Zinc Based High Temperature Methanol Synthesis Catalysts Enabling Direct Synthesis of Olefins and Aromatics from CO₂

It has been estimated that 302 million tons of plastic waste were generated worldwide in 2015 [1]. Unfortunately, there is still a need for burning plastic waste to avoid it being disposed on landfills where no value of the products is regained. When incinerating a plastic product, the fraction of the energy that went into producing the plastic can be recovered as electricity and heat. Closing the carbon loop from plastic incineration by capturing and recycling CO₂ to produce new plastic will minimize the climate impact of the current emissions and reduce the need for fossil resources in plastic production. Promoted Fisher-Tropsch catalysts can convert CO₂ and H₂ into ethylene and propylene with yields up to 60% [2]. This yield is close to the theoretical limit by the Anderson-Schulz-Flory distribution, which is still considered to be a limitation for the Fisher-Tropsch process. An alternative route for converting CO₂ into hydrocarbon products is the  combination of methanol synthesis and the methanol to hydrocarbon reaction. The methanol synthesis is equilibrium limited and a strategy to overcome this is to combine a methanol synthesis catalyst with a zeolite catalyst within one reactor [3,4]. In the temperature range of 300 to 420 °C, necessary for the zeolite to be active, the traditional Cu/ZnO/Al₂O₃ methanol synthesis catalyst cannot be used. At these temperatures, severe sintering of the metallic copper deactivates the catalyst. Furthermore, the hydrogen spill-over effect for the metallic copper results in the hydrogenation of the olefins formed in the zeolite [5]. To overcome these limitations, metal oxides capable of converting CO2 and H2 to methanol at relatively high temperatures have been synthesized and tested.