Effect analysis on hydrocarbon adsorption performance of transition metal modified zeolites in the gasoline engine during cold start process using Monte Carlo method

Abstract

Zeolite molecular sieves are commonly used for adsorption of hydrocarbons(HCs) during cold start phase of gasoline engines. In this work, the adsorption properties of three zeolites modified with three transition metal ions(Fe2+, Cu2+ and Zn2+) were investigated for the HCs adsorption using the Monte Carlo method. Adsorption simulations were carried out with ethylene and propylene as probe molecules or with a mixture of five hydrocarbon and water molecules. The introduction of transition metal cations enhances the local positive electric field within the molecular sieve, enabling it to engage in stronger adsorption interactions with adsorbate molecules, which significantly improves the adsorption performance of the molecular sieve. For single-component adsorption, Zn2+-MFI with a Si/Al ratio of 7 showed the best adsorption of ethylene, with a high adsorption capacity of 149.19 molecules per cell at 298 K, which was 1.47 times higher than that of pure silicon. The enhanced hydrophilicity of the modified zeolite resulted in a substantial increase in the adsorption of water molecules during multicomponent adsorption. The limited adsorption sites and intermolecular competition for adsorption resulted in the occupation of adsorption sites by large hydrocarbons and a decrease in the adsorption of the remaining small molecules.