Low-temperature CO oxidation over Cu/Pt co-doped ZrO₂ nanoparticles synthesized by solution combustion

Zirconia (ZrO₂) nanoparticles co-doped with Cu and Pt were applied as catalysts for carbon monoxide (CO) oxidation. These materials were prepared through solution combustion in order to obtain highly active and stable catalytic nanomaterials. This method allows Pt²⁺ and Cu²⁺ ions to dissolve into the ZrO₂ lattice and thus creates oxygen vacancies due to lattice distortion and charge imbalance. High-resolution transmission electron microscopy (HRTEM) results showed Cu/Pt co-doped ZrO₂ nanoparticles with a size of ca. 10 nm. X-ray diffraction (XRD) and Raman spectra confirmed cubic structure and larger oxygen vacancies. The nanoparticles showed excellent activity for CO oxidation. The temperature T₅₀ (the temperature at which 50% of CO are converted) was lowered by 175 °C in comparison to bare ZrO₂. Further, they exhibited very high stability for CO reaction (time-on-stream ≈ 70 h). This is due to combined effect of smaller particle size, large oxygen vacancies, high specific surface area and better thermal stability of the Cu/Pt co-doped ZrO₂ nanoparticles. The apparent activation energy for CO oxidation is found to be 45.6 kJ·mol^-1. The CO conversion decreases with increase in gas hourly space velocity (GHSV) and initial CO concentration.