Modulate synthesis of CeMn solid solution using various alcohols for toluene catalytic oxidation: synergistic effect of Ce-Mn and reaction mechanism.

A redox co-precipitation method was employed to synthesize CeMn homogeneous solid solutions, utilizing various alcohols as activating agents. Ethanol effectively orchestrated the precipitation of CeO and MnO, promoting their co-growth. As a result, the CeMn-EA achieved 90 % toluene conversion at 218 ℃ (T =218 ℃) with a weight hourly space velocity (WHSV) of 48000 ml/(g·h). It also demonstrated high adaptability to increased WHSV, suggesting its potential for industrial-scale applications. The uniform dispersion of Ce and Mn accelerated the coupling between Ce/Ce and Mn/Mn, engineering numerous oxygen vacancies, which enhanced the activation of gas-phase oxygen and the mobility of lattice oxygen. In situ DRIFTS confirmed that toluene oxidation accommodated both Langmuir-Hinshelwood (L-H) and Mars-van Krevelen (MvK) mechanisms, with benzoate identified as a pivotal intermediate. Enhanced oxygen mobility facilitated the cleavage of the benzene ring, which was the rate-determining step. Additionally, the introduction of HO significantly enhanced the dissociation and adsorption of toluene and facilitated the activation of gas-phase oxygen. At higher temperatures, HO could further activate lattice oxygen engaging in toluene oxidation. ENVIRONMENTAL IMPLICATION: Volatile organic compounds (VOCs) have emerged as major air pollutants due to the changes in air pollution patterns. They can act as precursors to near-surface ozone and haze. Toluene, a typical VOC, is primarily released from anthropogenic sources and poses significant risks to human health and the environment. Ce-based catalysts have been demonstrated efficiency in toluene oxidation due to their excellent oxygen storage and release properties. This study synthesized CeMn homogeneous solid solutions utilizing various alcohols as activating agents, which possessed abundant oxygen vacancies and optimum oxygen activation capacity to oxidize toluene in time.