Effect of metal-metal and metal-support interaction on activity and stability of Pd-Rh/alumina in CO oxidation

A series of Pd-Rh/alumina catalysts with total precious metals loading of 0.2 wt.% was prepared by means of mechanical mixing of monometallic precursors and incipient wetness impregnation of the support with dual complex salt. Gamma and delta alumina supports were obtained from commercial aluminum hydroxide by calcinations at 720 and 1000 °C respectively. Supports were examined by electron paramagnetic resonance spectroscopy, low-temperature nitrogen adsorption, X-ray diffraction analysis and photoluminescence spectroscopy. It was shown that concentration of donor sites of the supports differs according to distinctions between values of their specific surface areas. Finally, the strength of metal-support interaction is getting much weaker in the case of δ-Al₂O₃. Bimetallic Pd-Rh species with strong metal-metal interaction supported on γ-Al₂O₃ were found to be characterized by superior high-temperature stability. Pd/Rh ratios of 3:2 and 7:3 were shown to be the most appropriate for this purpose.