Zinc inclusion to heterogeneous nickel catalysts reduces oligomerization during the semi-hydrogenation of acetylene

Isotopic labeling and density functional theory (DFT) were used to determine the mechanism for acetylene hydrogenation and oligomerization on well-defined intermetallic nickel-zinc catalysts. The primary benefit of adding zinc to nickel is a reduction in oligomeric species formation which leads to higher ethylene selectivity. The production of ethane is not highly dependent on zinc content; therefore, ethane production is not a good descriptor of ethylene selectivity since acetylene may also be converted to higher molecular weight products. Analysis using DFT and Langmuir-Hinshelwood kinetics shows that the large decrease in the adsorption energy of acetylene on intermetallic NiZn compared to pure Ni is responsible for the observed increase in ethylene selectivity. The adsorption energy of acetylene appears to be a descriptor for carbon-carbon bond formation since a high adsorption energy leads to an increased coverage of C₂ species and an increased rate of carbon-carbon bond formation.