Simultaneous CO2 reduction and CH4 oxidation to fuels in a flow cell using MOx as catalysts

• Grant number: 22/16560-4
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)
• Start date: April 01, 2023
• End date: March 31, 2024
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Physical-Chemistry
• Principal Investigator: Cauê Ribeiro de Oliveira
• Grantee: Eduardo Henrique Dias
• Supervisor: Cao Thang Dinh
• Host Institution: Instituto de Química de São Carlos (IQSC). Universidade de São Paulo (USP). São Carlos , SP, Brazil
• Institution abroad: Queen's University, Canada
• Associated to the scholarship: 19/10689-2 - Preparation of reaction systems for photocatalytic methane-to-methanol selective oxidation, BP.DD

Abstract

Due to the high consumption of fossil fuels, many technologies have been developed to improve the transformation of gases such as CO2 and CH4, trying to reduce the greenhouse effect caused by them and, at the same time, profiting from the formed products. Electrochemical systems have an enormous potential to transform CO2 and CH4 into various chemicals, adaptable due to the different types of electrochemical cells that can be developed. In addition, it is a versatile system that can be applied under various temperature and pressure conditions. These systems are evaluated by metrics such as current density, Faradaic, and energy efficiency, conversion, and system stability. To achieve higher values for each parameter, the utilization of suitable catalysts and well-defined systems is essential. Several catalysts have been studied, with Copper and its oxides among the best catalysts for CO2 reduction. Other catalysts such as MnO2, NiO, and Co3O4 have shown promising results for CH4 oxidation, but under conditions of high temperatures and pressure. CO2 reduction and CH4 oxidation in aqueous solution display similar barriers to be overcome. Both gases are low-soluble in water. CO2, for example, has a solubility of 30 mM in water[2] (at 1 bar and 25 °C), limiting the conversion rate. Another point is the high energy needed to activate these molecules. In the CO2 molecule, the carbon atom is strongly bonded with oxygen atoms by double bonds (bond energy 806 kJ.mol-1). In comparison, CH4 presents four C-H bonds with dissociation energy of 439.4 kJ.mol1, perfect tetrahedral geometry, and low polarizability. As a result of these facts, it is necessary to find a catalyst that displays good interactions with the gases, decreases the activation energy, or produces active species that will reduce/oxidize the CO2/CH4. In this context, the previous achievements of FAPESP process No. 2019/10689-2 using H-cells indicated that C/CuO cathode is efficient for CO2 reduction, while C/MnO2 anode can control CH4 to methanol. Therefore, in this project, we propose to assemble in a single device the CO2 reduction and controlled oxidation of CH4, simultaneously, under the guidance of Prof. Dr. Cao Thang Dihn, and using the previously developed materials. His supervision is essential to the success of this proposal, given his knowledge of continuous CO2 reduction devices with high current density. These results depend on a deeper understanding of electrochemical cell engineering and process evaluation. The coupling of both processes can potentially reduce the net energy for CO2 reduction (due to the lower potential for CH4 oxidation), providing an alternative utilization for CH4 in the chemical industry, avoiding burning it. Thus, the execution of this BEPE proposal will be strongly connected to the FAPESP process mentioned above, providing resources for developing effective electrochemical systems. The catalysts will be synthesized by solvothermal methods and applied in an electrochemical flow system at different potentials and flow rates for setup optimization. Advanced characterization techniques such as XRD, N2 physisorption, SEM-FEG, and TEM will be employed to support the studies of the catalysts. Techniques such as XPS and FTIR will be carried out to understand kinetic reactions of products. (AU)