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Application of Subcritical Water for Production of ZnO Nano-Catalyst

K. Paoplook, M.N. Eshtiaghi

The effect of process parameters (temperature and time) on preparation of ZnO nano catalyst using subcritical water was investigated. The amount of produced ZnO catalyst was dependent on temperature during subcritical water treatment. Increasing the temperature from 120 to 180 C decreased the ZnO catalyst with particle size larger than 2.5 μm. In contrast the amount of nano sized ZnO catalyst increased rapidly when increasing the process temperature. Up to about 50 % nano sized Zno catalyst could be produced at 180 C and 4 h reaction time. In general the total produced Zno catalyst using subcritical water was more than 2 times higher than conventionally prepared ZnO. Interestingly the ZnO catalyst prepared by subcritical water showed distinctly higher (up to 0.96 g/ml) bulk density compared to conventional prepared ZnO (about 0.47 g/ml). The Hemmet indicators have shown that the subcritical water prepared catalyst was higher basic strength than the conventionally prepared catalyst. The FTIR investigation of samples has shown that the subcritical water prepared catalyst has more impurities than the conventionally prepared ones. Additional experiments are necessary to determine the type of impurities in ZnO catalyst prepared by subcritical water method.