Evaluation of Rh-Pyrochlore Coated Monolith for the Reforming of Diesel Fuel

Evaluation of Rh-Pyrochlore Coated Monolith for the Reforming of Diesel Fuel

Daniel J. Haynes¹, David A. Berry¹, Dushyant Shekhawat¹, Mark W. Smith^1,2, Matthew Seabaugh³

¹National Energy Technology Laboratory/US DOE, Morgantown, WV

² URS-Washington Division, Morgantown, WV

³NexTech Materials, Lewis Center, OH

Through its Solid State Energy Conversion Alliance (SECA) program, the U.S. Department of Energy has been in collaboration with industrial partners to sponsor the development of solid oxide fuel cells (SOFCs) for clean and efficient energy production from hydrocarbon-based fuels.  While the applications for fuel cells are numerous, auxiliary power units (APUs) for long haul diesel trucks and military vehicles have been identified as a possible entry point to introduce the technology into the commercial market.  On-board hydrogen production from the reforming of diesel can be used to meet the energy requirements of the SOFC.  However, high levels of sulfur and aromatic compounds commonly found in diesel fuel limit the formation of synthesis gas (H₂ + CO) because they are poisons to traditional reforming catalysts.  The National Energy Technology Laboratory (NETL) has been developing reforming catalysts based on the pyrochlore crystal structure (A₂B₂O₇) to reduce deactivation.  Pyrochlore-based catalysts are of interest primarily due to their chemical stability in high temperature reducing and oxidizing environments.  They also possess the ability to accommodate the substitution of a wide variety of active and promoting metals within the oxide framework.  This distinguishes them from traditional supported metal catalysts, which are more prone to sintering at high-temperatures and have less control of particle size and “next nearest-neighbor interactions”.  Furthermore, oxygen-conducting supports have been shown to greatly improve hydrocarbon reforming with substituted oxide catalysts such as pyrochlores.  In particular, the rate of deactivation is reduced by decreasing the amount of deactivating carbon formed on the catalytically active phase through oxygen transport from the gas phase, through the support to react with strongly adsorbed hydrocarbon species believed to be coke precursors.  Researchers at NETL successfully demonstrated a Rh-substituted zirconate pyrochlore catalyst supported onto zirconium-doped ceria (ZDC) to be active and stable for the reforming of commercial diesel fuel for 1000 hrs under oxidative steam reforming conditions.  Following this test, NETL has been collaborating with NexTech Materials in order to develop an effective process to apply the optimized pyrochlore/ZDC catalyst onto a commercially representative form such as monolith.  A square channel alumina monolith structure coated with an oxygen-conducting support, onto which the active pyrochlore phase was deposited, has been fabricated.  NETL has recently completed a successful 93 hour fuel reforming testing of the commercially representative monolith using commercial diesel fuel.  Synthesis gas yields were stable and near those predicted by equilibrium for the 93 hours time on stream.  No indicators of catalyst degradation (olefin formation, pressure buildup, etc.) were observed when the run was discontinued.