In-situ formation of [AlO4]0 site for confined catalytic cracking to ethylene with low methane selectivity

Ethylene, one of the major basic chemicals in the modern chemical industry, has been industrially produced mainly through intensive energy-consuming steam cracking processes from light oil fractions or shale gas operated above 800 °C following the radical mechanism and seriously suffering from high methane selectivity. Herein, we report an efficient catalytic cracking reaction of 1-pentene over a tailored ZSM-5 catalyst at 700 °C with a C2H4/C3H6 ratio of 1.31 and a CH4 selectivity below 5%, which provides an energy-saving and economically viable route for ethylene production from light oil fractions, seamlessly integrating with the existing industrial catalytic cracking processes. Mechanistic studies unveil an interesting type of zeolite catalysis different from the typical acid catalysis following the carbenium ion mechanism, termed as the confined catalytic radical (CCR) mechanism in which 1-pentene dehydrogenates to gaseous pentenyl radicals (C5H9•) at non-acidic [AlO4]0 sites of ZSM-5 in situ formed by dehydrogenation of bridging hydroxyls, whose subsequent reactions confined in ZSM-5 produce more C2H4 than C3H6. These findings significantly broaden the concept and application of zeolite catalysis. Ethylene is vital, but steam cracking (>800 °C) is energy-hungry and CH₄-prone. This work cracks 1-pentene over tailored ZSM-5 at 700 °C via a confined catalytic radical mechanism, giving C₂H₄/C₃H₆ = 1.31 with <5% CH₄, compatible with existing FCC processes.