Reactions of Propane and of n-Butane with Hydrogen over Palladium Catalyst

On 5% Pd/SiO2 and 5% Pd/Al2O3 catalysts, hydrogenolysis of propane affords ethane in high selectivity (S2 ≈ 0.97-0.98); on the latter, the order in H2 is -3.0 and the value of S2 decreases as the H2 pressure falls. The reaction of n-butane with H2 gives chiefly methane and propane in almost equal amounts, except at the highest temperatures (> 650 K) and the lowest H2 pressure (< 0.35 atm): the probability of central bond fission falls as the catalyst becomes deactivated by 'carbon' deposition to a value of ca. 0.05. Skeletal isomerisation to isobutane also occurs with low selectivity (Si ≈ 0.07-0.15). Product selectivities from n-butane are remarkably unaffected by alteration of temperature and of H2 pressure, owing to the predominance of a single reaction pathway; the activation energy is high (250-320 kJ mol-1) and the order in H2 strongly negative (-3.0).