Unraveling the capture mechanism of gaseous AsO over H-ZSM-5 zeolite from coal-fired flue gas: Experimental and theoretical insights.

Gaseous AsO discharged from coal-fired power plants results in severe detriments to the ecological environment. It is of great urgency to develop highly efficient AsO capture technology for reducing atmospheric arsenic contamination. Utilizing solid sorbents for gaseous AsO capture is a promising treatment for AsO capture. The zeolite of H-ZSM-5 was applied for AsO capture at high temperatures of 500-900 °C. Special attention was paid to clarifying its capture mechanism and identifying the influence of flue gas components via density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. Results revealed that due to high thermal stability with large specific areas, H-ZSM-5 demonstrated excellent arsenic capture at 500-900 °C. The captured arsenic consisted of As and As speciations, ascribed to AsO adsorption and oxidation. Moreover, As and As compounds were both through physisorption or chemisorption at 500-600 °C while dominant chemisorption at 700-900 °C. In particular, As compounds were much more steadily fixed in products at all operating temperatures. Combining the characterization analysis and DFT calculations, it further verified that both Si-OH-Al groups and external Al species of H-ZSM-5 could chemisorb AsO, and the latter exhibited much stronger affinities via orbital hybridization and electron transfer. The introduced O could facilitate AsO oxidation and fixation in H-ZSM-5, especially at a lower concentration of 2%. Additionally, H-ZSM-5 possessed great acid gas resistance for AsO capture under the concentration of NO or SO less than 500 ppm. AIMD simulations further identified that compared to NO and SO, AsO was far more competitive and occupied the active sites of the Si-OH-Al groups and external Al species of H-ZSM-5. Overall, it demonstrated that H-ZSM-5 is a promising sorbent for AsO capture from coal-fired flue gas.