Direct experimental detection of hydrogen radicals in non-oxidative methane catalytic reaction

Non-oxidative conversion of methane to olefins, aromatics and hydrogen (MTOAH) has been reported recently over metal single sites such as iron and platinum. The reaction was proposed to involve catalytic activation of methane followed by gas phase C−C coupling of methyl radicals. This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species (denoted as Fe-reactor). Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C₂ (ethane, ethylene and acetylene) and 31.8% toward BTX (benzene, toluene and xylene), respectively. The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene, which provides an additional route of methane activation apart from catalytic activation.