Cu-based metal oxide catalysts for NH₃-SCR of NO_x: From fundamentals to mechanistic insights

In today's world, emissions from automobile exhaust and industrial chimneys are the major contributors to atmospheric nitrogen oxides (NO_x). NO_x has detrimental effects on both plants and animals and can cause various diseases. Ammonia (NH₃)-based selective catalytic reduction (SCR) is a highly effective method for controlling and mitigating NO_x emissions. Cu-based oxides are extensively utilized in NH₃-SCR processes due to their widespread availability, cost-effectiveness, and outstanding redox capabilities, making them a preferred choice among MO catalysts. The presence of copper in both Cu²⁺ and Cu⁺ oxidation states offers favorable potential for combination with other transition elements, enhancing catalytic performance. In addition, the synthesis methods use in the SCR process, regeneration, and disposal of Cu-oxide-based catalysts are more cost-effective and environment friendly than those of precious metal oxide SCR catalysts, making Cu-based technology a more sustainable and economical choice. While numerous review papers have explored the role of copper in zeolite-based catalysts for NO_x reduction but concise reports focusing on Cu in MO-based catalysts for SCR remain scarce. Therefore, in this work, we aim to review the synthesis methods, reaction mechanisms, structure-activity relationships, economic feasibility, environmental impact assessment and durability of Cu-based oxide catalysts in NH₃-SCR, particularly against water, alkali and alkaline earth metals, SO₂, and other relevant factors.