Low-temperature catalysts of mesoporous Co3O4 and AU/Co3O4 with high catalytic activities for the trace ethylene oxidation at 0 degrees C are reported in this paper. The catalysts were prepared by using the nanocasting method, and the mesostructure was replicated from three-dimensional (3D) cubic KIT-6 silicas. High resolution transmission electron microscopy (HRTEM) studies revealed that {110} facets were the exposed active surfaces in the mesoporous Co3O4, whereas the Co3O4 nanosheets prepared by the precipitation method exhibited the most exposed {112} facets. We found that the mesoporous Co3O4 was significantly more active for ethylene oxidation than the Co3O4 nanosheets. The results indicated that the crystal facet {110} of Co3O4 played an essential role in determining its catalytic oxidation performance. The synthesized Au/Co3O4 materials, in which the gold nanoparticles were assembled into the pore walls of the Co3O4 mesoporous support, exhibited stable, highly dispersed, and exposed gold sites. Gold nanoparticles present on Co3O4 readily produced surface-active oxygen species and promoted ethylene oxidation to achieve a 76% conversion at 0 degrees C, which is the highest conversion reported yet.