Hydroisomerization of cis-Stilbene into trans-Stilbene on Supported Heterogeneous Metal Catalysts (Rh, Pd, Pt, Ru, Ir/α-Al2O3)

The hydroisomerization of a cis -isomer to produce a trans -isomer on Rh, Pd, Pt, Ru, and Ir/α-Al 2 O 3 catalysts is studied. It is shown that Rh and Ru catalysts on which the hydroisomerization reaction mostly takes place exhibit the most favorable characteristics, whereas on the other metals, the main route is the hydrogenation reaction. Rh/α-Al 2 O 3 is the optimum catalyst, since it has much higher activity than Ru/α-Al 2 O 3 . It is found that the increased selectivity of the trans -isomer formation is facilitated by a decrease in the hydrogen pressure and by an increase in the substrate concentration. The maximum selectivity is achieved when the reaction is carried out in nonpolar n -hexane and toluene, whereas in the case of the more polar tetrahydrofuran (THF), dimethylformamide (DMFA), and methanol both the reaction rate and the selectivity of the trans -isomer formation decline.