The promotion of a TiO2 photocatalyst by surface species consisting of cerium oxide and metal-promoted carbon nitride (g-C3N4) was analyzed to gain insight into the effect of Ca or Fe cationic species of the carbon nitride component in the overall performance of the photocatalytic system. The resulting materials were characterized with X-ray diffraction, time-resolved microwave conductivity (TRMC) and photoelectron, infrared, UV–visible and photoluminescence spectroscopies. The photoactivity of the materials in the gas phase elimination of toluene was evaluated under UV and sunlight-type illumination conditions and the corresponding true reaction quantum efficiency values calculated. The photoluminescence and TRMC analyses provide unequivocal evidence that the presence of Fe and Ca alter charge recombination to a different degree, leading to qualitatively different, promoting photochemical effects. This occurs exclusively in co-presence of ceria species at the titania surface and is thus characteristic of the ternary composite heterostructures.