The Dynamic Mechanism of Ozone Decomposition over Layered Nickel Catalysts: Crystalline Phase Evolution Dictates...

Nickel-based layered materials have attracted considerable attention due to their high efficiency in ozone decomposition and related advantages. Despite unclear ozone decomposition mechanisms, this study synthesized nickel hydroxide to systematically investigate their catalytic performance and structural evolution, aiming to elucidate the critical relationship between the catalyst's crystalline structure and its activity. The results indicate that Ni(OH)₂ transforms into NiOOH during ozone decomposition, with catalytic activity determined by the crystalline phase of the resultant NiOOH species. Ni(OH)₂ enriched with hydroxyl groups tends to experience deep oxidation, yielding γ-NiOOH characterized by an expanded interlayer spacing. This phase exhibits superior ozone decomposition efficiency, sustaining an ozone conversion rate exceeding 93% under conditions of 80% relative humidity and a space velocity of 840 L·g^-1·h^-1. Conversely, catalysts that form β-NiOOH demonstrate lower activity. DFT calculations confirm that γ-NiOOH significantly lowers the energy barrier for ozone decomposition. The surface oxygen sites of γ-NiOOH facilitate rapid desorption of oxygen intermediates, effectively mitigating catalyst deactivation. Moreover, DFT analyses indicate that γ-NiOOH possesses a more favorable ozone decomposition mechanism relative to β-NiOOH. This study elucidates the dynamic transformation mechanism of layered nickel hydroxide catalysts during ozone decomposition and underscores the pivotal role of γ-NiOOH in this process.