Multiple Cuprous Centers Supported on a Titanium-Based Metal–Organic Framework Catalyze CO₂ Hydrogenation to Ethylene

Hydrogenation of carbon dioxide (CO₂) to ethylene (C₂H₄) can be achieved in two routes via tandem reactions: (1) CO₂ hydrogenation to methanol (CH₃OH) followed by methanol-to-olefin conversion and (2) reverse water-gas shift reaction followed by Fischer–Tropsch synthesis. Here we present another tandem route for CO₂-to-C₂H₄ conversion via (3) CO₂ hydrogenation to ethanol (C₂H₅OH) followed by C₂H₅OH dehydration. Multiple cuprous (Cu^I) centers were loaded onto the Ti₈(μ₂-O)₈(μ₂-OH)₄ secondary building units of a Ti-based metal–organic framework (MOF), MIL-125-NH₂, via deprotonation and ion exchange of the μ₂-OH groups. These multiple Cu^I centers catalyzed CO₂ hydrogenation to C₂H₅OH, while the Ti₂-μ₂-O^–M⁺ (M⁺ = H⁺, Li⁺) sites converted C₂H₅OH to C₂H₄. The MOF achieved CO₂-to-C₂H₄ generation rates of up to 2598 μmol g_Cat^–1 h^–1 in supercritical CO₂ (CO₂ 30 MPa, H₂ 5 MPa) at 85 °C and 514 μmol g_Cat^–1 h^–1 in the gas phase at 5 MPa (H₂:CO₂ = 3) and 100 °C, respectively. This work opens another path to selectively producing C₂H₄ via the hydrogenation of CO₂.