Experimental and density functional study of sulfur trioxide formation catalyzed by hematite in pressure oxy-combustion

Pressurized oxy-combustion is one of the most promising carbon capture technologies which could reduce global CO₂ emission. SO₃ is one of the main conventional pollutants and might be produced in large concentration in pressurized oxy-combustion than air combustion, posing risks to the environment and safe operation of boiler. However, no research has been conducted on SO₃ catalytic formation in pressurized oxy-combustion, despite the fact that SO₃ heterogeneous formation accelerated by hematite is more significant than homogeneous formation. Consequently, it is critical to understand SO₃ catalytic formation in pressurized oxy-combustion. In this study, SO₃ homogeneous and heterogeneous formation catalyzed by hematite were explored at 1 bar and 4 bar in a pressured fixed bed reactor. Temperature, pressure, and the addition of NO were discussed in this study. Density functional study method was employed to further elucidate the hematite catalysis mechanism. The findings show that hematite can catalyze the SO₃ formation, but the catalytic effect weakens at high pressure. The inclusion of NO could enhance SO₃ catalytic formation. Density functional study indicated that changing the main gas from N₂ to CO₂ has little impact on SO₂ and O₂ adsorption and subsequent SO₃ production. SO₃ adsorption becomes more stable with increasing O atom coverage, making SO₃ desorption more difficult. Since NO has a lower adsorption energy than SO₂ and O₂, it has less effect on catalysis, however, NO₂ formation could act as a strong catalyst and can enhance SO₃ formation. This study could provide a better understanding of how the atmosphere and pressure influence SO₃ heterogenous formation in pressured oxy-combustion.