Pd–Co based spinel oxides derived from pd nanoparticles immobilized on layered double hydroxides for toluene combustion

Noble metal nanoparticles (noble metal NPs, noble metal = Ag, Pt and Pd) have been successfully immobilized on CoAl-layered double hydroxide (CoAl-LDHs) layers using a simple and facile self-redox process to afford noble metal NPs immobilized on CoAl-LDHs (N–CoAl-LDHs, N = Ag, Pt and Pd). In addition, the CoAl-LDHs and N-CoAl-LDHs were calcined in air at 600 °C to afford the CoAlO and N-CoAlO catalysts for toluene combustion. The catalytic and characterization results indicated that the Pd–CoAlO catalyst exhibited the highest catalytic activity because it possessed the highest low-temperature reducibility and the most abundant surface Co3+ and surface adsorbed oxygen species. In addition, the noble metal NP sizes of the N–CoAlO catalysts affected the catalytic activity for toluene combustion, and the existence of catalytically active PdO contributes to the excellent catalytic activity of the Pd–CoAlO catalyst for toluene combustion. The comparison experiments reveal that the PdO phase and CoAlO support play significant role in the toluene combustion and they participate cooperatively in the reaction process. In addition, the in situ DRIFTS results indicated that the benzoate species are the main intermediate species in toluene combustion, which should be further oxidized by O2 to the final products (i.e., CO2 and H2O).