Formic acid is a high-prospect energy carrier of sustainable H2 and can also favorably supply sustainable H2 to hydrogenation catalysts in replacement of external pressurized H2. A solar photon-assisted synthesis method was successfully implemented for decorating a ceriamodified TiO2 support with ultra-dispersed Ru nanoclusters with a large fraction of low atomicity species and Ru single atoms. Adding ceria to the TiO2 support at a quarter of the theoretical monolayer is a suited surface modification for partially reducing the detrimental intrinsic activity of the bare TiO2 surface for the dehydration of formic acid, what allows the undesired formation of CO to be mitigated and higher selectivities to H2 to be achieved when using the Ru/CeO2/TiO2 catalyst. The dual (combined) photonic/thermal excitation of the Ru/CeO2/TiO2 catalyst boosted the H2 production rate and allowed the dehydrogenation reaction to be conducted at a lower temperature compared to the dark conditions, for instance with a 80°C downshift at 190°C, what corresponded to a 42% relative gain compared to the dark conditions. Advanced electron microscopy characterization has been crucial to unveil the atomic-level nature of the Ru/CeO2/TiO2 photo-thermo catalyst, bringing to light the presence of ultra-dispersed metallic Ru nanoclusters, both (i) decorating nanometric size flat CeO2 nanoparticles interfaced in epitaxy with high-index TiO2 facets, and (ii) being homogeneously distributed over the TiO2 surface in close vicinity with low atomicity CeO2 species.