Calcined Mg/Al hydrotalcites (CHTs) with various atomic ratios of Mg/Al were prepared and used as supports for palladium catalysts. Selective hydrogenation of phenol to cyclohexanone was investigated over Pd/CHT catalysts and compared with Pd/Al2O3, Pd/SiO2, Pd/CaO-Al2O3 and Pd/MgO. The Pd/CHT(2-4) catalysts showed high reactivities and selectivities to cyclohexanone, reaching 95% selectivity with 40% conversion. For Pd/CHT(2-4) catalysts, the calcined hydrotalcites exhibit strong base sites that were more effective than acid sites to affect the selectivity of cyclohexanone. The 0.3%Pd/CHT(2) catalyst was a good candidate for one-step process of cyclohexanone formation. On it the reaction orders of rate were found to be 2 with respect to the hydrogen pressure and -1 with respect to the partial pressure of phenol. (C) 1999 Elsevier Science B.V. All rights reserved.
