(231a) Atomic Layer Deposition As a Catalyst Synthesis Technique for Nickel Nanoparticles

Efforts to design new catalysts for renewable energy applications have revolved around increasing selectivity & activity by exploring advantages of catalysis at the nanoscale, mainly due to geometric & electronic effects created by nanostructures or bimetallic structures.  This work investigates the synthesis of Ni nanoparticle catalysts through the scalable gas phase synthesis route of Atomic Layer Deposition (ALD).  Typically ALD deposits Ni as a NiO film when using oxygen as the secondary precursor. However; by using hydrogen as the secondary precursor, metallic Ni nanoparticles were synthesized with particle diameters of 2 nm with 1 ALD cycle.  The size of the nanoparticles can be increased by performing more ALD cycles to give the ALD synthesis an element of particle size control.  The catalysts were characterized via chemisorption, temperature programmed desorption (TPD), transmission electron microscopy (TEM), inductively coupled plasmon mass spectroscopy (ICP-MS), energy dispersive x-ray spectroscopy (EDS) & compared to traditional incipient wetness Ni catalysts.  The incipient wetness Ni catalysts were also used as a base comparison of catalytic activity for alkene hydrogenolysis reactions using propylene as a probe reactant molecule.  Hydrogenation turnover frequencies were at least one order of magnitude higher for the nanoscale ALD catalysts than the incipient wetness catalysts.  In tuning the size of the nanoparticles, certain sized nanoparticles were found to have hydrogenolysis activity in addition to the typical hydrogenation.  To further explore the benefits of Ni ALD, bimetallic ALD catalyst nanoparticles were investigated for a NiPt bimetallic system.  Pt ALD has been an established technique for creating Pt nanparticles.  However, by combining the novel Ni ALD with Pt ALD, nanoscale bimetallic catalysts were created.  To address issues of specific Pt deposition on Ni particles, temperature programmed reduction (TPR) and chemisorptions were used to characterize the Ni & Pt depositions separately and together to determine the extent of bimetallic interaction.