Enhanced toluene adsorption/desorption dynamic performances over modified USY zeolites after an aqueous ammonia treatment

Abstract

The dynamic adsorption/desorption performances of modified hierarchical USY zeolites treated with an ammonia solution (NH₄OH) at different concentrations were investigated using gas-phase toluene as an indicator. The characterization results indicated that the ammonia treatment could result in the expansion of microporous channels and the formation of a mesoporous structure without evident decrease in crystallinity. The experiment results regarding dynamic adsorption/desorption performances revealed that the mass transfer resistance of modified USY adsorbents were greatly reduced treating with NH₄OH. Among the modified samples, the 0.1 mol L⁻¹ NH₄OH treated USY adsorbent exhibited large adsorptive capacity and highest desorption rate, which show good cyclic performance that could preserve its adsorbent capacity after 20 cycles. In contrast, pristine USY samples had lost around 28% of the initial adsorption capacity after 20 cycles. Moreover, the NaOH-treated sample showed great crystallinity decline compared to the NH₄OH-treated samples due to excessive silicon atom leaching from the USY framework, and had lower adsorption capacity under humid conditions. Therefore, NH₄OH-modified USY zeolites could be promising adsorbents for the adsorption/desorption process of volatile organic compounds (VOCs).