Selective Phenol Hydrogenation to Cyclohexanone Over a Dual Supported Pd–Lewis Acid Catalyst

Abstract

Cyclohexanone is an industrially important intermediate in the synthesis of materials such as nylon, but preparing it efficiently through direct hydrogenation of phenol is hindered by over-reduction to cyclohexanol. Here we report that a previously unappreciated combination of two common commercial catalysts-nanoparticulate palladium (supported on carbon, alumina, or NaY zeolite) and a Lewis acid such as AlCl3-synergistically promotes this reaction. Conversion exceeding 99.9% was achieved with >99.9% selectivity within 7 hours at 1.0-megapascal hydrogen pressure and 50 degrees C. The reaction was accelerated at higher temperature or in a compressed CO(2) solvent medium. Preliminary kinetic and spectroscopic studies suggest that the Lewis acid sequentially enhances the hydrogenation of phenol to cyclohexanone and then inhibits further hydrogenation of the ketone.

Hydrogenation of phenol with supported Rh catalysts in the presence of compressed CO2: Its effects on reaction rate, product selectivity and catalyst life

“…On the basis of these results, it can be concluded that the phenol hydrogenation proceeds through the pathways illustrated in Scheme 1: phenol is sequentially hydrogenated through cyclohexanone to cyclohexanol (paths i and iii) and directly to cyclohexanol (path ii). In contrast to the present results, almost 100% selectivity to cyclohexanone was obtained with supported Pd catalysts in both the gas-phase [1][2][3][4][5][6][7][8][9][10][11][12] and liquid-phase [13][14][15][16]25] hydrogenation reactions. The direct formation of cyclohexanol from phenol (path ii) is unlikely to occur with these Pd catalysts.…”

“…This may result from stronger acidity of Al 2 O 3 support compared with active carbon. Liu et al point out the significance of Lewis acidity of support materials in determining the high selectivity to the formation of cyclohexanone, which is prevented from being hydrogenated to cyclohexanol by interactions between the acid sites and the cyclohexanone [25]. Table 3 The effects of CO 2 pressurization were greatly different between Rh/C and Rh/Al 2 O 3 catalysts.…”

“…Recently, Liu et al revealed the synergistic effect of supported Pd particles and solid Lewis acid sites for the selective hydrogenation of phenol to cyclohexanone [25]. The acid sites interact with C=O of cyclohexanone, preventing its further hydrogenation to the undesired cyclohexanol [25].…”

“…Recently, Chatterjee et al have screened several supported catalysts using different noble metals and supports and found that Pd on Al-MCM-41 is effective to the hydrogenation of phenol to cyclohexanone in dense phase CO 2 (12 MPa) [24]. Very recently Liu et al indicated an interesting synergistic effect of supported Pd particles and solid Lewis acid, with which the hydrogenation of phenol to cyclohexanone was achieved in almost 100% selectivity under mild conditions [25].…”

Confined Pt and CoFe2O4Nanoparticles in a Mesoporous Core/Shell Silica Microsphere and Their Catalytic Activity

“…[36][37][38][39] The underlying origin of the metal-support interaction and the promotional role of the active oxide supports in enhancing the catalytic activity and selectivity have thus been extensively studied. [40][41][42][43][44][45][46][47] Relatively, little is known about direct interfacial interaction between metal NPs and support oxide NPs in a confined geometry. It would thus be interesting to study noble metal and active metal oxide with a welldefined nanostructure, which will render an important clue to elucidate the proximal metal-oxide interaction in nanometer scale [48][49][50] and will also give a chance to develop a hybrid catalytic system on the basis of metal and oxide.…”