Selective catalytic reduction of NOx from exhaust of lean-burn engine over Ag-Al2O3/cordierite catalyst

Abstract

A highly effective Ag-Al₂O₃ catalyst was prepared using the in-situ sol-gel method, and characterized by surface area using nitrogen adsorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The catalyst performance was tested on a real lean-burn gasoline engine. Only unburned hydrocarbons and carbon monoxide in the exhaust were directly used as reductant (without any external reductant), the maximum NO_x conversion could only reach 40% at 450?C. When an external reductant, ethanol was added, the average NO_x conversion was greater than 60%. At exhaust gas temperature range of 350 500?C, the maximum NO_x conversion reached about 90%. CO and HC could be efficiently oxidized with Pt-A₂O₃ oxidation catalyst placed at the end of SCR converter. However, NO_x conversion drastically decreased because of the oxidation of some intermediates to NO_x again. The possible reaction mechanism was proposed as two typical processes, nitration, and reduction in HC-SCR over Ag-Al₂O₃.