Spectroscopic studies of surface copper spinels. Influence of pretreatments on chemical state of copper

Abstract

The nature of copper species of a series of alumina-supported copper samples was investigated by the kinetics of reduction, x-ray photoelectron spectroscopy, temperature-programmed desorptiob-mass spectrometry of chemisorbed NO and infrared spectroscopy of chemisorbed NO and CO probes. The role of these copper species was also examined in the catalytic decomposition of NO. The surface properties of copper were found to depend strongly on both Cu loading and calcination treatment. At Cu contents as low as 0.6 wt.%, Cu2+ ions form a well-dispersed interacting phase at the alumina surface, which upon calcination forms a surface spinel CuAl,O,. At copper contents up to 3.2 wt.%, both the surface spinel CuAl,O, and a segregated CuO phase were clearly distinguished. The partial reduction of these species upon thermal treatment under high vacuum, the ability of the surface sites to chemisorb NO and CO probes and their implications in the catalytic decomposition of NO are discussed.

Adsorption of nitric oxide and temperature programmed desorption on nonstoichiometric nickel–copper manganites

“…The presence of an intense desorption peak of NO at a temperature as low as 558C (Fig. 2) evidences the presence of weakly bound surface species, and similar conclusions have already been drawn in the case of copper±alumina compounds [6]. The occurrence of different desorption peaks can be due to several causes [7±9]: (i) presence of distinct adsorption sites; (ii) formation of various surface species; and/or (iii) existence of interactions between the adsorbed molecules leading to a variation of the activation energy for the desorption of NO as a function of the coverage.…”

Thermal decomposition of a hydrotalcite-containing Cu–Zn–Al precursor: thermal methods combined with an in situ DRIFT study

“…The absence of any crystalline aluminium phase indicates that Al 3+ is incorporated as amorphous alumina. However, the formation of surface Cu-Al and/or Zn-Al spinels 24 cannot be ruled out. The broad XRD peaks indicate that the Cu and Zn oxides are ill-defined crystalline phases.…”

CO2 hydrogenation over Pd-modified methanol synthesis catalysts

“…The weight percentage corresponding to the area under each peak is also tabulated in Table 1. The peak at 935.5±936.0 eV is assigned to Cu 2 in a CuAl 2 O 4 spinel-like environment [11], and the peak at 933.4 eV is attributed to Cu 2 in CuO. The disappearance of the satellite peak and the simultaneous shift of the principal Cu 2p 3/2 peak towards lower BE upon H 2 -reduction at 553 K lead to the conclusion that the copper species are Cu or Cu 0 , but in no case Cu 2 .…”