Supporting renewable fuel production with Citric Acid

As the demand for energy continues to increase, clean energy sources remain in the minority and environmental regulations become stricter. There is now a greater interest in transitioning to sustainable energy sources and promoting decarbonisation than ever before. While most sectors can easily switch to using electricity produced from renewable and carbon-free sources, the aviation and maritime sectors are struggling to find a solution due to similar sustainability policies.

One of the most promising solutions for the coming decades is the production of synthetic liquid fuels through the hydrogenation of CO₂, which allows for close to net zero-carbon emissions. However, CO₂ hydrogenation faces challenges due to the extreme inertness of CO₂, the high C–C coupling barrier, and competing reactions, resulting in low conversion rates and a lack of specificity. As a result, much research is focused on catalysts, which are crucial for the reaction (Figure 1). Citric acid is often used to improve the structural properties of catalysts. Catalysts modified with citric acid typically exhibit better stability and more reaction sites, leading to superior performance compared to untreated catalysts. This significantly increases the yield and reduces waste in the production process of CO₂-derived synthetic fuels.

There are various methods for preparing catalysts using citric acid. Citric acid is commonly used as the organic compound in the “sol-gel” method. By incorporating the organic matrix, the active sites are evenly dispersed and numerous, resulting in a smaller crystallite size and larger surface area. In ternary or quaternary systems, the matrix also ensures that the different metals remain mixed on an atomic scale¹.

For example, methanol is a promising alternative to fossil fuels in maritime transport. Researchers have used three different synthesis methods to prepare Mo₂C and Cu–Mo₂C catalysts for the hydrogenation of CO₂ to methanol. These methods include solid state synthesis, solvothermal synthesis, and sol-gel auto-combustion. The Cu–Mo₂C catalyst production from sol-gel auto-combustion uses citric acid as a combustion agent. This method has performed best for the CO₂ conversion and provided the highest selectivity towards methanol. This is attributed to the higher number of CO₂ and H₂ activation sites in the catalyst produced by the sol-gel auto-combustion method using citric acid². Other approaches have also demonstrated that catalysts treated with citric acid are most effective in synthesising methanol^3,4.

Another study has shown that jet fuel can be produced from CO₂ using an Fe-Mn-K catalyst. The effectiveness of the catalyst in converting CO₂ was significantly improved when prepared with citric acid as an organic compound⁵.

Methane, another viable fuel option, can be generated for various applications. Researchers have successfully enhanced CO₂ hydrogenation to produce methane by using an improved xCA-Ni/Y2O3 catalyst. The catalyst’s efficiency was also improved by adding citric acid during the preparation process⁶.

Jungbunzlauer offers citric acid in both monohydrate and anhydrous​​​​​​​ forms, which is already widely used in industries such as food and beverages, pharmaceuticals, cleaning agents, and construction and chemical industries. What sets Jungbunzlauer’s citric acid apart is not only its superior quality and service, but also its competitively low and continuously decreasing product carbon footprint. Jungbunzlauer is committed to reducing energy consumption and implementing decarbonisation technologies in its production sites.

For more information on Jungbunzlauer’s products and decarbonisation projects, visit https://www.jungbunzlauer.com/en/sustainability.

Figure 1: With the appropriate catalyst, CO₂ and H₂ can be used to synthesise single- and higher-carbon products.

References

^{1 Danks, A. E., Hallb, S. R. und Schnepp, Z. The evolution of ‘sol–gel’ chemistry as a technique for materials synthesis. Mater. Horiz. 2016, S. 91-112.
2 Heracleous, E., Koidiab, V. und Lappasa, A. A. CO2 conversion over Cu–Mo2C catalysts: effect of the Cu promoter and preparation method. Catal. Sci. Technol. 2021, S. 1467–1480.
3 Peng, L., et al. Preparation of Cu-based Catalyst by Solid-phase Grinding Method with Citric Acid Assisting and Performance Research in Methanol Synthesis Reaction from CO2 Hydrogenation. Journal of Molecular Catalysis(China). 2017, S. 141-151.
4 Malik, A. S., et al. Development of highly selective PdZn/CeO2 and Ca-doped PdZn/CeO2 catalysts for methanol synthesis from CO2 hydrogenation. Applied Catalysis A: General. 2018, S. 42-53.
5 Yao, B., et al. Transforming carbon dioxide into jet fuel using an organic combustion-synthesized Fe-Mn-K catalyst. Nat Commun. 2020.
6 Li, Y., et al. Remarkably efficient and stable Ni/Y2O3 catalysts for CO2 methanation: Effect of citric acid addition. Applied Catalysis B: Environmental. 2021.}