(6ix) Low temperature carbon dioxide reduction to carbon monoxide on perovskite-type oxides

Authors: 
Daza, Y., University of South Florida
Kuhn, J., University of South Florida

In the US, around 6000 million mega tonnes of CO2 are released yearly to the atmosphere, yet less than 300 mega tonnes are re-utilized in industrial processes such as urea and salicylic acid synthesis. Here, an alternative to CO2 utilization is proposed, where CO2 can be transformed to high-value chemicals that could be used as a source of C1 chemistry for synthetic fuels synthesis.  Being a very stable molecule, CO2 requires extreme conditions (very high temperatures or reducing environments) for its activation. The reverse water gas shift (RWGS) reaction can convert CO2 to CO at ~ 600 °C but requires excess hydrogen, is equilibrium limited and commonly produces undesired CH4. In spite of its disadvantages, it is cost competitive and the incorporation of renewable energy has been proven promising [1].

In this work, the Reverse Water Gas Shift Chemical Looping (RWGS-CL) process is demonstrated [2,3,4]. Here, the RWGS is intensified to avoid its most common drawbacks (use of excess hydrogen, equilibrium limitations and side reactions) using mixed oxides with high oxygen mobility. The process consists on a hydrogen pulse, which creates oxygen vacancies in the materials that are later re-oxidized by a flow of carbon dioxide, while yielding CO [2,3,4].

Perovskites (ABO3) are ideal for RWGS-CL because they have the ability to form oxygen vacancies while maintaining their crystalline structure and their catalytic properties can be tailored by partial substitution of the A and B site metals. Various concentrations of lanthanum and strontium [2], and cobalt and iron [3] were tested in the A and B site of the perovskite respectively to design a process that allows maximum CO formation, at the lowest temperatures whit high CO yields. The tested materials proved stable during the five cycles studied.

The RWGS-CL process transforms CO2 to CO starting at 500 °C (~100 °C lower than conventional RWGS) [3], which could allow for a temperature integration of the process for CO2 conversion and fuels synthesis through Fischer-Tropsch, lowering overall energy use and environmental impact if heat is provided by renewable sources.

References

[1] Mallapragada, D. S.; Singh, N. R.; Curteanu, V.; Agrawal, R. Sun-to-Fuel Assessment of Routes for Fixing CO2 as Liquid Fuel. Ind. Eng. Chem. Res. 2013, 52, 51365144.

[2] Daza, Y.A., Kent, R.A., Yung, M.M., Kuhn, J.N., Carbon dioxide conversion by reverse water gas shift chemical looping on perovskite-type oxides. Ind. Eng. Chem. Res. 2014, 53, 58285837.

[3] Daza, Y.A., Maiti, D., Kent, R.A., Bhethanabotla, V.R., Kuhn, J.N., Isothermal reverse water gas shift chemical looping on La0.75Sr0.25Co(1-Y)FeYO3 perovskite-type oxides. In press Catalysis Today, 2015.

[4] Daza, Y.A., Maiti, D., Hare, B.J., Bhethanabotla, V.R., Kuhn, J.N., More Cu, more problems: Decreased CO2 conversion ability by Cu-doped La0.75Sr0.25FeO3 reduced perovskite oxides. Submitted to Surface Science for a special issue honoring Gabor Somorjai.