Probing the existing state of Cu(ii) in a Cu–Al spinel catalyst using N2O decomposition reaction with the aid of conventional characterizations

Abstract

Cu–Al spinel solid solution as a sustained release catalyst has been efficiently applied in methanol steam reforming. The non-spinel CuO species in this catalyst plays a crucial role in initiating the reaction. This paper systematically studies the existing state of the copper species using N₂O decomposition reaction in combination with other characterization techniques. The non-spinel CuO is composed of free CuO and interacting Cu(II) forming Cu–O–Al bonds. The catalytic activity is related to the existing state of Cu(II), which determines the generation of Cu⁺ active centers. It has been verified that highly dispersed free CuO facilitates the in situ generation of the Cu⁺ active centers. Hence, free CuO shows the ability to catalyze the decomposition reaction, while the interacting Cu(II) and spinel type Cu(II) reveal little activity. The activity of CuAl-950 is enhanced dramatically when the interacting Cu(II) is converted to free Cu(II) by reduction–oxidation treatment. Therefore, we suggest that N₂O decomposition may be used as a reliable method to probe the existing state of Cu(II).