Probing the kinetic mechanisms of hydrocarbon oxidation by metal oxide particles under extreme conditions

Abstract

To enable carbon capture and storage, there is a significant interest in investigating the role of micron and nano-sized metal oxide particles in enhancing or inhibiting the oxidation of hydrocarbons. These non-catalytic reactions can be desired in chemical processes like chemical-looping and metal combustion or undesired, such as in hot-spot-forming reactions in internal combustion engines. However, initiating hydrocarbon reactions with metal oxides is challenging at low temperatures. Moreover, the critical oxidation pathways between metal oxide particles and hydrocarbons must be better understood. They can be difficult to investigate experimentally, especially under extreme conditions such as in plasma or under high pressure/temperature conditions found in engines. Furthermore, while modeling gas-phase chemistry for hydrocarbons is well developed, non-catalytic reactions between gases and metal oxide particles still need better understanding and insights from quantum chemistry modeling.Chemical kinetic insights into the reactions between hydrocarbons and metal oxides CuO, NiO, MgO, and CaO were investigated through reactive molecular dynamics simulations (ReaxFF) and experiments to address the above challenges. Advanced time-dependent electron ionization molecular beam mass spectrometry (EI-MBMS) techniques were used to gain insights into chemical kinetics and reaction mechanisms under plasma and non-plasma experimental conditions. It was found that plasma could reduce CuO and NiO particles with hydrocarbons at temperatures nearly 200 °C lower than without plasma. In addition, it was computationally shown how Ca-based particles would trigger hot spots and pre-ignition in engine environments while Mg-based particles would not. The overall presented work impacts Chemical-Looping Combustion (CLC) to enable low-carbon energy conversion and the prevention of catastrophic Low-Speed Pre-Ignition (LSPI) in internal combustion engines.