Phenol Hydrogenation to Cyclohexanol Catalysed by Palladium Supported on CuO/CeO2

Selective hydrogenation of phenol to cyclohexanol, an industrially important reaction over Pd-CuO/CeO₂ showed very high efficiency under mild conditions. Palladium loading on CuO/CeO₂ led to hydrogen spillover on the catalyst surface increasing the oxygen vacancies helping activation of phenol as phenoxide ion with perpendicular orientation of aromatic ring on catalyst surface as evident from FTIR studies.

Abstract

Hydrogenation of phenol to cyclohexanone/cyclohexanol is an important reaction in production of nylon-6, nylon-66 and in petroleum industry. Liquid phase phenol hydrogenation over Pd-CuO/CeO₂ was carried out under mild conditions. Palladium impregnated over CuO/CeO₂ synthesized by co-precipitation method showed excellent catalytic activity for phenol hydrogenation (99% conversion with 80% cyclohexanol yield) at 90 °C and 10 bar H₂ pressure in water. Commercial 10%Pd/C showed only 8% phenol conversion under identical conditions. The detailed characterization revealed significant improvement in surface area of ceria after addition of CuO and decrease in crystallite size with creation of defects in CeO₂ lattice. XPS analysis showed Pd loading on CuO/CeO₂ to cause hydrogen spillover on the surface leading to increase in the oxygen vacancies. The interaction of phenol with catalyst surface studied by detailed FTIR analysis, revealed activation of phenol on oxygen vacancy of ceria as phenoxide ion with perpendicular orientation of aromatic ring on catalyst surface.

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