Platinum-silica hydrogenation, olefins

Infrared spectra of acetylene adsorbed on silica-supported nickel, palladium and platinum [149] in the absence of hydrogen show bands ascrib-able to an olefinic species (J)... 

P. S. Nix and S. Lucki, at our laboratories, have demonstrated (unpublished) the ability of separate platinum and acidic catalysts, as a mixed composite, to perform the skeletal transition from ethyl-benzene to xylenes under hydrogenative conditions (pn, = 11.8 atm., Peb = 1.2 atm. 427 C, r = 3.3 sec.) with 40% conversion to xylenes. Yet at the same temperature, but at atmospheric pressure where production of cyclo-olefin intermediates is not favored, they obtained no measurable conversion even with platinum directly impregnated on the silica-alumina. 

Measurements of competitive hydrogenation of butadiene into butenes on palladium and platinum catalysts supported on silica [30] allowed the determination of the relative adsorption coefficients of dienes and olefins. 

All the catalysts have been tested in the selective hydrogenation of citral. This molecule suits very well to the study of the influence of the nature and the structure of the active phase on its catalytic properties, because it includes three kinds of unsaturations (1) an aldehydic function, (2) a conjugated olefinic bond and (3) an isolated olefinic bond. Moreover, rhodium or platinum supported on silica are not selective for the hydrogenation of citral to diolefinic alcohols (geraniol and nerol) (13, 14). The overall reaction path for reduction of citral trans is represented in figure 5. Depending on the selectivity of the first hydrogenation step, three... 

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