Alloying Effect in Low Loaded Rh Catalysts Supported on High Surface Area Alumina on Their Activity in CH4 and NO Decomposition

Abstract

In the alloys of transition metals (TM) and main group ones (MGM) the valence electrons from MGM can fill the d band of the TMs entirely and slightly increase the number of electrons in their s band (Azaroff, 1960; Kittel, 2005). Such Rh atoms enriched in electrons, present in Al-Rh alloys, were found to be very active electron donors (Pietraszek et al., 2007). It was revealed that they transfer the electrons to the antibonding Л orbital of adsorbed nitric oxide molecules causing NO decomposition to dinitrogen and dioxygen (Pietraszek et al., 2007). Due to the great difference in the Al and Rh electro-negativity, the alloys are sometimes considered as nonstoichiometric chemical compounds. Because of the large range of nonstoichiometry those compounds should rather be estimated as intermediate phases (IP) (Azaroff, 1960). The presence of the Al-Rh alloy nanocrystallites isostructural with Al9Rh2 (Bostrom et al., 2005) was earlier revealed in the freshly prepared Rh/δAl2O3 catalysts containing 0.06 and 1.5 wt.% Rh (Pietraszek et al., 2007; Zimowska et al., 2006)...