Spectroscopic characterisation of Cu–Al2O3 catalysts for selective catalytic reduction of NO with propene

Abstract

Copper–aluminium mixed oxide catalysts (Cu–Al2O3) for selective reduction of NO with propene (C3H6-SCR) were characterised as a function of Cu content. The results from different techniques, Cu K-edge and Cu L3-edge XANES, diffuse reflectance UV–Vis, XPS, and XRD were combined to develop coherent description of the phases present and cation site distribution in Cu–Al2O3. Both the bulk and the surface of Cu–Al2O3 consist of Cu2+ cations at tetrahedral or octahedral sites of the Al2O3 matrix, forming an aluminate phase in a wide range of Cu content (1–30 wt.%). Cu L3-edge XANES analysis succeeded in quantifying the fraction of tetrahedral and octahedral Cu2+ ions; the fraction of octahedral Cu2+ decreased as Cu concentration increased. The catalytic activity for C3H6-SCR per surface area of the catalysts increased as surface Cu2+ concentration increased, indicating that Cu2+ ions in the aluminate phase are responsible for the activity. The activity per surface Cu2+ decreased as surface Cu2+ concentration increased, which coincides with the decrease in the fraction of octahedra. The Cu2+ cations in octahedral sites should be responsible for the higher intrinsic activity.