Effect of ionic radius on soot oxidation activity for ceria-based binary metal oxides

CeO₂ (C) along with binary metal oxides of Ce_0.9M_0.1O_2-δ (M = Sn, Hf, Zr, Gd, Sm, and La; CT, CH, CZ CG, CS, and CL) are synthesized using the EDTA–citrate method. Samples having an ionic radius smaller (CT, CH, and CZ) and larger (CG, CS, and CL) than Ce⁴⁺ are classified separately, and their soot oxidation activity is analyzed. The incorporation of dopant is confirmed from lattice constant variation in X-ray diffraction result. The critical descriptors for the activity are dopant nature (ionic radius and oxidation-state), single-phase solid solution, lattice strain, reactive (200) and (220) planes, Raman intensity ration (I_ov/I_F2g), optical bandgap, reducibility ratio, and surface oxygen vacancy. Smaller ionic radius, isovalent dopants (CH and CZ) create a defect site by lowering the optical bandgap along with improved surface oxygen vacancy concentration and thus enhanced soot oxidation activity. Aliovalent dopant with larger ionic radius shows the involvement of lattice oxygen in oxidation reaction by charge compensation mechanism. CL showed the highest activity amongst larger ionic radius samples.