Carbon dioxide (CO2) is a greenhouse gas that is significantly contributing to climate change. In tandem with advances in sequestering carbon, beneficial uses for CO2 are of high societal importance for developing a sustainable future. One attractive use of CO2 is its conversion to energy dense fuels (green energy vectors). One such fuel is methanol, made from CO2 via hydrogenation in conjunction with a multimetallic catalyst. The current best industrial (heterogeneous) catalyst incorporates copper and zinc-oxide nanoparticles with an alumina support. A special synergy is observed between the copper (active site) and zinc (reaction promoter), but these species and their connection is poorly defined and remains debated.
This project aims to isolate proximal copper and zinc centres, the fundamental building block for the construction of critical copper--zinc interfaces, within a well-defined, and highly tuneable ligand framework. Once isolated, the binding, activation and interconversion of key intermediates along the CO2-to-methanol hydrogenation pathway will be analysed.
The climate crisis is perhaps that biggest societal issue of our generation. Alarming trends were identified at the First World Climate Conference in 1979 in Geneva, and scientists from 50 nations agreed that urgent action was required to curb climate change. Since then, similar alarms have been made through the 1992 Rio Summit, the 1997 Kyoto Protocol, and the 2015 Paris Agreement. Yet greenhouse gas emissions continue to rise rapidly, with increasingly damaging effects on the Earth’s climate. In 2018 the Intergovernmental Panel on Climate Change (IPCC) stated “an immense increase of scale in endeavours to conserve out biosphere is needed to avoid untold suffering due to the climate crisis”. Despite over 40 years of global climate negotiations, with few exceptions, we have generally conducted business as usual and have largely failed to address this predicament.
The emission of CO2, one of the three most abundant greenhouse gases (along with methane and nitrous oxide) continues to rise, including an ominous spike in 2019. This, combined with other contributing factors, has led to increased surface temperatures, the disappearance of global ice, and increased ocean heat content, acidity and sea levels. Climate change is predicted to greatly affect marine, freshwater and terrestrial life, from plankton and corals to fishes and forests. Sequestering CO2 out of the atmosphere in useful forms is vitally important for the survival of life on Earth.
According to an IPCC special report, one of the most attractive uses of CO2 as a C1 feedstock is in the production of liquid fuels such as methanol. However, this process requires energy, and if this comes from fossil-fuel based electricity, there is no net reduction as the total CO2 generated during fuel synthesis tends to exceed the CO2 converted. The development of more efficient and selective catalysts for the conversion of CO2 to methanol will have far-reaching global benefits.
The overall objectives of the action were to use homogeneous organometallic molecules to model the reactions at the surface of the heterogeneous Cu/ZnO/Al2O3 catalyst. This was done through the design and investigation of new compounds that contain Cu and Zn in close proximity. These new Cu--Zn species were studied in reactions with key intermediates in CO2-to-methanol catalysis pathway.
In summary, the objectives of the proposal are as follows:
• Development of a series of ligands and associated Cu--Zn complexes, and their detailed characterisation that must include an understanding of the Cu--Zn interaction (work package 1).
• Build a detailed mechanistic picture of the potential steps in CO2 hydrogenation and an understanding of the role Cu--Zn cooperativity plays via stoichiometric reactivity and computational modelling (work package 2).
• As extension work, use the available Cu--Zn species and test for catalytic activity for direct CO2 hydrogenation with H2 to methanol (work package 3).
