Insights into Au Nanoparticle Size and Chemical State of Au/ZSM-5 Catalyst for Catalytic Cracking of n-Octane to Increase Propylene Production

The cracking of n -octane to propylene was chosen as a model reaction over gold catalysts supported on ZSM-5. Au/ZSM-5 catalysts with a series of Au particle sizes (6.9–10.6 nm) were prepared through deposition–precipitation in which the catalysts were distinguishable and had uniform-sized Au particles. Au/ZSM-5 catalysts with different Au species were obtained by changing the reduction temperature. The crystallinity, textural parameters, and acidity of Au/ZSM-5 were not destroyed compared with those of virgin ZSM-5 through this preparation approach. The influences of Au particle size and Au species are linked to the catalytic activity and selectivity in catalytic cracking reactions to increase propylene production. Metallic gold was found to be dominant for the cracking reaction, and the Au particle size played an important role in the dehydrogenation reaction to produce propylene. The reaction results of real light diesel oil are consistent with octane cracking where a smaller gold particle size provides a better catalytic activity. The effects of the Au chemical state on the catalytic activity and selectivity were also researched, and the Au 0 species was the dominant Au active site for the cracking reaction. A similar conclusion was also verified in the light diesel oil cracking reaction.