Hierarchical MnOx/Co3O4 Nanoarrays on Ni Foam for Catalytic Oxidation of Volatile Organic Compounds

Hierarchical Co3O4/MnOx and MnOx/Co3O4 nanoarrays were successfully prepared by primary and secondary hydrothermal process on the Ni foam (NF), and the synthesized monolithic catalyst was used for catalytic combustion of toluene. Similarly, the monolithic Co3O4/NF, and MnOx/NF nanoarray catalysts were also prepared with the same method. Notably, toluene catalytic oxidation test proved that the catalytic performance of these monolithic catalysts followed this order: MnOx/Co3O4/NF > Co3O4/MnOx/NF > Co3O4/NF > MnOx/NF and the monolithic MnOx/Co3O4/NF catalyst showed the excellent toluene oxidation performance (T90 = 238 °C). Interestingly, the monolithic MnOx/Co3O4/NF catalyst also showed good stability for the toluene oxidation, which makes it a possible candidate to replace noble-metal catalysts. Through XPS and H2-TPR analysis, we are proved that the monolithic MnOx/Co3O4/NF catalyst has more active species (Co3+, Mn3+ and Mn4+), rich lattice oxygen, better interaction between Cobalt and Manganese, and excellent reducibility, which jointly promoted the conversion of toluene. In situ DRIFTs result over the monolithic MnOx/Co3O4/NF catalyst verified that the benzoate and anhydride species were the key intermediates of toluene catalytic combustion and the possible reaction path was likely as followed: toluene → benzoate → benzoquinone → maleate or maleic anhydride → formaldehyde or acrolein →··· → CO2 and H2O.