Catalytic oxidation of multi-class VOCs over nickel-modified Co3O4: Comparative kinetic and surface analysis

Nickel-modified Co 3 O 4 catalysts with Ni:Co molar ratios ranging from 0 to 0.5 were synthesised and extensively characterised by ICP-AES, N 2 physisorption, XRD, Raman, SEM, STEM-HAADF, H 2 -TPR, O 2 -TPD, NH 3 -TPD, FTIR, XPS and EDX to evaluate their performance in the catalytic oxidation of volatile organic compounds (VOCs) of varying chemical nature: ethylene, toluene, and vinyl chloride. Nickel incorporation increased specific surface area, enhanced the concentration of active oxygen species and improved surface acidity, while reducing crystallite size. As a result, the modified catalysts exhibited superior activity compared to bare Co 3 O 4 . Toluene oxidation was mainly governed by surface oxygen availability, whereas ethylene oxidation was controlled by adsorption capacity on acid sites. In the case of vinyl chloride, nickel addition improved low-temperature activity (<250 ºC); however, in a consecutive reaction cycle, the probable formation of chlorinated nickel species induced partial deactivation, leading to increased T 50 values. Kinetic analyses revealed time on stream-dependent reaction mechanisms. In a broader context, these findings highlighted a VOC-dependent functionality of Ni sites, which modulate adsorption, activation and deactivation pathways depending on reactant chemistry. Overall, these results elucidate the dual role of nickel in Co 3 O 4 -based catalysts and provide guidance for the rational design of efficient, non-noble metal oxide catalysts for the total oxidation of structurally different VOCs. • Ni modified Co 3 O 4 catalysts were evaluated for structurally different VOCs oxidation. • Ni addition increased oxygen species and acidity while reducing crystallite size. • Toluene and ethylene oxidation linked to surface oxygen and acidity, respectively. • Vinyl chloride oxidation leads to chlorine accumulation and deactivation. • Multi-VOC kinetics showed that Ni functionality on Co 3 O 4 depends on VOC chemistry.