Primary unsaturated fatty amines are typically produced by the hydrogenation of unsaturated fatty nitriles in a batch process with activated Ni catalysts, where the required level of carbon-carbon double bond retention is determined by the fatty amine's use. At low to moderate levels of nitrile conversion the metal's surface is completely covered with the adsorbed nitrile and practically no olefin adsorption takes place. At high levels of nitrile conversion the surface is not saturated and this allows the olefinic groups to adsorb and hydrogenate as the batch process comes to an end. We have drastically improved olefin retention at low nitrile coverages by controlling the active site's ensemble size via the deposition of carbonaceous residues onto the catalyst's surface. This stifled the co-adsorption of the weakly held olefinic groups during nitrile hydrogenation and enhanced their steric hindrance caused by their internal position along the fatty chain to give higher unsaturated primary fatty amine yields. These carbonaceous residues were formed by the decomposition of formaldehyde or sodium formate onto the catalyst's surface at different temperatures. Although these treatments slightly decreased the initial activity, all of them increased olefin retention [as calculated from iodine value (IV) titrations], decreased the titrated level of secondary and tertiary amines (2/3 A) and led to higher nitrile conversions [as determined by total amine value (TAV) titrations] within shorter reaction times. The formaldehyde treatment was preferred and gave the highest olefin retention (similar to 98%) at a very high nitrile conversion (similar to 95%). This work will also describe the effects of catalyst particle size and ammonia pressure on tallow nitrile hydrogenation. (c) 2006 Elsevier B.V. All rights reserved.