Influence of Rare-Earth Promoters (Ce, Zr and La) on Catalytic Performance of Copper-Based Catalyst in Toluene Oxidation

Copper-infused mixed metal oxides have been identified as powerful catalysts for eliminating volatile organic compounds (VOCs) due to their widespread availability and cost-effectiveness. The copper metal oxide catalysts were synthesized using the sol-gel method and promoted with rare earth elements, La, Ce, and Zr, to catalyze the oxidation of toluene. Compared to all tested catalysts, CuLaOx demonstrates the least activity igniting activity even though La appears to enhance copper dispersion and generate a large number of oxygen species on the surface. CuZrOx displays remarkable thermal stability, resulting in a minimal amount of lattice oxygen participating in toluene oxidation. The introduction of Ce into the CuCeOx catalyst enhances its activity significantly, attributed to the exceptional reducibility of copper species. Therefore, the TOF for the CuCeOx, CuLaOx and CuZrOx catalysts are 9.23–24.8 × 10−3 s−1, 1.29–6.22 × 10−3 s−1, and 1.05–10.03 × 10−3 s−1 at 200–400 °C, respectively. The infrared spectra, observed at varying temperatures during toluene oxidation, were presented. Interestingly, all catalysts demonstrated a comparable reaction pathway. The catalytic oxidation mechanism is expected to proceed via the intermediates of toluene-alkoxide-aldehydic-carboxylic acid, ultimately culminating in complete degradation to CO2 and H2O. This study establishes a theoretical foundation for the judicious selection of suitable rare earth elements as promoters, enabling the development of copper-based catalysts for efficient volatile organic compound (VOC) removal in industrial settings.