The effects of protons on the hydrogenolysis of neopentane over rhodium catalysts: Rh/Hy, Rh/NaHY, and Rh/SiO[sub 2]

The hydrogenolysis of neopentane (2.2-dimethylpropane) has been studied over the rhodium catalysts Rh/Hy, Rh/NaHY, and Rh/SiO[sub 2]. The catalytic activity follows the sequence: Rh/HY>Rh/NaHY [approx] Rh/SiO[sub 2]. For all catalysts, the conversion of neopentane was 100% selective to hydrogenolysis products, methane, and isobutane; they are formed in a ratio of 1:1. In an attempt to determine the true activation energies from the apparent activation energies derived from the Arrhenius curves, corrections were made for the preequilibrium between gaseous and physisorbed neopentane. The adsorption of neopentane on the metal-free supports was determined; isosteric heats of adsorption were calculated from these data. For zeolites NaY and HY they are 8.2 and 7.0 kcal/mol, respectively. After correcting for the preequilibrium, the true activation energies are 33.5 and 38.8 kcal/mol for Rh/HY and Rh/NaHY, respectively. The results lend support to the concept that the superior activity of Rh/HY is due to the [open quotes]electron deficiency[close quotes] of the rhodium particles. 52 refs., 4 figs., 4 tab.