13C high resolution NMR studies of adsorption and reaction of ethylene on silica-supported Ru and Ru-Cu catalysts

The adsorption and subsequent reaction of ethylene on silica-supported Ru and Ru-Cu bimetallic catalysts have been studied via nuclear magnetic resonance (NMR) employing a variety of experimental nuclear spin dynamics. NMR of 13C using cross polarization (CP) and magic angle spinning (MAS) allowed us to simultaneously observed transformations of chemisorbed species and weakly adsorbed molecules. Direct 13C excitation allowed quantitative measurements of various species on the surface. At room temperature the ethylene adsorbed on the ruthenium catalysts rapidly and converted to strongly adsorbed acetylide and alkyl species. Weakly adsorbed ethane, butane and cis- and trans-2-butene were observed. The butene slowly hydrogenated to form additional butane. When the temperature was raised to 140 degC propane and methane were observed suggesting hydrogenolysis of the product molecules. The introduction of copper into the catalysts reduced the hydrogenation capability while still maintaining the ability to form dimeric products. In addition to butene and butane, butadiene was observed on the bimetallic catalysts. (author). 55 refs.; 8 figs.; 1 tab