A major
problem in biomass or coal gasification is removal of syngas
byproducts such as H2S, NH3, and tars (heavy
hydrocarbons) that cause catalyst deactivation and clogging problems
downstream. Rare earth oxides (REOs) doped with transition metals
(TMs) are promising catalysts for tar reforming. With propane as a
model compound, we compared such catalysts to a typical supported
Ni catalyst, and also to recent density functional theory (DFT) results
modeling these systems. The REO/TM catalysts are active over the range
920–1000 K, with no significant deactivation in non-sulfur
containing feeds. In particular, a Mn/CeO2 catalyst showed
good reforming activity with low carbon, CO2, and CH4 yields. This catalyst also maintained some activity in the
presence of 40 ppm H2S. Kinetics calculations showed that
most such catalysts have near zero order kinetics with respect to
water, making them usable with a variety of gasifier effluents. Characterization
of used catalysts by multiple techniques suggests that the metal-doped
REOs do not undergo much (if any) phase separation in extended use
under tar reforming conditions, with Mn- and La-doped CeO2 being especially stable.
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