Characterisation of a Commercial Automotive NH3-SCR Copper–Zeolite Catalyst
A commercial copper exchanged zeolite was characterised and studied regarding the selective catalytic reduction of nitrogen oxides (NOX) by ammonia using physicochemical analyses (XRF, XRD, NMR, BET, UV–Visible, IR) and synthetic gas bench test rig, respectively. As expected, two adsorption sites were identified for ammonia: Bronsted and Lewis acid sites, the latter retaining stronger ammonia. Furthermore, ammonia and water adsorb on the same sites, and competition phenomena decrease ammonia storage capacity. Concerning the NOX conversion, in spite of a high efficiency, an important selectivity into N2O is noticed, due to the formation of an ammonium nitrate by-product on the catalyst surface. The limited NOX conversion efficiency at low temperature is due to the weak NO oxidation activity, whereas NH3 oxidation activity at high temperature involves a decrease in NOX reduction.