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A series of Ce-M(Cu, Co and Fe) catalysts were synthesized via sol–gel methods. In situ DRIFTS was introduced to explored the process of toluene degradation, confirming oxygen vacancies played an important role. [Display omitted] • Ce-Cu sample exhibited best catalytic activity and stability for toluene oxidation. • Superb activity was attributed to high Ce3+/ Ce4+ and high O ads /O latt. • The oxygen vacancies were modulated by different metal doping. • Benzoic acid was key intermediates in toluene catalysis by in situ DRIFT analysis. A series of CeO 2 samples modified with various metals M (M = Cu, Co and Fe) were synthesized via a simple sol–gel approach. The experimental results showed that there were significant differences in the catalytic activities between different metal-doped Ce-based catalysts. The Ce-Cu sample possessed excellent catalytic activity at low temperatures, and 90 % conversion of toluene was at 255 ℃, which was due to the presence of ample oxygen vacancies (O v). Three degradation pathways for toluene oxidation were inferred based on the in situ DRIFTS. The Ce-Cu catalysts possessed abundant O v , which improved the conversion between O ads → O latt and the breakage of aromatic rings, thus reducing the production of intermediates. The Ce-Co and Ce-Fe catalysts owned few amounts of O v species, leading to an extensive amount of by-products. Furthermore, the loss of active sites inhibited the reaction rate, causing the inferior catalytic performance of the Ce-Co and Ce-Fe samples. [ABSTRACT FROM AUTHOR]