Highly Active and Stable Single-Atom Cobalt in Zeolite for Acetylene Semihydrogenation

Ethylene produced from steam cracking includes an acetylene impurity of 0.5–3%, harming the downstream polymerization process. To achieve polymer-grade ethylene, acetylene must be removed by chemoselective hydrogenation to ethylene without overhydrogenation to ethane. The current state-of-the-art process uses supported Pd nanoparticles (NPs) and toxic CO injections to poison the active sites, which is expensive and shows poor ethylene selectivity. To tackle this issue, the use of single-atom catalysts can offer a way to simultaneously improve selectivity through preferential desorption of ethylene over its hydrogenation and minimize cost. In particular, single-atom cobalt catalysis can address both of these issues. However, to date, single-atom cobalt has not been tested for this reaction. Herein, we present a cost-effective monometallic, cobalt-anchored zeolite Y (Co₁@Y) catalyst, synthesized via an in situ hydrothermal method, holding isolated active cobalt atoms that efficiently and selectively hydrogenate acetylene to ethylene. Characterization techniques proved the absence of NPs and the presence of single-atom cobalt sites. The catalyst achieved an ethylene selectivity of 90 ± 2% at full acetylene conversion, with a stable performance for over 400 h. Co₁@Y achieved TOF_ethylene greater than the previously reported zeolite-supported single-atom catalysts by ∼5 times. Varying the dispersion of cobalt from an NP to a single atom modified the reaction mechanism from associative to dissociative, remarkably improving catalytic activity and selectivity. This strategy can be extended to other relatively inactive metals and other hydrogenation reactions.