Sulfur and temperature effects on the spatial distribution of reactions inside a lean NOx trap and resulting changes in global performance

摘要: Abstract We experimentally studied the influence of temperature and sulfur loading on axial distribution reactions inside a commercial lean NOx trap (LNT) catalyst to better understand global performance trends. Our measurements were made monolith core, bench-flow reactor under cycling conditions (60-s lean/5-s rich) at 200, 325, 400 °C with intra-catalyst reactor-outlet gas speciation. Postmortem elemental diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses also supplemented our species measurements. For unsulfated catalyst, storage/reduction (NSR) localized in front (upstream) portion monolith, whereas oxygen distributed more evenly along entire length. As result, two axially distinct reaction zones developed working catalyst: an upstream “NSR zone” where both took place downstream storage capacity (OSC)-only zone NSR did not penetrate. The involved less than half LNT 325 400 °C, but it included almost length 200 °C. Sulfation poisoned OSC beginning edge, degradation occurring rapidly distinctly OSC. sulfation proceeded, third (the sulfated zone) moved downstream, concomitant decrease OSC-only conversion. impact conversion was greatest 200 °C, when largest. Ammonia selectivity increased sulfation, which we attributed shortened resultantly reduced consumption NH3, slipping from zone, by Lower temperatures NH3 selectivity. Nitrous oxide decreasing showed little dependence sulfation. proposed explanations for these trends N2O based shifts competing rates three zones.