Selective Photocatalytic Reduction of Acetylene to Ethylene Powered by a Cobalt-Porphyrin Metal–Organic Framework

The production of polymer-grade ethylene requires the purification of the ethylene feed from acetylene contaminant. Accomplishing this task by state-of-the-art thermal hydrogenation requires high temperature, an external feed of H2 gas, and noble metal catalysts, and is not only expensive and energy-intensive but also prone to over-hydrogenation to ethane. This paper reports the photocatalytic semihydrogenation of acetylene to ethylene using the metal-organic framework (MOF) Co-PCN-222. Under pure acetylene atmosphere the system achieves an overall conversion of 1.6 mol g-1 Co, and remains catalytically active for one week. Under a mixed acetylene/ethylene atmosphere (1 vol.% acetylene, 30 vol.% ethylene, the industrially relevant conditions), the system achieves nearly 100% conversion of acetylene after 87 hours with >99.9% ethylene selectivity over ethane. The cobalt active species is contained within the Zr-based Co-PCN-222 framework and the heterogeneous nature of the MOF lends advantages over the homogeneous catalyst, namely facile recyclability and increased longevity. These features also offer substantial advantages over current thermocatalytic hydrogenation technologies with respect to selectivity and sustainability. While MOFs have been pursued academically for the physical separation of acetylene and ethylene, this is the first demonstration of the potential MOFs have as catalysts for the selective, photocatalytic conversion of acetylene to ethylene.