Characterization of the Host Monometallic Catalysts

The dispersions (number of surface metal atoms/total metal atoms) of the samples are determined by chemisorptions of hydrogen, oxygen and CO at 25 °C [98]. Prior 

In some cases, the metaUic particle size is determined by electron microscopy (JEOL100 CX) and the dispersion is correlated to the average metalUc particle size, assuming that the metallic particles have a cubo-octahedral shape [66]. 

With plahnum and palladium catalysts, supported on siUca, alumina and active carbon, both H2, O2 and CO probe molecules are available for dispersion measurements. For rhodium, the various values are taken from the work of Ferretti et al. [102]. For ruthenium and iridium, O2 cannot be used as a probe molecule for dispersion measurements, because there is formahon of bulk oxides. With nickel, only H2 gives reUable results, O2 and CO cannot be used as probe molecules for dispersion measurements, because there is formation of bulk oxides with O2 and metal-carbonyls with CO, but the dispersion of the sample can be additionally measured by magnetic measurements. 

Before any adsorption measurement, the catalysts are reduced under flowing hydrogen at 380 or 450°C. It was demonstrated that Rh, Pt and Pd were fully reduced above 380 °C. Ru, Ir and Ni were treated under flowing hydrogen at 450 °C for 5 h. In these conditions, Ru and Ir are fuUy reduced and the reduction extent 

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