Discovering the key role of MnO2 and CeO2 particles in the Fe2O3 catalysts for enhancing the catalytic oxidation of VOC: Synergistic effect of the lattice oxygen species and surface-adsorbed oxygen.

ABSTRACT

Highly active mesoporous Fe-Mn-Ce catalysts with high specific surface area (SBET) were synthesized by a modified precipitation process for catalyzing toluene oxidation. The Fe0.85Mn0.1Ce0.05 catalyst presents richer surface oxygen species (OS), a higher proportion of Mn4+ and Ce4+, a higher concentration of lattice defects and oxygen vacancies, the highest Oads/Olatt ratio, and a superior low-temperature redox property compared with the Fe-Mn binary oxide and Fe2O3 and MnO2 catalysts. The properties contribute to a high catalytic activity to achieve T90% of toluene conversion at 264 °C and 185 °C with a gas hourly space velocity (GHSV) at 180,000 and 20,000 mL/(g∙h), respectively. The introduction of a slight quantity of Ce and Mn onto the Fe2O3 catalyst is the key to enhancing the synergistic effect of the lattice OS and surface-adsorbed oxygen, contributing to the activation oxidation procedure of toluene. In-situ DRIFTS analysis reveals that the rich oxygen vacancy concentration of catalysts accelerates the key steps for the generation and activation of oxidized products. These catalysts with rich oxygen vacancies can efficiently diminish the accumulation of a small number of the intermediary species (phenolate, C6H5-OH) produced during the catalytic oxidation of toluene.