Critical behavior of hydrogen bonds observed in high-pressure nuclear quadrupole resonance studies

Abstract

A summary of our NMR results is presented in Table I . Integration of the line shapes of the sample exposed at room temperature yields a total spin density of 1.3 X lozo CO’s per gram of catalyst. Using a CO/Ru ratio of 1 for linear CO and a CO/Ru ratio of 2 for the dicarbonyl, we obtain a dispersion of 30%. Chemisorption measurements yielded a dispersion of 27%. Upon high-temperature exposure, a greater number of dicarbonyls are formed, indicating that dicarbonyl adsorption is activated. A bridged species is also formed, whereas the relative proportion of linear species decreases. We cannot determine whether the bridged species derives directly from the linear species, or whether the adsorption of the bridged species precludes the presence of a linear species a t a particular site. Since no change is evident in the metal surface area after heating, this change in CO distribution cannot be attributed to a change in metal particle size. We have shown that I3C magic angle spinning NMR can be used to identify and quantify CO adsorbates. This technique holds promise for studying differential reactivity of adsorbed species. In addition, since dicarbonyl species may only bond to isolated atoms, the degree of atomic dispersion may be detected by 13C NMR.