There is an increase in the utilization of renewable electricity to deter climate change. Electrochemistry offers novel processes to decarbonize the chemical industry by directly utilizing renewable electricity to convert renewable feedstocks into fuels and chemicals. Additionally, electrochemical systems are amenable for small scale processing as they operate at near atmospheric pressure and temperature. This makes them a more sustainable technology for distributed manufacturing operation.

We evaluate the use of Ru-, IrO₂-, and Pt-based heterogeneous catalysts for the electrocatalytic oxidation (ECO) of organic molecules derived from biomass such as carboxylic acids into fuels and chemicals. Our results show that carboxylic acids such as valeric acid can be electrochemically decarboxylated (ECDX) into paraffins, olefins, and alcohols via the Kolbe and non-Kolbe mechanisms. The obtained decarboxylation rates (TOFs) of the electrochemical route at room temperature and atmospheric pressure is one order of magnitude higher than the TOF of thermocatalytic decarboxylation at 300 °C and 37 bar.^1-3 The ECDX activity, product selectivity, and current efficiency depend on operation potential and anode composition, Figure 1. Increasing the applied potential improves the rates of ECDX and oxygen evolution (OER), changing the current efficiency. Additionally, the product selectivity also changes with applied potential and electrode composition. We also found that the ECDX performance depends on the metal particle size and composition. Pt foil was active for ECDX but Pt nanoparticles were only active for OER. However, RuO₂ nanoparticles had higher ECDX activity than RuO₂ thin film (TF) while preserving the product selectivity.⁴ We demonstrated this technology using real biomass-derived feedstocks and showed decarboxylation of carboxylic acids present in bio-oil as well as wastewater while simultaneously generating H₂.⁵

References

1. Qiu, Y.; Lopez-Ruiz, J. A.; Sanyal, U.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Anodic electrocatalytic conversion of carboxylic acids on thin films of RuO2, IrO2, and Pt. Appl. Catal. B-Environ. 2020, 277, 119277, DOI 10.1016/j.apcatb.2020.119277.
2. Lopez-Ruiz, J. A.; Pham, H. N.; Datye, A. K.; Davis, R. J., Reactivity and stability of supported Pd nanoparticles during the liquid-phase and gas-phase decarbonylation of heptanoic acid. Appl. Catal. A-Gen. 2015, 504, 295-307.
3. Lopez-Ruiz, J. A.; Davis, R. J., Decarbonylation of heptanoic acid over carbon-supported platinum nanoparticles. Green Chemistry 2014, 16 (2), 683-694, DOI 10.1039/c3gc41287c.
4. Qiu, Y.; Lopez-Ruiz, J. A.; Zhu, G.; Engelhard, M. H.; Gutiérrez-Tinoco, O. Y.; Holladay, J. D., Electrocatalytic decarboxylation of carboxylic acids over RuO2 and Pt nanoparticles. Appl. Catal. B-Environ. 2021, In Submission.
5. Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. J. Appl. Electrochem. 2021, 51 (1), 107-118, DOI 10.1007/s10800-020-01452-x.