Synthetic liquid fuels are ideal vectors for the distribution and storage of sustainable energy, allowing the exploitation of the actual infrastructure for fossil hydrocarbons. Such chemical energy carriers can be synthesised from recycled CO2 and H2 produced from intermittent renewable electrical power provided robust catalysts are developed.

A possible transformation pathway for CO2 consists in its hydrogenation to formic acid, which streamlines reversible hydrogen storage. However, the synthesis of formic acid remains defeated by unfavourable thermodynamics and intricate reactivities. In the scope of a cross-disciplinary project funded by SNF, the group of Prof. Rudolf von Rohr works, in collaboration with Professors Copéret, VandeVondele and Urakawa, on developing advanced catalytic materials and alternative reactive routes for the conversion of CO2 and H2 to formic acid and methanol in continuous flow microreactors (Figure 1).

We successfully implemented operando Raman microscopy to characterise the state of working heterogeneous catalysts and explore phase behaviour of the multi-component reactive mixture up to extreme operating conditions (500 bar, 400°C). Shedding light on fundamental mechanistic issues through the rational exploration of the reaction space led to a continuous two-reactor setup exploiting methyl formate as stable intermediate to alleviate the thermodynamic barrier of the direct synthesis. While methanol is obtained as valuable by-product, the trace amounts of formic acid and other derivatives of it demonstrate the potential of alternative processing routes for controlled CO2 conversion. The understanding of the physical and chemical equilibrium dynamics contributes to the rational design of improved catalysts for increased efficiency.

Figure 1: Schematics of the high-pressure microreaction setup for CO2 hydrogenation in flow with the analytical methods implemented for a rational design of catalysts and processes.

The team involved in this project include Helena Reymond, and Professor Rudolf von Rohr, ESC member and head of Transport Processes and Reactions Laboratory (LTR). Process engineering is mainly dealing with development and implementation of technical processes and plants that are able to change the state, the properties as well as the composition of a material. The focus is on design, operation, control and optimization of chemical, physical and biological processes. Moreover, also the importance of computer-based methods in process engineering is continuously increasing.

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