Homogeneous Gas-phase Pyrolyses using a Wall-less Reactor. IV. Comparative Surface-Nonsurface Effects with Cyclopropane

The rates of pyrolysis of cyclopropane in nitrogen have been determined using a wall-less reactor at temperatures of 600–740 °C and a total pressure of 1 atm. In the presence of oxidized stainless steel. quartz, or carbon coated steel rods the rate of conversion to propylene is 1.9 times the rate under homogeneous conditions. A maximum in surface effect was observed at S/V = 0.6 cm −1 . A small but increased amount of methane and ethene are formed under surface conditions as compared to homogeneous conditions. Several possible mechanisms for the rate enhancement by surface are discussed. The most likely possibility is surface interaction with the cyclopropane molecule to form the diradical followed by its surface promoted conversion to propene. The importance of determining surface effects by comparing surface rates with totally homogeneous rates is emphasized.