The development of CuPS-cats over the past 20 years was summarized in Figure 3. There are five major approaches in CuPS synthesis, including examination of synthesis criterion, design of preparation method, selection of supports, addition of promoters, and control of PS morphology, and these topics will be discussed in Sections 2.1–2.5, respec- tively. Since a reduction step is necessary to transform CuPS into CuPS-cat, the reduction behavior of CuPS will be addressed in Section 2.6.