G. Neri et al., HYDROGENATION OF PHENOL TO CYCLOHEXANONE OVER PALLADIUM AND ALKALI-DOPED PALLADIUM CATALYSTS, Applied catalysis. A, General, 110(1), 1994, pp. 49-59
Palladium catalysts supported on Al2O3 and MgO were prepared and used
in the gas-phase hydrogenation of phenol to cyclohexanone. In all rang
e of conditions investigated, selectivity to cyclohexanone was higher
on Pd/MgO than on Pd/Al2O3. On Pd/Al2O3 the reaction rates were found
to be of first order with respect to the phenol partial pressure and s
econd order with respect to the hydrogen pressure. On Pd/MgO, instead,
the order of reaction with respect to phenol was - 1 and the order wi
th respect to hydrogen was about 1. Addition of alkali or alkaline ear
th metals (Ca, K, Cs) to Pd/Al2O3 increased the activity and the selec
tivity to cyclohexanone without modifying the orders of reaction. On t
he basis of the results of this study, a reaction mechanism involving
adsorption of phenol on the sites of the support at the interface of t
he palladium metal particles is proposed. The higher selectivity to cy
clohexanone found on Pd/MgO compared to Pd/Al2O3, is explained by two
different forms of adsorbed phenol.