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

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).