(134b) 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.