Alkaline-modified ZSM-5 zeolite to control hydrocarbon cold-start emission

The implementation of Super-Ultra Low Emission Vehicle (SULEV) standards requires fine exhaust gas purification. Adsorbents capable of strong adsorption of hydrocarbons and holding them up to 250300 degrees C were prepared by modification of ZSM-5 (SiO2/Al2O3 = 35) zeolite with Li, K, or Na cations. It was shown that the introduction of Li, Na, and K resulted in enhanced toluene adsorption at high temperatures. The best result was obtained for 2.3%Na-ZSM-5. It was established that an increase in the Li content in ZSM-5 to 5 wt% results in a shift of the high-temperature peak to the high-temperature range. Toluene desorption curves for 5%Li-ZSM-5 and 2.3%Na-ZSM-5 zeolites are identical. Analysis of toluene adsorption isotherms at 20 degrees C for 2.3%Na-ZSM-5 and 5%Li-ZSM-5 revealed that toluene diffusion inside the channels of modified zeolites is extremely slow, and the overall sorption capacity of zeolites with univalent cations decreases as compared with initial ZSM-5. The 5%LiZSM-5 and 2.3%Na-ZSM-5 zeolites characterized by toluene desorption temperatures about 200-400 degrees C are very promising to control the cold-start hydrocarbon emissions. (C) 2017 Elsevier Inc. All rights reserved.