Ethylene from hydrogen and carbon dioxide

An international research group has developed a new photocatalytic process for hydrogen activation that can be used to produce ethylene from CO2 and hydrogen. The international research team comprises Professor Paolo Fornasiero from the Department of Chemical and Pharmaceutical Sciences at the University of Trieste, affiliated with the Institute of Chemistry of Organometallic Compounds (ICCOM-CNR) in Florence and member of the National Interuniversity Consortium for Materials Science and Technology (INSTM), and Nenchao Luo and Feng Wang from the Dalian Institute of Chemical Physics (China). The research has been published in the scientific journal Science and could have significant industrial and environmental applications. Ethylene is a fundamental component in the production of plastics used across various sectors, with annual production exceeding 150 million tonnes and currently based on the catalytic transformation of fossil hydrocarbons, a process that generates greenhouse gas emissions into the atmosphere.

The research proposes a new method of activating hydrogen, or more simply, making it more reactive and ready to form new chemical bonds through the formation of electric dipoles induced by ultraviolet radiation on the surface of gold-based photocatalysts deposited on titanium dioxide. The discovery has been applied to the carbon dioxide hydrogenation reaction with the aim of transforming this greenhouse pollutant into high-value-added products. The research stems from awareness of the future availability of green hydrogen that could be produced in large quantities through electrolysis using electricity from renewable sources. The overall photocatalytic process achieved leads to the selective formation of ethylene from carbon dioxide and hydrogen. "In the perspective of an increasingly sustainable, less polluting and energy-intensive economy, our study suggests the possibility of producing ethylene with an innovative and sustainable method, drastically reducing dependence on fossil sources, decoupling its cost from raw material and energy prices, particularly oil and natural gas," stated Paolo Fornasiero.

Ethylene is currently produced through a catalytic cracking process of hydrocarbons in the presence of steam. This process involves heating hydrocarbons, such as ethane, propane, naphtha and gas oils, to high temperatures (typically 750-950°C) with steam. The steam helps reduce the undesired formation of carbonaceous deposits on catalyst surfaces and is involved in the reaction of breaking down larger hydrocarbons into smaller hydrocarbons, including ethylene. The resulting mixture is then separated through compression and distillation to isolate ethylene. Production costs are heavily dependent on the type of hydrocarbon used and its local availability, to which must be added aspects related to transport difficulties and competing demands for energy use. The possibility of using carbon dioxide and green hydrogen, light and an appropriate photocatalyst to produce ethylene could therefore bring not only economic and environmental advantages, but also reduce increasingly critical dependencies on raw materials that are not uniformly distributed. The researchers have been able to successfully apply the results under conditions close to those of industrial interest, creating a first prototype.