Fig. 7. (A) ln(C/C₀) versus t for the reduction of 4-NP catalyzed by (a) Cu–CeO₂–Pt; (b) Cu_0.66Co_0.34–CeO₂–Pt; (c) Cu_0.50Co_0.50–CeO₂–Pt; (d) Cu_0.34Co_0.66–CeO₂–Pt; (e) Co–CeO₂–Pt; (f) CeO₂–Pt. (B) Conversion in successive reaction cycles of Cu_xCo_1–x–CeO₂–Pt and CeO₂–Pt.