The
three-way catalyst performances of honeycomb-coated Rh catalysts
were studied on several metal phosphate supports (AlPO4, YPO4, ZrP2O7, and LaPO4) using various simulated exhausts with different air-to-fuel ratios
(A/F). These supports significantly
improved the NO
x
purification (deNO
x
) efficiency under slightly lean conditions
(14.6 < A/F ≤ 15.3) as
compared with conventional Rh/ZrO2 catalysts. The deNO
x
activity exhibited the following sequence
of increasing the mean electronegativity of the supports: ZrO2 < YPO4 < LaPO4 < AlPO4 < ZrP2O7. Although both NO–CO
and NO–C3H6 reactions contributed to
the deNO
x
process, the latter reaction
was more favored on Rh/ZrP2O7 than on Rh/ZrO2. Partially oxidized C3H6 was adsorbed
on Rh/ZrP2O7 in the form of reactive aldehyde
species, in contrast to the less-reactive carboxylate species adsorbed
on Rh/ZrO2. Furthermore, Rh oxide was more easily reduced
to the active metallic state on ZrP2O7 compared
with Rh/ZrO2 when the atmosphere was changed from lean
(A/F > 14.6) to rich (A/F < 14.6). Metallic Rh formed on ZrP2O7 was only slowly oxidized on exposure to excess
O2, whereas Rh on ZrO2 was readily oxidized
to less-active
Rh2O3. The high activity of Rh/ZrP2O7 toward C3H6 oxidation via aldehyde
species as well as the resistance of metallic Rh against reoxidation
are considered to be possible reasons for the enhanced deNO
x
performance of this catalyst in a slightly lean
region.
A stable colloidal sol consisting of CeO2–ZrO2 solid solution (CZ) was studied as an efficient modifier for supported Rh catalysts. After coating CZ sol onto Al2O3 by simple impregnation, the catalytic activity for CO–NO–C3H6–O2 reaction increased to a different extent depending on an air-to-fuel weight ratio (A/F). A significant effect on the activity arises largely from water-gas shift reaction and C3H6 steam-reforming in a rich region (A/F < 14.6), and promoted C3H6–O2 reaction in a lean region (A/F > 14.6). Moreover, CZ coating yielded an oxygen storage capacity (OSC), the effect of which could be highlighted in the catalytic reaction under a dynamic lean–rich perturbation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.