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The low conversion rate of coke during online coke cleaning is due to the stable structure of graphite carbon, which makes it difficult to react with steam. Therefore, there is an urgent need to design a catalyst for catalytic graphite carbon conversion to achieve efficient in situ coke cleaning. Alkaline earth metal Sr modified La-Fe based perovskite LSF- x (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were prepared by hydrothermal method. DFT and experimental results indicate that doping Sr at the A-site reduces the adsorption energy barrier of water molecules, promotes the decomposition of water molecules to produce absorbed and free hydroxyl radicals, and thereby enhances the conversion of graphite carbon. At 900 °C, a catalytic coke conversion of 97.32% in the presence of La 0.2 Sr 0.8 FeO 3 was achieved, which was 2.09 times the value without a catalyst. The research results provide a certain theoretical basis for catalytic heterogeneous reactions. [Display omitted] • The increase of oxygen vacancies promotes the adsorption of water molecules. • The increase of Fe valence state promotes water decomposition. • La 0.2 Sr 0.8 FeO 3 catalyzes water splitting to form adsorbed and free •OH radicals. • Absorbed •OH radicals mainly promotes the reaction of graphite carbon with steam. [ABSTRACT FROM AUTHOR]