Photocatalytic Hydrogenation of Acetylene to Ethylene on a Semiconductor Quantum Dot Catalyst

This thesis describes the design, synthesis, and characterization of heavy metal-free copper indium sulfide/zinc sulfide core/shell quantum dots (CuInS2/ZnS QDs) and their use as photo-redox catalyst for the semi-hydrogenation of acetylene to ethylene. Ethylene, one of the world’s most important commodity chemicals, is the starting material in the production of ~60% of all plastics. Almost 200 million tons of crude ethylene are produced every year through steam cracking, which unavoidably introduces 0.5 − 2 vol% acetylene impurities. Acetylene is a poison for the catalysts used for ethylene polymerization and therefore it needs to be removed to obtain polymer-grade ethylene. The state-of-the-art process for purifying crude ethylene is the thermocatalytic hydrogenation of acetylene to ethylene. Despite being a well-established industrial technology, it suffers from several drawbacks, including the need of (i) a H2 feed, (ii) high temperature and pressure, and (iii) a noble metal catalyst prone to overhydrogenation to ethane. This research experimentally realizes an all-in-one photocatalyst based on CuInS2/ZnS quantum dots that achieves ≥99.9% selective, visible-light powered and catalytic conversion of acetylene to ethylene under both competitive (ethylene co-feed) and non-competitive (pure acetylene, no ethylene co-feed) conditions. The reported system operates at room temperature and uses water as hydrogen source, thus offering a sustainable and economical route for this industrially relevant reaction with substantial advantages over the present energy-intensive hydrogenation technology.