B. Torok et al., HYDROGEN PRESSURE-DEPENDENCE IN THE RING-OPENING REACTIONS OF PROPYLCYCLOBUTANE OVER PD SIO2 CATALYST/, Catalysis letters, 31(4), 1995, pp. 421-429
Temperature dependence and the effects of hydrogen pressure on the rat
e and regioselectivity were studied in the ring opening of propylcyclo
butane over a low-dispersion Pd/SiO2 catalyst. At a certain compositio
n (1.33 kPa of propylcyclobutane and 20 kPa of H-2) the reaction rate
versus temperature curve was found to pass through a maximum. At each
temperature the ring opened selectively (or exclusively at 423 K) in t
he sterically more hindered direction over the clean surface as well a
s over the steady-state catalyst, yielding n-heptane as the major prod
uct. The hydrogen pressure versus turnover frequency curves were of sa
turation type for both products over the initial surface at 523 K. Ove
r the steady-state surface, however, the reaction mechanism changed: r
ing-opening rate versus hydrogen pressure curve passed through a maxim
um for n-heptane, while it remained of saturation type for 3-methylhex
ane. For rationalizing the high regioselectivity toward n-heptane form
ation, the anchoring effect of the propyl side-chain was suggested.