Comparison of thermal and catalytic cracking of 1-heptene from ReaxFF reactive molecular dynamics simulations

Abstract

Endothermic catalytic cracking of hydrocarbon fuels is one of the most effective methods for thermal management in high-speed jet engines. Despite extensive research, improved understanding of fundamental reaction mechanisms and chemical events associated with hydrocarbon cracking reactions remains desirable. In this investigation, we used the ReaxFF force field to investigate the initial reaction pathways involved in hydrocarbon cracking over amorphous silica, hydrated amorphous silica, and amorphous aluminosilicate nanoparticles. We performed ReaxFF simulations at 1750, 1850, and 1950K on large interface systems (∼2250 atoms) composed of an amorphous silica particle surrounded by 100 hydrocarbon molecules. Hydrocarbon cracking proceeded via complex network of reaction pathways and produced hydrogen and a wide range of saturated and unsaturated hydrocarbon products, consistent with experimental results. Analysis of trajectories from ReaxFF simulations showed complex initiation chemistry for thermal and catalytic cracking of 1-heptene. In general, thermal cracking of 1-heptene was mainly initialed by CC bond scission followed by free radical reaction mechanism, whereas catalytic cracking was predominantly activated by CC bond scission, protonation and dehydrogenation. This work demonstrates that ReaxFF reactive force field can be a useful approach for examining the complex chemistry associated with hydrocarbon cracking.