Evaluating the role of hydroxyl keto-hydroperoxide in the low temperature oxidation of alkenes

The low temperature oxidation of alkenes exhibits some distinct reaction pathways that may form differ-ent kinds of keto-hydroperoxides to start the chain-branching by further decomposition. This is mainly due to the existence of the double bond that the OH radical could add to it. This work explores that phenomenon by investigating the low temperature oxidation of three alkenes (1-hexene, 1-heptene and 1-decene) in a jet-stirred reactor (JSR) at atmospheric pressure. The synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) experiments combined with hydrogen-deuterium (H-D) exchange reactions were used to evaluate the chain branching pathways. Alkenyl keto-hydroperoxide (AnKHP) and hydroxyl keto-hydroperoxide (HyKHP) are identified. They represented two different chain branching reaction networks that are initiated from the H-abstraction of the primary and secondary C -Hs and via OH addition to the double bond. The experimental estimated and model predicted ratios of AnKHP to HyKHP are compared, and the result indicates that the literature model underpredicts the chain branching reactions via the formation of AnKHP, but overpredicts the chain branching reactions via HyKHP.(c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.