Influence of the charge transfer capacity of alkali and alkaline earth metals as promoters in the hydrogenation of phenol over palladium and nickel catalysts

The gas phase hydrogenation (523-573 K) of phenol has been studied over 1 w t.% Pd/Al2O3 and 1 wt.% Ni/SiO2 catalysts doped with Group I and II promote r oxides. A direct correlation between catalytic activity and the charge tr ansfer capacity of the promoters is presented where hydrogenation is favore d by increasing electron donation from the promoter. The Pd catalysts gener ated cyclohexanone (selectivity > 97%) as the predominant product; selectiv ity was unaffected by the presence of the alkali or alkaline earth dopants. The Ni system exhibited appreciable hydrogenolysis behavior and charge tra nsfer from the dopants limited the degree of hydrodeoxygenation to favor co mplete hydrogenation to cyclohexanol.