<p>Rare-earth metal oxide CeO₂ with a unique electronic structure has always been one of the popular research materials in the field of catalysis. However, due to its inherent band structure limitations and the recombination of photo-generated carriers, its photocatalytic performance still needs to be rationally optimized and improved. Here, an in situ assembly method was employed to construct 3D/2D CeO₂/Bi₂MoO₆ (Ce/BMO) S-scheme heterojunctions for enhanced tandem reaction of photocatalytic secondary amines synthesis. Experimental results and density functional theory calculations reveal that the transfer of photo-generated carriers between CeO₂ and Bi₂MoO₆ (BMO) conforms to the S-scheme heterojunction mechanism which regulates the band structure and greatly promotes the separation and effective utilization of photo-generated carriers. In situ Fourier-transform infrared (in situ FTIR) spectra and adsorption energy calculations demonstrate that the unique Ce³⁺/Ce⁴⁺ component in CeO₂ promotes the nitrobenzene adsorption and the unsaturated Mo sites on Bi₂MoO₆ are responsible for benzyl alcohol adsorption, which is highly favorable for surface oxidation and reduction reactions. Thus, the optimal 0.7-CeO₂/Bi₂MoO₆ (0.7Ce/BMO) exhibited a 93% conversion rate of nitrobenzene and a 91% selectivity for secondary amines. This work emphasizes the crucial role of S-scheme heterojunctions for constructing efficient rare-earth metal oxide-based composite photocatalysts.</p> Graphical abstract <p></p>