Direct and selective hydrogenation of CO2 to ethylene and propene by bifunctional catalysts

Abstract

Reduction of CO₂ by H₂ produced from renewable electricity on a large scale would benefit both carbon recycling as well as H₂ storage and transport. Among the various CO₂ hydrogenation reaction products, light olefins, such as ethylene and propylene, are very important intermediates in the chemical industry. However, very efficient catalytic systems that are able to drive CO₂ hydrogenation reactions selectively to make olefins do not exist although the reactions are thermodynamically favorable. In this study, we demonstrated a selective hydrogenation process to directly convert CO₂ to light olefins via a bifunctional catalyst composed of a methanol synthesis (In₂O₃/ZrO₂) catalyst and a methanol-to-olefins (SAPO-34) catalyst. Under typical reaction conditions (e.g., 15 bar, 400 °C, and a space velocity of 12 L g_cat⁻¹ h⁻¹), light olefins (ethylene and propylene) with a selectivity of 80–90% in hydrocarbons can be obtained with a CO₂ conversion of ∼20%. To the best of our knowledge, this is the highest selectivity reported to date, which significantly surpasses the value obtained over conventional iron or cobalt CO₂ Fischer–Tropsch synthesis catalysts (typically less than 50%). Moreover, our designed bifunctional catalyst shows good catalytic stability and can run for 50 h continuously without obvious activity decay. Our study provides an important contribution for CO₂ conversion to value-added chemicals.