Low-temperature CO oxidation at persistent low-valent Cu nanoparticles on TiO₂ aerogels

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 ∼2–3 nm–diameter Cu particles and the networked ∼10 nm–diameter TiO₂ particles in ultraporous aerogel stabilizes a high ratio of Cu^0/1+: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 (∼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 Cu^0/1+ speciation stabilized within the aerogel catalyzes low-temperature CO oxidation (<100 °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.