Improved and Reduced Performance of Cu- and Ni-Substituted Co₃O₄ Catalysts with Varying Co_Oh/Co_Td and Co³⁺/Co²⁺ Ratios for the Complete Catalytic Oxidation of VOCs

Abstract

The Co3O4 spinel is one of the most promising transition metal oxide (TMO) catalysts for volatile organic compound (VOC) treatment. Substituting effects have usually been utilized to improve the catalytic performance of the Co3O4 spinel. In this study, Cu- and Ni-substituted Co3O4 catalysts derived from mixed metal–organic frameworks (MMOFs) retained similar spinel structures but exhibited improved and reduced performance for o-xylene oxidation, respectively. Physicochemical characterization and DFT calculations revealed that Cu and Ni substitution into the Co3O4 spinel varied the valence (Co3+/Co2+) and geometry (CoOh/CoTd) distributions of Co cations through different partial electron transfer and substitution sites. The higher Co3+/Co2+ and CoOh/CoTd ratios of the CuCo2O4 catalyst contributed to the superior reducibility and oxygen mobility, which facilitated the oxidation of intermediates at lower temperatures in the catalytic oxidation of o-xylene. Meanwhile, the NiCo2O4 catalyst with lower Co3+/Co2+ and CoOh/CoTd ratios could not completely oxidize intermediates under the same conditions due to inferior redox properties. Therefore, the CuCo2O4 catalyst showed superior catalytic activity and stability to the NiCo2O4 catalyst for the catalytic oxidation of o-xylene. This work provides insights into the synthesis of substituted Co3O4 catalysts from MMOFs and mechanism of substituting effects, which might guide the design of efficient TMO catalysts for VOC treatment.

Review and Perspectives of Enhancement in the Catalytic Stability for the Complete Combustion of CO, CH4, and Volatile Organic Compounds

“…The catalytic performance of the Cu-and Ni-substituted Co 3 O 4 for o-xylene oxidation was related to the reducibility and oxygen mobility. 42 As shown in Figure 2C, the Cu-substituted catalyst (CuCo 2 O 4 ) presented better catalytic activity and stability. A partial electron was transferred from Co 2+ to Cu 2+ with stronger electronic affinity or from Ni 2+ to the more electrophilic Co 3+ through the adjacent lattice oxygen, causing an increase and decrease in the Co 3+ /Co 2+ molar ratio, respectively.…”

“…(D, E) Oxygen vacancy formation for the MCo 2 O 4 catalysts. Reproduced with permission from ref . Copyright 2022 American Chemical Society.…”

High-Efficiency Electrochemical Nitrate Reduction to Ammonia on a Co3O4 Nanoarray Catalyst with Cobalt Vacancies

“…The intensity of the broadened peak around 682 cm –1 for v Co -Co 3 O 4 /CC obviously increases, which can be associated with the change in the long-range order of the crystal, indicating that more defect sites are formed on v Co -Co 3 O 4 /CC . The binding energies at 682 and 192 cm –1 are attributed to the octahedral sites (CoO 6 ) and tetrahedral coordination (CoO 4 ) of the crystalline Co 3 O 4 phase, respectively. , The intensity ratio of Raman peaks ( I 192 / I 682 ) is computed to assess the proportion of CoO 4 /CoO 6 . The I 192 / I 682 ratio of v Co -Co 3 O 4 /CC (0.62) increases compared with Co 3 O 4 /CC (0.51), indicating that Al 3+ preferentially occupied the octahedral sites of Co 3 O 4 , further demonstrating that the etching of Al 3+ leads to Co 3+ vacancy.…”

“…45,46 The intensity ratio of Raman peaks(I 192 /I 682 ) is computed to assess the proportion of CoO 4 /CoO 6 . The I 192 /I 682 ratio of v Co -Co 3 O 4 /CC (0.62) increases compared with Co 3 O 4 /CC (0.51), indicating that Al 3+ preferentially occupied the octahedral sites of Co 3 O 4 , further demonstrating that the etching of Al 3+ leads to Co 3+ vacancy.…”

Recent progress on catalysts for catalytic oxidation of volatile organic compounds: a review

“…The spinel CoMn 2 O 4 achieved a 100% conversion of toluene at only 220 °C, which was attributed to the larger surface area, rich cationic vacancies, and high mobility of oxygen species. Very recently, Ma et al 305 reported Cu- and Ni-substituted Co 3 O 4 spinel catalysts, namely MCo 2 O 4 (M = Cu or Ni), utilizing mixed metal organic frameworks as the precursor, which exhibited significantly altered performance for o -xylene oxidation. The results of XPS and XANES displayed the low oxidation state of Cu ions and high oxidation state of Ni ions, which resulted in the increased Co 3+ /Co 2+ ratio in CuCo 2 O 4 and the decreased Co 3+ /Co 2+ ratio in NiCo 2 O 4 , demonstrating the various electron transfers between Cu(Ni) atoms and Co atoms in MCo 2 O 4 .…”