A volumctric and microcalorimetric study of the adsorption of hydrogen, at 296K, on a scries of silica-supported nickel and nickel-copper catalysts was carried out. Alloying with copper decreases both the afiiiity of nickcl for hydrogen and the heat of adsorption of hydrogen. The hydrogen covcrage, under standard conditions, on a given alloy is correlated to the saturation magnetization of the metal atoms in the alloy. The decrease of the differential heats of adsorption of hydrogen, resulting either from alloying or from thc heterogeneity induced by pre-adsorbed hydrogen, can be correlated with the changes of electron dcnsity of states, at the Fermi level, for the surface nickel atoms.
A calorimetric study of the adsorption of carbon monoxide, at 296 K, on a series of silica-supported nickel and nickel-copper catalysts was carried out. The experimental results were compared with previously published i.r. spectroscopic and magnetic data for the same systems. In agreement with the Chatt-Dewar model for CO chemisorption on metals, changes of the heat of formation of metal-CO bonds can always be associated with shifts of the frequency of the C-0 stretching vibration. The heat of the metalLC0 bond formation appears to be related to the position of the Fermi level at the metal surface. Formation of both linear and bridged adspecies, in definite proportions on each alloy, would obey a concerted mechanism, controlled by the electronic properties of the surface nickel atoms.
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