Characterization and dehydrogenation activity of Cu/Al2O(3) catalysts prepared by electroless plating technique

Seven new alumina supported copper catalysts prepared by the electroless copper plating method and the support itself were investigated to characterize by X-ray diffraction (XRD), scanning electron micrography (SEM) and electron probe microanalysis (EPMA). Dehydrogenations of isopropanol and cyclohexanol were individually conducted to test the activity of these catalysts. The copper surface area was measured by the selective chemisorption of nitrous oxide and the acidity was measured by the chemisorption of ammonia using the volumetric method. Besides the BET surface area, pore size distribution was also measured. The results showed that the BET surface area linearly decreased with the copper loading of the catalyst. Copper formed crystallites at a minimum loading (ca. 7 wt.% Cu) and the crystallite diameter (d(B)) was almost independent of loading. The copper surface area increased with copper loading up to ca. 15 wt.% Cu and then decreased with further deposits. The acidity of catalyst also decreased with copper loading up to a certain copper content, further deposition of copper had no significant effect on it. The catalysts prepared by the electroless plating method showed a relatively higher acidity than the catalysts prepared by the precipitation method. It was found that the dehydrogenation activity strongly depended upon the free exposed copper sites available for alcohol adsorption and reaction and the selectivity was a function of acidity of the catalysts as well as the reaction temperature.