CO₂ hydrogenation

The conversion of waste CO₂ into value-added chemicals via CO₂ hydrogenation is a promising carbon utilization strategy.

Carbon capture, usage and storage are key tools that many governments have committed to adopting in response to the rise in atmospheric CO₂ levels¹. Although challenging because of its high thermochemical stability, the chemical transformation of captured CO₂ can mitigate anthropogenic CO₂ emissions into the atmosphere and produce valuable small molecule building blocks and fuels.

Credit: Springer Nature Limited

CO₂ hydrogenation is a crucial catalytic CO₂ conversion reaction, where CO₂ and renewably sourced H₂ are combined to synthesize a variety of C₁ and C₂₊ products depending on the reaction conditions and catalyst used². CO₂ hydrogenation can be achieved thermo-, photo- or electrocatalytically, with thermocatalytic CO₂ hydrogenation being the most mature technology.

When examining small molecule synthesis and CO₂ hydrogenation, there are two aspects which should be considered: the products themselves, but also the synthesis of the catalyst. Achieving high product synthesis rates, selectivity and reaction stability are important considerations for catalytic reaction design — low synthesis rates mean the processes cannot compete with other production methods, such as the cracking of oil. Low selectivity necessitates additional steps to purify reaction products, and low reaction stability leads to short reaction lifetimes³. Understanding why reactions are high performing is key, and this knowledge should be linked back to the reaction conditions and the catalyst.

Additionally, the synthesis of new catalysts using interesting methods may have unusual effects upon the CO₂ hydrogenation reaction. Different catalysts can influence the reaction pathways taken, and this then influences the oxidation level and chain length of the resulting products². Catalyst engineering is also important, and catalysts with the same composition can give different product selectivity depending on sizes, orientations or crystal structure.

Thermocatalytic CO₂ hydrogenation is discussed in a Review in this issue. Fan, Feng, Sun, Liu and co-workers examine the influence of catalyst design on the selectivity of CO₂ hydrogenation reactions. The Review also discusses how catalyst design should consider metal selection, promotor addition and support interactions to control the reduction product which is synthesized. Furthermore, it is suggested that product selectivity is the major challenge when valorizing CO₂, and that the catalyst is the key to controlling this selectivity.

At Nature Synthesis, when papers are assessed editorially on the topic of CO₂ hydrogenation and heterogeneous catalysis more widely, we keep the following factors in mind: has the catalyst been made in an interesting way, or is the catalyst a new material? How has the catalyst influenced the reaction and is the mechanism fully described? Is the catalytic outcome linked to the catalyst using robust characterization, including experimental or computational methods? Or, has a routine method or catalyst been modified, giving rise to exceptional catalytic metrics and how is this enhanced performance rationalized? The processing steps of catalysts can influence the outcome of the catalytic reaction, and we encourage manuscripts that acknowledge this. We encourage authors to carefully check the standard methods of reporting catalytic metrics in the field in which they are publishing, and to use standard units. Comparison tables of relevant literature should be included in the supplementary information. Additionally, it is helpful for reviewers and readers if the methods of calculating your catalytic metrics, such as rates and stabilities, are included in the Methods section.

Increased commitments for carbon capture and utilization provide growing interest in thermocatalytic CO₂ hydrogenation, which is a promising tool for waste CO₂ valorization. The success of small molecule synthesis via CO₂ hydrogenation routes is dependent on the design and synthesis of highly-active and selective catalysts, which are stable under the reaction conditions used.