Unraveling the role of oxygen vacancies in metal oxides: Recent progress and perspectives in NH3-SCR for NOx removal

As the most efficient NOx removal technology, selective catalytic reduction with ammonia (NH3-SCR) has garnered increasing attention. Oxygen vacancies (OVs) in catalysts facilitate the reactants adsorption and promote the redox reactions, representing a significant strategy to enhance SCR performance. Transition metal oxide catalysts are extensively used for their elevated activity and stability, but challenges such as limited temperature range for catalytic activity and inadequate resistance to SO2 remain unresolved. This work systematically categorizes the classification, construction strategies, structural characterization of OVs, and summarizes their specific mechanisms in SCR. Specifically, the selective adsorption of OVs and their interaction with reactant molecules during SCR reactions are emphasized. However, accurate control of the oxygen vacancies distribution and its long-period stability still remain challenges. The rational regulation of oxygen vacancies based on their classification and the reversibility between surface and bulk oxygen vacancies offer novel insights to address this issue. This paper also provides an outlook, which is beneficial for future guidance on the targeted construction of oxygen vacancies according to different catalytic scenarios. The ideas elucidated in this review help to provide instruction for the synthesis and the mechanism explanation of OVs on the catalysts.