The genesis of the active phase in Raney-type catalysts: the role of leaching parameters

The morphology and microstructure of two commercial 50-50 wt.% nickel aluminium alloys (A and B) have been studied. As expected from the phase diagram, NiAl3, Ni2Al3 and a small amount of metallic aluminium were observed. The distribution of the two main phases consists of a core of Ni2Al3 with a shell of NiAl3. Even if the composition of the starting alloys was the same, the amounts of the different phases are different: more Ni2Al3 and less metallic aluminium were present in alloy B. Treatment with an aqueous sodium hydroxide solution (leaching process) leads to Raney-type nickel catalyst. Different leaching times were used in order to follow an evolution in the morphology of the catalysts. The activation process is very fast and after 10 s of leaching, most of the aluminium has been leached out and is present as alumina. The longer the leaching time, the better the catalytic performance (both activity and selectivity) of the catalysts. This evolution of catalytic performance as function of time is much more pronounced in the case of catalysts issued from alloy A. 2003 Elsevier Science B.V. All rights reserved.