**Preface**

The increasing demands for fine and high value-added chemicals have motivated the long-term exploration of high-performance catalysts with desired activity, selectivity, and durability. Owing to its high natural abundance and low cost, copper as well as its various derivatives has been widely employed as a catalytically active component in a diversity of organic transformations. On the other hand, the multiple accessible oxidation states of reactive Cu element (Cu0, CuI, CuII, and CuIII) within Cu-based catalysts are likely to enable the target catalytic reactions that proceed via both single- and multi-electron transfers. As a result, Cu-based catalysts have also found many applications in redox reactions, such as CO oxidation, selective oxidation of organic compounds, selective catalytic reduction of NOx by CO (CO-SCR), electrochemical hydrogen evolution reaction (HER), and electrochemical CO<sup>2</sup> reduction reaction (CO2RR). While a great progress has been made, the prerequisite for successful application of Cu-based catalysts lies in the delicate design and regulation of the local electron structure of active sites. Besides that, the catalytic activity of real Cu-based catalysts can only be predicted to some extent via theoretical modeling and calculations. Therefore, it is still of great significance to continue the exploration of novel and more efficient Cu-based catalysts that deliver an enhanced performance.

This Special Issue, entitled "Synthesis and Applications of Copper-Based Catalysts", provides an overview of recent progress in the synthesis and application of Cu-based materials, with particular emphasis on the latest advanced synthetic approaches, structure modulation strategies, and catalytic performance of copper-based catalysts in heterogeneous and homogeneous catalysis, which can contribute to the development of efficient Cu-based catalysts. We hope that our compilation of such meaningful research studies can provide researchers with new inspiration in this field.

> **Yongjun Ji, Liwen Xing, and Ke Wu** *Editors*
