Selective phenol hydrogenation under mild condition over Pd catalysts supported on Al2O3 and SiO2
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Cyclohexanone (CHONE) is the key intermediate in the manufacture of nylon-6 and nylon-66. Selective hydrogenation of phenol into CHONE was investigated over Pd/SiO2 and Pd/Al2O3. The results show that the yield of CHONE reaches 98% or more over Pd/Al2O3 and Pd/SiO2 at 333 K under atmospheric pressure in cyclohexane solvent. High activity of Pd/Al2O3 is promoted by Lewis acidity, and phenol can be converted 100% within 300 min. The hydrogenation of CHONE occurs until the conversion of phenol approaches completion. Pd/SiO2 with smaller Pd nano-particles presents higher selectivity. For polar solvent, such as ethanol and dichloromethane, the activity of Pd catalysts decreases greatly. Auxiliary experiments verify that phenol adsorbs on Pd catalysts via the formation of π–c with an aromatic ring. Increased hydrogen pressure not only promotes significantly the rates of hydrogenation, but also increases the selectivity for CHONE, especially over Pd/SiO2-1 catalyst.
KeywordsCatalytic hydrogenation Solvent effect Pd Phenol Cyclohexanone
We would like to acknowledge the National Key Research and Development Program of China (no. 2016YFC0204300) and National Natural Science Foundation of China (nos. 21477036 and 21777043).
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