Hydrogenolysis of propane, n-butane and isobutane on rhenium/alumina catalysts

Abstract

The hydrogenolysis of n-butane and isobutane and of propane has been studied on Re/Al₂O₃ catalysts containing 1.5, 2.2 and 2.75% Re; they were reduced at 763 K. The reactor temperature was raised stepwise from its initial value (330–360 K in later experiments) to 600 K, analyses being performed at 10 or 15 K intervals, the process being repeated as the temperature was returned to its starting value. This thermal cycle was repeated at least once in every case.

With n-butane, the rate initially obeyed the Arrhenius law (the α-phase), but deactivation set in at about 400 K and the rate passed through a maximum. It subsequently renewed its upward trend (the β-phase), but it appeared that the surface was cleansed at high temperature, as the rate was much faster for most of the cooling stage (γ-phase). In the case of n-butane, the rates at each point of the cycle were quite reproducible in the second and subsequent cycles; the rates for isobutane and for propane showed little change with cycle number, although with propane deactivation started at low temperature. Rates, activation energies and product selectivities were closely reproduced, especially in the γ-phase. This sustained hysteresis of catalytic rate is explained by an alternate coking and cleansing of the surface of the Re particles.