Abstract: To address the deactivation of Mn-based catalysts during the catalytic oxidation of formaldehyde at room temperature, a MnO_x/SFCCC catalyst was prepared via an in-situ growth method using spent fluid catalytic cracking catalyst （SFCCC） as the support. The causes of catalyst deactivation during continuous operation and the performance recovery after thermal regeneration at 50-250 °C were systematically investigated. Among the regeneration temperatures examined, the catalyst regenerated at 200 °C exhibited the best recovery performance, with its activity restored to 95% within 10 h. After four consecutive reaction–regeneration cycles, the formaldehyde removal efficiency still remained above 60%. BET and SEM results showed that the fresh catalyst possessed a specific surface area of 154 m²·g⁻¹ and a pore volume of 0.191 cm³·g⁻¹. After deactivation, small-particle agglomeration appeared on the catalyst surface, accompanied by a significant decrease in textural properties, with the specific surface area and pore volume dropping to 90 m²·g⁻¹ and 0.141 cm³·g⁻¹, respectively. After regeneration at 200 °C, these values recovered to 130 m²·g⁻¹ and 0.185 cm³·g⁻¹, respectively. XPS, O₂-TPD, and H₂-TPR analyses revealed that catalyst deactivation was associated with the reduction of Mn³⁺ species and the consumption of surface reducible oxygen species. FTIR, TPO, and TG further confirmed that the deactivation mainly resulted from the reversible coverage of active sites by carbon-containing intermediates, predominantly formate species, and that mild heating at 200 °C could effectively regenerate the catalyst.