The reported promising catalysts for CO-PROX can be grouped into three classes: 1. Supported noble metal catalysts, such as Pt, Pd, Ir, Ru or Rh [46-74], 2. Nano-gold catalysts [75-94] 3. Base metal oxides catalysts which mainly concentrate on CuO-CeO2 [8-10, 45, 95-125].