Hydrogenolysis of Some Paraffinic Hydrocarbons on Supported Catalysts of Ruthenium, Nickel, Cobalt, and Iron

Abstract

<p>The hydrogenolysis of propane, n-hexane, 2,3-dime-thylbutane, and 2,2-dimethylbutane was studied over supported catalysts of ruthenium, nickel, cobalt, and iron, some containing structural promoters. The catalysts were prepared by impregnation of several supports, and were characterized using mainly atomic absorption and chemisorption techniques. A differential reactor system was used, consisting of a fixed-bed reactor and an external recycle pump. The data from propane hydrogenolysis were fitted to a power rate equation and a selectivity equation. The results are in general agreement with those of similar experiments with ethane. The products from the hydrogenolysis of the hexanes were fitted to selectivity equations that were based on reaction networks derived for reversible adsorption-desorption of the hydrocarbons and irreversible rupture of the carbon-carbon bonds of the surface species. The product distributions were measured over a wide range of conversion (10 to 80%), but in most cases only at one temperature. In the sequence -ruthenium, nickel, cobalt, iron - the distribution shifts toward smaller hydrocarbons. Ruthenium tends to split the carbon-carbon bonds in a straight chain with equal probability, while nickel preferably splits terminal bonds. Structural promoters increase the activity of the nickel and cobalt catalysts, and stabilize the iron catalysts. Because of this the catalysts on low area supports had activities very similar to those on high area supports; the amount of metal, however, was higher on the low area supports.</p>