PREPARATION AND CHARACTERIZATION OF SILICA-SUPPORTED COPPER-CATALYSTS FOR THE DEHYDROGENATION OF CYCLOHEXANOL TO CYCLOHEXANONE

Copper dispersed on an alkali-doped silica support, when properly prepared using a precipitation method, was found to be better than CuMgO and CuZnO as regards conversion, selectivity, and especially resistance against sintering for the dehydrogenation of cyclohexanol to cyclohexanone. The optimum precipitation conditions were a precipitation temperature of 90-degrees-C, a precipitation time of 4 h and the final pH of the solution higher than 9. The high solution pH was intended to neutralize acidic sites of the support, which were responsible for the formation of side products. The lowest copper loading was desirable to achieve the highest conversion, but the copper loading should be kept above 12% to suppress effectively the formation of side products on the alkali-treated silica surface. Temperature-programmed reduction, X-ray diffraction, transmission electron microscopy and reaction tests revealed that catalysts prepared under the above conditions had highly dispersed metallic copper particles stabilized on a neutralized silica surface.