Gas-phase free radicals in the catalytic decomposition of hexane over tungsten. A modulated-beam mass spectrometric study

Desorption of alkyl and alkenyl (methyl, ethyl, allyl, and propyl) radicals from hot surfaces in the low-pressure (1 x 10^(12) - 8 x 10^(12) molecules cm^(-3) catalytic decomposition of hexane over W (1100-1800 K) and Pt (850-1400 K) has been studied by modulated-beam mass spectrometry. Time-of-flight analysis (phase spectrometry) of reaction products provided direct evidence about their identity. The effects of temperature, pressure, and surface treatment upon radical yields have also been investigated. Trapping of reactive species with iodine in a tandem reactor confirmed the presence of alkyl radicals. A mechanism is proposed in which free radicals, once formed, either desorb from the surface or decompose further into smaller fragments and olefins.