylene with H-2-O-2 mixtures was studied over a gold catalyst supported on a Gemodified TS-1 catalyst at 170 degrees C. Shifts of X-ray diffraction lines to lower angle showed that the Ge was incorporated into the structure of the TS-1. The presence of Ge more than doubled the conversion from 1.6% to 4% while increasing selectivity from 87% to 91%. Density functional theory calculations indicated that the origin of the enhanced activity was a ligand effect of Ge on Ti, which lowered the activation energy for the critical epoxidation step. (C) 2009 Elsevier Inc. All rights reserved.