The application of {(DMF)10Yb2[TM(CN)4]3}∞ (TM = Ni, Pd) supported on silica to promote gas phase phenol hydrogenation

The catalytic gas phase phenol hydrogenation activities/selectivities associated with Pd/SiO2 prepared by Pd(NO3)(2) and Pd(C2H3O2)(2) impregnation have been compared with those delivered by Pd-Yb/SiO2 prepared from a {(DMF)(10)Yb-2[Pd(CN)(4)](3)}(infinity) precursor. The Pd metal loading spanned the range 1-10% (w/w) and the reaction was conducted over the temperature interval 398-448 K. Phenol hydrogenation yielded both cyclohexanone as a partially hydrogenated reactive intermediate and cyclohexanol as the fully hydrogenated product. The activated catalysts have been characterized by HRTEM/EDX, XPS and XRD. The reaction exhibits a slight dependence on Pd particle size with a lower specific hydrogenation activity associated with larger Pd particles. The incorporation of Yb resulted in an appreciable enhancement of phenol conversion. Yb/SiO2, however, did not exhibit any hydrogenation activity and the promotional effect of Yb in Pd-Yb/SiO2 is tentatively attributed to hydrogen transfer via surface Yb hydride. The effect of contact time and reaction temperature on activity/selectivity has been considered and is discussed in terms of phenol/catalyst interaction(s). The promotional effect of Yb also extends to phenol hydrogenation over supported Ni (5%, w/w Ni) where Ni-Yb/SiO2 delivered higher conversions and higher overall cyclohexanone yields when compared with Ni/SiO2. (C) 2003 Elsevier B.V. All rights reserved.