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

Abstract

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.