Experimental and simulation investigation on the hydrocarbon adsorption performance of the transition metal ion-modified zeolite during cold start process of automotive engine

To optimize the hydrocarbon adsorption capacity of zeolite adsorbents, Fe-beta zeolites with iron loadings of 1 %, 3 %, and 5 wt% were prepared using an isovolumetric impregnation method. The adsorption and desorption strengths of Fe-beta and prototype H-beta zeolites on hydrocarbon mixtures of acetylene (C2H2), acetaldehyde (C2H4O), and 1-butene (C4H8) were determined by adsorption breakthrough tests and temperature programmed desorption experiments. The experimental results showed that the amount of hydrocarbon gases adsorbed by beta zeolite was 1-butene > acetaldehyde > acetylene. The introduction of iron ions enhanced the adsorption performance of beta zeolite for C4H8 and C2H4O but reduced the adsorption amount of C2H2; when the iron loading increased, the adsorption amount of C2H4O increased, while the adsorption capacity of C4H8 decreased; iron modification improved both the retention amount and retention temperature of C4H8. Further molecular simulations were used to investigate the hydrocarbon adsorption and diffusion mechanisms of transition metal (Fe2+, Cu2+, Zn2+) modified zeolites (MFI, MWW, BEA). The adsorption simulation results showed that transition metal modification led to enhanced hydrophilicity as well as local electric field of the zeolites, and increased adsorption of C2H4O while decreased adsorption of C4H8. Three transition metal ions showed less difference in the effects of zeolite modification. When hydrocarbon molecules diffused inside the zeolite, the higher temperatures led to faster diffusion, hydrocarbon molecules with larger diameters and stronger polarities were more difficult to diffuse, and the influence of temperature on the diffusion coefficient of the hydrocarbon molecules was reduced in the case of multi-component diffusion.