Synchrotron X-ray microtomography of Raney-type nickel catalysts prepared by gas atomisation: Effect of microstructure on catalytic performance

Synchrotron X-ray microtomography (SXRM) was used to examine the microstructure of various Ni–Al alloys prepared by gas atomisation. The resulting Raney-type nickel catalysts that were activated by chemical treatment with a concentrated sodium hydroxide solution (20 wt% in water) were also studied. The main objective of this work is to correlate the microstructure of various Ni–Al alloys prepared by gas atomisation and the catalytic performance of the resulting Raney-type nickel catalysts. It appears that a NiAl3/Ni2Al3 ratio around 2.3 in the precursor alloy prepared by gas atomisation favours the formation of a dendritic network in the atomised spherical particle. The spherical shape of the particle and the dendritic network are still present after the leaching process in the Raney-type nickel catalysts. After activation, the interdendritic space forms a macroporous network that is directly linked to the catalytic performance. Parameters of the precursor alloy, i.e. particle size, phase composition, are chosen to obtain an optimal catalytic performance. In this way, an activity is obtained that is at least a factor of 2 higher than that of alloys prepared by the commercial cast-and-crush method. Inductively coupled plasma optical emission spectroscopy (ICP-OES) and BET measurements were used for bulk analysis and determination of the surface area, respectively. Hydrogenation of nitrobenzene and butyraldehyde were used as test reactions. A model that directly correlates the microstructure of a precursor alloy processed by gas atomisation and the catalytic performance of the resulting catalyst is proposed.