Effect Analysis on Hydrocarbon Adsorption Enhancement of ZSM-5 Zeolite Modified by Transition Metal Ions in Cold Start of Gasoline Engine

The adsorption effects of transition metal modified ZSM-5 zeolite on the main hydrocarbon emission components of gasoline engine cold start include acetylene (C2H2), ethylene (C2H4), acetaldehyde (C2H4O), propylene (C3H6), 1-butene (C4H8) and benzene (C6H6) carbon monoxide (CO), carbon dioxide (CO2) and water vapor (H2O) were studied by experiments and molecular simulation. Through the hydrocarbon adsorption breakthrough experiment, the promotion effect of Fe-ZSM-5 zeolite on the adsorption of hydrocarbon emissions from cold start was confirmed. Results showed that the Fe modification improved the adsorption rate of zeolite on C4H8 and C2H4O. With the increase of Fe mass fraction, the adsorption capacity of zeolite for C2H4O increased, while the adsorption capacity for C4H8 decreased. The adsorption mechanisms of 9 main exhaust components from cold start on M2+ (M = Fe, Cu and Zn) modified ZSM-5 zeolite were studied by molecular simulation. Under the cold start condition, the adsorption capacity of H2O is the largest, between 1.5 and 4 mmol/gzeo, one order of magnitude higher than that of CO2 (0–0.3 mmol/gzeo), C6H6 (0–0.16 mmol/gzeo), C2H4O (0–0.5 mmol/gzeo) and C4H8 (0–1.6 mmol/gzeo), and 3–4 orders of magnitude higher than that of CO, C2H2, C2H4, C3H6. Results showed that the adsorption priority of molecules on transition metal ion modified ZSM-5 zeolite was determined by functional group charge number, molecular weight and molecular polarity. The zeolite with higher ion exchange ratio has a larger adsorption capacity for oxygen-containing molecules such as H2O, CO2 and C2H4O. Reducing the ion exchange ratio was conducive to the adsorption of hydrocarbons such as C4H8.