Water Droplet Microlightning Enables Catalyst-Free Alkane Dehydrogenation under Ambient Conditions

We report that microlightning generated between oppositely charged microdroplets during the spraying of pure water surrounded by alkane vapor can initiate catalyst-free alkane dehydrogenation under ambient conditions. When cyclohexane (C6H12) vapor is introduced into the water spray, a series of dehydrogenated products including cyclohexenyl (C6H9+), cyclohexadienyl (C6H7+), and phenyl (C6H5+) cations are detected by high-resolution mass spectrometry. Control experiments establish that both water and molecular oxygen are essential for this transformation to occur. The capture of alkyl radical intermediates by mass spectrometry suggests that the dehydrogenation proceeds through microlightning-induced radical pathways. Furthermore, the reaction can be scaled up, achieving alkene formation rates of up to 12 mM h–1 as quantified by gas chromatography. Beyond cyclohexane, similar dehydrogenation is also observed for other aliphatic substrates. These findings demonstrate a catalyst-free and sustainable method for alkane dehydrogenation under ambient conditions.