Abstract
Adsorption of hydrogen and deuterium on samples of chromia and on nonstoichiometric zinc, cobalt, and manganese chromites (M/Cr atomic ratio 1:1; M = Zn, Co, Mn), previously activated in hydrogen and vacuum, was studied by means of Fourier transform-infrared spectroscopy. Parallel CO adsorption experiments indicate that all four catalysts are essentially in an oxide form after hydrogen adsorption. Only in the case of the cobalt compound are zerovalent centers observed. Terminal hydrides CrH are formed on chromia, whereas on the three chromites, both terminal and bridged hydride species, thought to be bonded to Zn 2+, Co 2+, and Mn 2+ centers, respectively, are observed. These assignments are based on the H(D) isotopic shift and on a comparison with the spectra of known hydride species of the same metals. The mechanism of formation of these adsorbed forms is briefly discussed.
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