Catalytic Cracking of Isooctane and Carbon Deposition Over Ni Supported On Ceria-Zirconia Catalyst

The development of a durable reforming catalyst capable of converting liquid hydrocarbons into reformate (CO+H₂) onboard a vehicle has long been the goal of the fuel processing community. One of the many challenges facing liquid fuel reforming catalysts is to convert long chain hydrocarbons into reformate without the deposition of deleterious carbon species, which degrade the catalyst both chemically and mechanically. Unlike sulfur poisoning, which would be less of an issue with the introduction of sulfur-free fuels, the deactivation of catalyst caused by carbon deposition reflects the intrinsic properties of catalyst materials that can to some extent be controlled by catalyst formulations and reaction conditions. From the nature of reforming reaction and our previous practices on the analysis of deposited carbon derived from liquid hydrocarbon reforming over Ni-based catalysts, we proposed that the light hydrocarbons (C₁-C₄), which are produced by the cracking of liquid hydrocarbons under reforming conditions, play a very important role on carbon deposition and hydrogen production. However, the role of (catalytic) cracking of hydrocarbons on the carbon deposition during reforming of liquid hydrocarbons is still poorly understood.

In order to better understand and elucidate the role cracking of heavy liquid hydrocarbons on carbon deposition and cracking product distribution, isooctane decomposition over ceria-ziconia supported Ni (Ni/CZO) catalysts was investigated in this work by a thermogravimetric quartz tube reactor, coupled with a FT-IR spectroscopy to on-line analyze the carbon deposition amount and the cracking hydrocarbon products. The carbon-deposited catalysts were characterized by temperature-programmed oxidation and scanning electron microscopy. Experimental results showed that carbon deposition amount and rate, type, and the morphologies were related to decomposition temperatures that affect the conversion of isooctane and the distribution of cracking products. These initial cracking products can undergo secondary decomposition reactions and exert a strong influence on the carbon deposition rate. Furthermore, the carbon deposition derived from isooctane cracking products, such as methane and propene, was also investigated as a function of temperature to elucidate the role of different light hydrocarbons on catalyst deactivation during hydrocarbon reforming.