Influence of alkali promotion on phenol hydrogenation activity of palladium alumina catalysts

A series of alkali metals (Li, Na, K and Cs) promoted alumina-supported pal ladium catalysts prepared by wet impregnation method were characterised by XRD and CO chemisorption measurements. The samples were evaluated for the g as phase hydrogenation of phenol to cyclohexanone in a fixed-bed micro reac tor at 503 K under normal atmospheric pressure. The promoted palladium cata lysts show a higher rate of phenol conversion and yield of cyclohexanone th an unpromoted catalyst. Despite similar activity and selectivity for cycloh exanone between lithium- and sodium-promoted catalysts, the Na-promoted one s show a higher resistance for coke formation. The increase in the intrinsi c activity of the palladium site on alkali promotion has been attributed to the increase in phenol activity of the promoted catalysts. (C) 1999 Elsevi er Science B.V. All rights reserved.