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Nuclear magnetic resonance studies of ruthenium and rhodium exchanged Y-zeolites
Abstract
The $\sp{129}$Xe nuclear magnetic resonance (NMR) of xenon gas sorbed in zeolites has been combined with other experimental methods to characterize the state of ruthenium contained in Y-type zeolites at various stages of catalyst treatment. The adsorption of carbon monoxide on ruthenium and rhodium in Y zeolites has been investigated using high resolution magic-angle spinning NMR methods. The xenon NMR experiments, combined with volumetric oxidation/reduction experiments and transmission electron microscopy, reveal that most of the ruthenium is highly dispersed and occupies the faujasite supercages upon initial ion exchange. Initial exposure to hydrogen gas at room temperature causes nearly complete reduction of Ru$\sp{3+}$ to Ru$\sp{0}$. Exposure of the reduced catalyst to oxygen at elevated temperatures results in quantitative oxidation to RuO$\sb2$, and no detectable migration of the ruthenium species accompanies this oxidation. Reduced ruthenium, however, is found to migrate to the exteriors of the zeolite crystallites upon high temperature treatment, as confirmed by transmission electron microscopy. Three types of adsorbed carbon monoxide, linear, bridging, and dicarbonyl species, are identified in ruthenium and rhodium exchanged zeolites by $\sp{13}$C magic-angle spinning NMR. In ruthenium-Y zeolites the bridging species is found to be thermally activated; whereas, this species forms at ambient temperatures in rhodium exchanged Y zeolites. This bridging species is inhibited in Rh-Y zeolites when the sodium co-cation is replaced by calcium or hydrogen. Carbon dioxide is formed via the water-gas shift reaction at room temperature in reduced ruthenium zeolites, but not in rhodium exchanged zeolites. Both catalysts exhibit CO$\sb2$ formation when CO is exposed to an unreduced sample.
Subject Area
Chemistry|Analytical chemistry
Recommended Citation
Shoemaker, Richard K, "Nuclear magnetic resonance studies of ruthenium and rhodium exchanged Y-zeolites" (1988). ETD collection for University of Nebraska-Lincoln. AAI8818657.
https://digitalcommons.unl.edu/dissertations/AAI8818657