COMPUTER ASSISTED DESIGN OF POROUS SOLIDS FOR VOC'S EMISSION CONTROL BY ADSORPTION IN VEHICLE COLD START

摘要

Catalysts for vehicle emission control usually start working at around 473 K. The catalyst requires a period of 60 to 120 s to reach this temperature; during that time up to 80% of hydrocarbons in a drive cycle are emitted~1. The emissions control during this "cold start" period is essential to reduce the environmental impact of gasoline engines. Among all the solutions studied up to now, the use of HC adsorbents, "hydrocarbon traps", before the three-way catalyst seems to be the most relevant from a scientific-technological point of view. The critical factors for any emission trap are: i) high adsorption capacity of hydrocarbons at low temperatures, ii) desorption starting at temperatures higher than 473 K, iii) a reversible adsorption process and iv) solid material resistant at temperatures higher than 1000 K. The maximum values of these factors are limited by properties of the solids like pore volume, pore structure, chemical nature of the solid, extra-framework atoms, etc. Zeolites have been found to be the preferred adsorbents for these applications, mainly due to their stability under severe process conditions.