Rational tuning towards A/B-sites double-occupying cobalt on tri-metallic spinel: Insights into its catalytic activity on toluene catalytic oxidation

Abstract Promoting the catalyst reducibility is the key to the breakthrough of the catalytic oxidation technology. We prepared the layered double oxides (LDOs) spinel catalysts utilizing the layered double hydroxides (LDHs) as precursors. Innovatively, cobalt was applied as A/B-sites double-occupying cations. By introducing Cu(II) into the A-sites, we created a pushing effect towards the A-sites Co(II). The binding energy of Co 2p and the projected density of states energy of Co 3d shifted higher. The Co(II) gained greater momentum to convert to Co(III). The same pushing effect towards B-sites Co(III) were generated using B-sites occupying Ga(III), promoting Co(III) transfer towards lower valence state. Thus, the converting between Co(II) and Co(III) were speeded up. Moreover, the ionic radius differences between Cu(II) and Co(II) caused lattice distortion, enhancing the adsorbed oxygen species and surface oxygen defects. These contributed to the great improvement of reducibility and enhanced catalytic activity towards toluene oxidation.