(81c) Mechanistic Analysis of the Selective Hydrogenation of Acetylene and Crotonaldehyde Over NiZn

Selective catalytic hydrogenation of alkynes and conjugated aldehydes is useful in both the production of plastics and in organic synthesis. Ethylene produced via steam cracking is contaminated by a small amount of acetylene which poisons ethylene polymerization catalysts in the production of polyethylene. Current technology uses precious metal catalysts such as modified palladium to purify this stream through selective hydrogenation of acetylene. This process can be costly due to the necessity of precious metal catalysts. Likewise, the selective hydrogenation of α-β unsaturated aldehydes for flavor and perfume syntheses is costly and often wasteful due to the necessity of similar precious metal catalysts or stoichiometric conversion reactions. Experimentally, NiZn nanoparticles are a non-precious alternative selective hydrogenation catalyst for both of these reactions. To more fully understand the reasons for this selectivity and potentially guide the search for additional non-precious catalysts, DFT was used to investigate the mechanistic origin of selectivity in both acetylene hydrogenation and α-β unsaturated aldehyde hydrogenation. DFT energetics are used with a kinetic model to examine possible explanations of observed experimental selectivities.