Stabilization of Cu+ ions in BEA zeolite: Study by FTIR spectroscopy of adsorbed CO and TPR

A Cu-BEA sample prepared by conventional ion-exchange was studied by TPR and IR spectroscopy of CO used as a molecular probe. The TPR pattern consists of several peaks at 484, 530, 608, 695, 783 and 988 K. On the basis of the FTIR spectra of CO adsorbed at 100 K the former four TPR peaks were assigned to reduction of Cu2+ to Cu+, and the last two, to the reduction of Cu+ to Cu0. On the non-reduced sample, Cu2+–CO species and a small amount of Cu+(CO)n carbonyls are observed by IR spectroscopy after CO adsorption. Reduction of the sample by CO at temperatures up to 723 K progressively creates Cu+ sites forming different kinds of mono- and polycarbonyl species. The state of copper in the sample is similar after reduction at 723 K with either CO or H2: copper is mainly monovalent, although some Cu0 is also detected with the hydrogen-reduced sample. The results evidence that Cu+ ions are stabilized in BEA zeolite, similarly to other monovalent cations, such as Co+ and Ni+.