Synthesis of supported Ni catalysts by atomic layer deposition

Nickel nanoparticles grown on an Al2O3 support by atomic layer deposition (ALD) had higher selectivity for propylene hydrogenolysis. The Ni was deposited in a fluidized bed reactor with bis(cyclopentyldienyl)Ni and H2 reactants. Varying the number of ALD cycles varied the Ni loading between 4.7–16.8 wt.% and the average Ni particle diameters between 2.4 and 3.3 nm. The number of surface sites per gram of Ni, determined from CO TPD, was at least five times higher on ALD-prepared catalysts than typical Ni/Al2O3 catalysts prepared by incipient wetness impregnation. The fraction of CO desorbed from steps and kinks on the ALD-prepared catalysts was at least three times higher. Correspondingly, the selectivity for propylene hydrogenolysis, instead of hydrogenation, was above 10% on an ALD-prepared catalyst but below 0.4% on the incipient wetness catalyst. Preparing catalysts by ALD appeared to increase the step and kink site density and thus increase hydrogenolysis selectivity.