Fundamental studies of hydrocarbon conversions over supported bimetallic catalysts
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The reactions of ethane and ethylene over selected silica-supported group VIII metal catalysts have been investigated using reaction studies and nuclear magnetic resonance (NMR) spectroscopy. The activity of the ruthenium-group IB bimetallic system for the ethane hydrogenolysis reaction was investigated as a function of group IB metal content and ethane and hydrogen partial pressures, while the reactions of ethylene over silica-supported platinum catalysts were studied using NMR;The turnover frequency of the silica-supported ruthenium catalysts for ethane hydrogenolysis as either copper or silver was added tended to change as the group IB metal was first added until a critical point was reached. After this point, increasing the proportion of group IB metal had no significant effect on the specific activity of the catalyst. As was expected, copper, the more strongly segregating element, reached this critical point before silver. The critical point is believed to correspond to the point at which all the edge and corner sites in the supported bimetallic crystallite are occupied by the group IB metal;The apparent orders of reaction for ethane hydrogenolysis over the ruthenium-group IB catalysts was measured as a function of temperature. It appears from these measurements that the principal role of the edge and corner sites of a ruthenium catalyst for this reaction is the desorption and adsorption of hydrogen. At the higher temperatures studied, it appears that copper occupying the low coordination sites of a bimetallic crystallites is also active for the desorption/adsorption of hydrogen;The reactions of ethylene over silica-supported platinum catalysts has been investigated using NMR. The ethylene to surface platinum atom ratio used in this work was in the 10 to 20 range, far higher than that used for typical single crystal studies. No significant activity was observed at room temperature. At temperatures in the 400 K to 550 K region a number of products were identified, including ethane, methane, and cis- and trans-but-2-ene. At still higher temperatures coke was formed on the surface of the catalyst. This coke was characterized as being predominantly aromatic in nature.