Gas-phase hydrogenation of 4-tert-butylphenol over Pt/SiO2

Influence of modifiers on the performance of Ru-supported catalysts on the stereoselective hydrogenation of 4-acetamidophenol

“…It can be observed that the velocity constants for the modified catalysts were lower than for the parent catalyst in both series, carbon and alumina-supported catalysts, although the effect was more pronounced for the carbon-supported catalysts. Similar decrease in the hydrogenation rate was reported for Pt/SiO 2 doped with Ca in the hydrogenation of 4-tert-butylphenol [22]. Contrary to what it has been reported before [5,6], in the present case the differences in dispersion between modified and non-modified catalysts (Table 1) were not so relevant to explain the reduction observed in the activity values, especially for carbon-supported catalysts where the velocity constant was reduced three orders of magnitude.…”

“…While for Pd catalysts the keto form is finally desorbed [10,25], the hydrogenation of this intermediate in the hydrogenation of paracetamol (Scheme 1) is fast for our Ru-catalysts, and, leads directly to the 4-acetamidocyclohexanols. On the other hand, the formation of cis and trans isomers in the hydrogenation of alkylsubstituted phenols seems to depend on the keto-enol equilibrium of the partially hydrogenated intermediate and the subsequent hydrogenation of both forms [22,26,27]. The acid-base properties of the surface can affect this equilibrium and may account for the increase observed in the selectivity to trans-4-acetamidocyclohexanol for the modified samples.…”