Nickel crystallite size and net activity of hydrogenation catalysts

and Summary Among supported nickel‐based hydrogenation catalysts, the Ni crystallite size apparently plays a secondary role in net hydrogenation activity for undistilled tallow fatty acids and nonselective hydro‐genation of oxidized soybean oil. The nickel crystal‐lite size measured by the x‐ray diffraction profile broadening technique of Scherrer varied between 55 A and 150 A. The commercial catalyst with the small‐est nickel crystallite size, in the samples studied, was not the most active for hardening soybean oil, while fatty acid hydrogenation showed a large crystallite catalyst to have the highest activity. Since the percent reduced nickel used in catalytic hydrogenation is not well known if the Ni/NiO ratio is poorly defined, relative activities were then correlated with qualita‐tive x‐ray diffraction measurements of the Ni/NiO values. Again, there was no trend in activity as a func‐tion of Ni/NiO. This apparent puzzle is probably due to real differences in the micro structure of the catalyst support. A series of experimental reductions using a common green catalyst led to very good cor‐relations between net activity for fatty acid hydro‐genation and the crystallite size and Ni/NiO ratio. On a given support, the crystallite dimension can be modified by the reduction treatment and is not sharply fixed by the selection of nickel salt and sup‐port. If the stoichiometric ratio of hydrogen is lowered, the crystallite dimension is reduced, but so is the qualitative efficiency of reduction (Ni/NiO), with the result that an exceptionally small crystallite size catalyst may be less active than one with larger crystals, but with more reduced Ni/unit weight.