Hydrocarbon Degradation by Contact with Anoxic Water Microdroplets

Abstract

Oils are hydrophobic, but their degradation is frequently found to be accelerated in the presence of water microdroplets. The direct chemical consequences of water−oil contact have long been overlooked. We show that aqueous microdroplets in emulsified water− hexadecane (C 16 H 34 ) mixtures can spontaneously produce CO 2 , •H, H 2 , and short-chain hydrocarbons (mainly C 1 and C 2 ) as detected by gas chromatography, electron paramagnetic resonance spectroscopy, and mass spectrometry. This reaction results from contact electrification at the water−oil microdroplet interface, in which reactive oxygen species are produced, such as hydrated hydroxyl radicals and hydrogen peroxide. We also find that the H 2 originates from the water microdroplet and not the hydrocarbon it contacts. These observations highlight the potential of interfacial contact electrification to produce new chemistry.

One-step Formation of Urea from Carbon Dioxide and Nitrogen Using Water Microdroplets

“…We propose that water is the major source for reducing hydrogen. In previous work, electron spin resonance spectroscopy has shown that hydroxyl radicals ( • OH) and hydrogen atoms ( • H) are formed at the gas–water and solid–water interfaces, which strongly supports the recent proposal that Colussi made for hydrogen peroxide formation on the sprayed water microdroplet surface . Interestingly, the endothermicity of electron transfer in bulk water (Δ H = 448 kJ mol –1 ) is reversed at the water interface by the destabilization of the hydrated reactant ions: Δ H hydration (H + + OH – ) = −1670 kJ mol –1 , relative to neutral radical products: Δ H hydration ( • OH + • H) = −58 kJ mol –1 .…”

The emerging chemistry of self-electrified water interfaces

“…However, water oxidation forming the peroxide should also yield a product of water reduction. Nguyen et al 129 proposed that hydrogen is the reduced coproduct of hydrogen peroxide formation and asked for its experimental verification that was recently published, 130 analogous to hygroelectricity. 131 A different mechanism proposed by Colussi identifies the mechanical energy required for droplet formation as the energy source for hydrogen peroxide formation.…”

Charged Microdroplets as Microelectrochemical Cells for CO2 Reduction and C–C Coupling

“…Notably, recent findings indicate the activation of H 2 O to produce active hydrogen species (H*), promoting CO 2 adsorption and hydrogenation . Zare and Jia et al showed that contact electrification at water–oil microdroplet interfaces in an emulsion initially enabled a spontaneous evolution of H 2 and the accumulation of ROS, leading to the oxidative cracking of oil at ambient temperature . Colussi demonstrated that electron transfer (ET) between surface-bound ions (OH S – + H S + ) at water microdroplet interfaces can produce H S • , which further promotes CO 2 reduction .…”