Since the Industrial Revolution, most of our energy consumption has been originating from fossil fuels. However, the conventional air-blown combustion of fossil fuels results in the release of significant amounts of carbon dioxide into the atmosphere. This problem lead to the development of Carbon Capture and Storage (CCS) technologies as a solution, one of which is the oxy-fuel combustion which uses oxygen mixed with recirculated flue gas from the furnace. The bio-energy with carbon capture, utilization and storage (BECCUS) is reported as an effective carbon dioxide removal technology.

Therefore, to better understand the combustion process of biochar under oxy-fuel conditions, we work on the atomistic level modeling of biochar burnout in the project A7, "Atomistic Multiscale Simulation of Char Combustion", of the collaborative research center CRC/TRR 129 Oxyflame. We particularly aim to study reaction kinetics of biochar burnout reactions and the weak intermolecular interactions which affect the adsorption and diffusion processes.

To calculate reaction and activation energies, we use DFT/TPSS/SVP and/or DFT/TPSSh/TZVP methods and refine them with CCSD(F12*)(T) method and for larger systems using local correlation methods. For these, we use the programs dscf, ridft, jobex, DRC, woelfling, aoforce, ccsdf12, and pnoccsd. We also calculate the thermodynamic potentials of the stationaly points and the rate constants of the elementary reaction steps based on harmonic oscillator and rigid rotor approximation with a correction to the lower frequencies. For these, we are using the program freeh. The publications related to this work are the following:

• Multimethod modeling of H-Atom Abstraction

• CO Formation Mechanism

In order to improve the intermolecular potentials, we are also calculating adsorption potentials of the gases in the combustion medium such as O₂, CO, CO₂, CH₄, and H₂O. For this, we are using DFT/B3LYP/TZVP optimized structures, and CCSD(T) and PNO-CCSD(T) methods.