Theoretical study on the adsorption and removal of quinoline from simulated fuel by modified NaY zeolite

A large amount of nitrogen oxides in the atmosphere posed a serious threat to the environment and the health of animals and plants. Nitrogen compounds in diesel were one of the main sources of nitrogen oxides in the atmosphere. Adsorption denitrification technology had attracted widespread attention because it could efficiently remove nitrogen compounds from diesel under mild conditions. NaY zeolite had been widely used in the petroleum field due to its excellent cation exchange capacity and selectivity. In response to national environmental protection policies and to meet increasingly stringent diesel quality standards, our research group successfully prepared AgY, CuY, ZnY, and CrY zeolites by replacing transition metal ions Ag⁺, Cu²⁺, Zn²⁺, and Cr³⁺ with the compensating cation Na⁺ on NaY zeolite through ion exchange method based on the cation exchange characteristics of NaY zeolite. This further improved the adsorption effect of Y zeolite on nitrogen compounds in diesel. AgY, CuY, ZnY, CrY, and NaY were characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), and were used for adsorption and removal of quinoline from simulated fuel. The experimental results showed that the XRD patterns of the modified zeolite exhibited characteristic peaks of Y-shaped zeolite, and the lattice constants decreased slightly; The FT-IR spectrum of AgY, CuY, and ZnY zeolites showed a red shift at the 1024 cm⁻¹ absorption peak, and a blue shift for CrY. The changes in the lattice constants and the absorption peaks of the FT-IR spectrum indirectly indicated that the transition metal ions were successfully replaced with Na⁺ on the zeolite framework. It was AgY>CrY>CuY>ZnY about the adsorption capacity of AgY, CuY, ZnY and CrY for quinoline, the adsorption capacity of four zeolites was significantly higher than that of NaY zeolite. In order to better study the nitrogen removal mechanism of zeolite adsorption at the micro molecular level, materials studio simulation software was used to calculate the relevant parameters. The XRD patterns of five zeolites were drawn by simulation calculation, and the 2θ error between the simulated and experimentally measured XRD spectra was less than 0.1°, which verified the rationality of the unit cell model; In order to improve the calculation efficiency, the S_Ⅱ site in the unit cell was used as the reactive active site, and the 12T cluster was intercepted instead of the whole for subsequent theoretical calculation. The absorption peak of modified Y zeolite at 1147 cm⁻¹ of the antisymmetric stretching vibration of the double six membered ring between the attributed tetrahedrons disappears or strengthens, indicating that the compensation ions on the six membered ring had been replaced by transition metal ions, affecting the original vibration frequency of the six membered ring. The change of this peak further verified the rationality of the selection of the 12T cluster model. Based on density functional theory (DFT), adsorption parameters such as adsorption energy, electrostatic potential, ESP charge difference, and Mulliken population analysis of quinoline on 12T clusters of five zeolites were simulated and calculated. The order of absolute values of adsorption energy, ESP charge difference and Mulliken population ratio was AgY>CrY>CuY>ZnY, which was in perfect agreement with the experimental results. In addition, the ESP analysis showed that the electron transfer path was as follows: H in the quinoline→C inside the quinoline→N in the quinoline→transition metal ion M of the zeolite cluster→O bonded with M→the entire cluster framework, while some electrons from the lower end of the quinoline molecule close to the cluster of the H→O in the outer part of the six-membered ring framework of zeolite clusters; Mulliken population analysis revealed that the adsorption and denitrification mechanism of modified zeolite was primarily the combined effect of σ-donation and d-π* backdonation bonds, with the σ-donation bond being the predominant one.