Bifunctional Cu/H-ZSM-5 zeolite with hierarchical porosity for hydrocarbon abatement under cold-start conditions

A key target to reduce current hydrocarbon emissions from vehicular exhaust is to improve their abatement under cold-start conditions. Here, we demonstrate the exceptional properties of a hierarchical Cu/H-ZSM-5 zeolite-based system as a catalytic trap. The largely increased external surface area coupled with the preserved intrinsic properties attainable upon alkaline treatment and subsequent acid washing of a conventional ZSM-5 zeolite enable an improved dispersion of copper species in the hierarchical counterpart. The impact of post-synthetic modification on the preparation of copper-containing ZSM-5 is clearly revealed by XRD, N-2 sorption, FTIR, NH3-TPD, TEM, SEM, and HAADF-STEM. By providing stronger adsorption sites, the introduction of copper species improves the retention of propene and toluene with respect to the protonic zeolites, and enables their further conversion to carbon dioxide and water rather than their emission in the exhaust. The equivalent adsorption capacity and improved oxidation activity and lower susceptibility to deactivation exhibited by the hierarchical Cu/H-ZSM-5 catalyst vis-a-vis its conventional counterpart yield a superior bifunctional catalyst able of reach full hydrocarbon conversion under realistic operating conditions. (C) 2014 Elsevier B.V. All rights reserved.