The Cu/ZrO2/CeO2 (CZC) catalysts were synthesized from metal sols, prepared from the appropriate amounts of the mixed precursors (NH4)2Ce(NO3)6, ZrO(NO3)2Ã—H2O and Cu(NO3)2Ã—2.5 H2O (all solutions are Aldrich products of > 99% purity), dissolved in 40 ml of distilled water. The total metal content of the resulting sol was 5Ã—10-3Â mol. By increasing the pH above 10 through addition of NaOH solution, the co-precipitation of the metal sols as metal hydroxides was achieved. The resulting precipitate was repeatedly washed with distilled water until pH=7 was obtained. The solution was then suspended in a mixture of 5 ml of distilled water and a calculated amount of 90% HNO3 obtained. Depending on the sample composition, the HNO3/metal molar ratio was varied between 1:1 and 1.5:1. Ultrasonic treatment of the suspension for 45 â€“ 60 min resulted in the formation of a transparent sol.
Templating process was carried out by using XAD-16 non-functionalized polystyrene beads (a Sigma product); with a specific surface area of 800 m2g-1Â and an average pore diameter of 10 nm. 1.5 ml of the wet beads and 0.005 mol of the metal sol were mixed together and then heated in an oven at 333 K for 2 days in order to ensure solvent evaporation. In a subsequent manner, the beads were dried at 373 K for one extra day and the rinsed thoroughly with distilled water to remove excess deposit from their surface. Later, the beads were dried at 333K for 1 day and then calcined in an oven at 773 K in a N2 stream of 100 ml/min for 2.5 h and then for an additional 8 h in air. After calcinations
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