Influence mechanism of macropores on the room temperature desulfurization performance of ZnO/SiO2 adsorbent

Abstract

The coal chemical industry, as the main source of carbon emissions in China, will face great challenges under the constraints of the dual carbon goals. Coal derived gas deep desulfurization is an important component for highly efficient and clean utilization of coal, which is of great significance for carbon reduction. Zinc oxide is a commonly used adsorbent for desulfurization, but due to kinetic limitations, its room temperature desulfurization reactivity is very low, and this cannot meet the requirements of industrial application. Pore diffusion is a prerequisite for the reaction between ZnO and H2S, and is crucial for desulfurization performance. However, the influence of pore size, especially macropores, on the desulfurization performance and its mechanism have been rarely reported. For this reason, two ZnO/SiO2 adsorbents with mesopores and macropores in this study were prepared using a sol-gel method and a colloidal crystal template method, respectively, and the influence of macropores on their room temperature desulfurization performance was explored. It is found that although the introduction of macropores increases the specific surface area of the adsorbent, strengthens its surface alkalinity, improves the dispersion of ZnO, and increases the concentration of oxygen vacancies in the adsorbent, its introduction leads to a remarkable decrease in the desulfurization performance of adsorbent. The breakthrough sulfur capacity of mesoporous adsorbent is 151.9 mg/g, 2.3 times than that of macroporous adsorbent. This is because the macroporous structure is unstable and prone to collapse during the desulfurization process, which hinders the accessibility of reaction sites of ZnO; Secondly, the water vapor in the atmosphere is not conducive to the formation of a water film on the surface of macropores, thereby inhibiting the occurrence of desulfurization reactions. More importantly, the combustion of the template releases a large amount of heat during the preparation of macropores, which leads to a deep crosslinking of the SiO2 network and a decrease in the mesoporous pore size of adsorbent. The smaller mesoporous pore size results in an excessive amount of water physically adsorbed on its surface, inhibiting the reaction between ZnO and H2S.

Keywords

• zno/sio2 adsorbent
• macroporous structure
• room temperature desulfurization
• water film
• adsorbed water