(37h) A DFT Study of SO2 Binding on CuO Oxygen Carrier Under Chemical Looping with Oxygen Uncoupling Conditions.

In the United States, roughly 1.7 million tons CO₂ per year is released from the electric power sector with coal being the largest CO₂ emission source¹. Among the various carbon capture and storage (CCS) technologies, chemical looping combustion (CLC) has recently gained positive interest because of its high CO₂ capture efficiency. A variant of CLC is chemical looping with oxygen uncoupling (CLOU) that is most suitable for solid fuel combustion. In CLOU, the fuel reacts with gas-phase oxygen released by the decomposition of a metal oxide (oxygen carrier) at suitable temperatures and oxygen partial pressures, unlike the CLC where the fuel reacts with the solid metal oxide to access the lattice oxygen. The sulfur compounds of fuel pose the risk of poisoning the oxygen carrier by reacting with the metal oxide; thus reducing its reactivity. One of the common oxygen carriers for CLOU is CuO combined with an inert support and CuO is known to be susceptible to sulfur poisoning. Some experimental studies have been conducted to investigate how sulfur compounds affect the oxygen carriers in CLOU process. However, first principle based theoretical studies to examine the interaction of SO₂ on oxygen carrier surface from atomic perspective is scarce.

Therefore, the purpose of this study is to theoretically investigate SO₂ binding on CuO and Cu₂O surfaces via combined density functional theory (DFT) and ab initio thermodynamics under CLOU conditions. In the fuel reactor of the CLOU process, CuO oxygen carrier exists in both CuO and Cu₂O forms while most of the fuel S compounds get oxidized to SO₂. Therefore, SO₂ binding on both CuO(111) and Cu₂O(111) surfaces have been studied at all possible surface active sites using different SO₂ molecular orientations. All DFT-based calculations have been performed using Vienna Ab Initio Simulation Package (VASP). The optimized configurations obtained from the calculations have been examined to identify active binding sites as well as the stable adsorption geometries of SO₂ molecule. The relevant density of states and charge transfer analysis have been conducted to understand the electronic interactions between the SO₂ molecule and CuO(111) and Cu₂O(111) surfaces. To relate the DFT-obtained results to experimental reaction conditions in approximation, ab initio thermodynamic calculations have also been performed and the stability of SO₂ bound surfaces at varying temperatures (up to 1000°C) and SO₂ partial pressures has been investigated.

1. U.S Energy Information Administration- Monthly Energy Review March 2019. Retrieved from https://www.eia.gov/totalenergy/data/browser/index.php?tbl=T12.06#/?f=M&...