Hydrocarbon conversions with some intermetallic catalysts

The intermetallic pseudo-binary alloys of the general type ZrRh_3-xPd_x and ZrRh_3-xRu_x (0 < × < 3) have been prepared by argon arc melting and melt quenching of the constituent elements. The alloys were powdered and employed as catalysts for (i) hydrogenation of oct-1-yne in the liquid phase at 101.32 kPa total pressure and 70°C, (ii) hydrogenation of buta-1,3-diene in the gas phase at 101.32 kPa total pressure in the temperature range 45–225°C, and (iii) hydrogenolysis of n-pentane in the gas phase at 101.32 kPa total pressure and in the temperature range 200–400°C. Activity and selectivity measurements were made with respect to (i) alkene formation for the hydrogenation reactions, and (ii) C₂ + C₃-alkane formation for the hydrogenolysis reaction. The activity of the alloy series appears to correlate to some degree with the electronic properties and hydrogen sorption capacity of the intermetallic alloys. Auger electron spectroscopy measurements revealed that for ZrRh_3-xPd_x alloys both the surface and bulk compositions were in good agreement; this behaviour is contrasted briefly with that of CeRh_3-xPd_x alloys which, unlike ZrRh_3-x alloys, suffered significant oxygen interaction in the surface and sub-surface layers, although this did not affect Rh:Pd ratios. Catalysts that were active for hydrogenation were inactive for hydrogenolysis and vice versa. However, selectivity values for the hydrogenation reactions generally reflected the behaviour of the predominant noble transition metal. Again, the behaviour of ZrRh_3-xPd_x and CeRh_3-x alloys is contrasted, since the latter were more selective for butene formation from buta-1,3-diene, and attributed to the oxygen Contamination of the surface. Further more, the selectivity of both ZrPd and CePd, for 1-octyne and butu-l j-dene hydrogenation was significantly greater than that of palladium by virtue of the fact that the intermetallics were found to be largely inactive for alkene hydrogenation.