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Catalytic oxidation is a promising approach to eliminating formaldehyde (HCHO) to improve indoor air quality. Herein, CeO 2 was explored due to its remarkable properties for oxygen storage and oxygen transfer capability for co-doping δ-MnO 2 alongside cobalt for enhanced low-temperature oxidation of HCHO. Various characterization techniques were deployed to understand the morphology and physicochemical properties of the synthesized catalysts. The Co-Ce co-doped catalysts with low CeO 2 loading (0.05 and 0.1) showed higher catalytic activity for HCHO oxidation due to their higher concentration of surface-active oxygen species. Catalytic oxidation results showed that the presence of CeO 2 leads to the generation of methanol as a secondary hazardous pollutant. Methanol selectivity increases with increasing CeO 2 loading in the catalysts. The results from in-situ DRIFTS confirmed the formation of methoxy species in the presence of CeO 2 , which are intermediates for methanol generation. Considering the recent interest in CeO 2 as a potential catalyst for practical abatement of HCHO from the indoor environment, this work has thus raised questions on the safety of using CeO 2 as a catalytic material for HCHO oxidation. It also provides insights into the surface reaction mechanism leading to the generation of methanol in the presence of CeO 2. [Display omitted] • Bimetallic co-doping of δ MnO 2 with Ce and Co does not enhance HCHO oxidation. • High CeO 2 doping results in the structural collapse and lower catalytic activity. • CeO 2 leads to the generation of methanol during the catalytic oxidation. • Cannizzaro disproportionation reaction is proposed for methanol generation. [ABSTRACT FROM AUTHOR]