We exploit interfacial charge transfer from titania (TiO2) to copper (Cu) to design catalytic Cu/TiO2 composite aerogels that shift the chemical state of Cu nanoparticles away from Cu2+, making them highly active for low temperature CO oxidation. The high degree of interfacial contact between similar to 2-3 nm diameter Cu particles and the networked similar to 10 nm-diameter TiO2 particles in ultraporous aerogel stabilizes a high ratio of Cu0/1+:Cu2+. The reduced nature of Cu in Cu/TiO2 aerogels is evidenced by a strong surface plasmon resonance in its diffuse reflectance UV-vis spectrum, by its X-ray photoelectron spectral features, and by infrared spectroscopic evidence of CO binding at the catalyst surface. In contrast, when larger diameter (similar to 50-60 nm), non networked TiO2 particles are used to support Cu nanoparticles, the single planar nanoscale interface between Cu and the support particle stabilizes a much lower fraction of low-valent Cu. The Cu0/1+ speciation stabilized within the aerogel catalyzes low-temperature CO oxidation (< 100 degrees C) at high conversion rates and does not necessitate high temperature activation in a reducing gas stream-performance that the non-networked catalyst cannot meet. Our work demonstrates how nanoscale interfacial materials design can be exploited to create active Cu nanoparticle based catalysts that are stable under practical conditions.