Reduction of hydrocarbon emissions from engine exhaust using zeolitic adsorbers

This paper reports the results of a study on adsorption properties of MFI- FAU-, BEA- and FER-type zeolites towards hydrocarbons present at engine exhaust during the cold start phase. Adsorption measurement under equilibrium and dynamic condition were carried out with several hydrocarbons (ethylene, isobutene, toluene, C4-C5 paraffins), considered as representative of the most common compounds present at engine exhaust. FAU-type zeolite, as well as MFI-type zeolite, showed high affinity for toluene and isobutene, low for paraffins and negligible for ethylene. On the contrary, high affinities for ethylene were found with FER-type, a small pore zeolite. Adsorption tests in real condition were performed at the engine exhaust on both grains (commercial or specifically synthesised) and zeolites crystals deposited on cordierite honeycomb support by an innovative technique. The best global performance, i.e., a hydrocarbon abatement efficiency of 50%, reached after 7 min with a saturation uptake capacity about 1.6%, was obtained using a FAU-type zeolite. On the basis of collected data, the possibility to couple large pore zeolites, such as FAU-type, with small pore size zeolites (likely FER-type, having a good selectivity for ethylene), to realize an efficient hydrocarbon adsorbent trap for reducing cold start emission was, at last, envisaged.