Spectroscopic characterisation of Cu–Al2O3catalysts 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.