10.1021/cs5020157.s001
Yuki Nagao
Yuki
Nagao
Yunosuke Nakahara
Yunosuke
Nakahara
Takahiro Sato
Takahiro
Sato
Hironori Iwakura
Hironori
Iwakura
Shoya Takeshita
Shoya
Takeshita
Saki Minami
Saki
Minami
Hiroshi Yoshida
Hiroshi
Yoshida
Masato Machida
Masato
Machida
Rh/ZrP<sub>2</sub>O<sub>7</sub> as an Efficient Automotive
Catalyst for NO<sub><i>x</i></sub> Reduction under Slightly
Lean Conditions
American Chemical Society
2015
Rh
reactive aldehyde species
C 3H oxidation
ZrP 2O
ZrO 2
Efficient Automotive Catalyst
YPO
2015-03-06 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Rh_ZrP_sub_2_sub_O_sub_7_sub_as_an_Efficient_Automotive_Catalyst_for_NO_sub_i_x_i_sub_Reduction_under_Slightly_Lean_Conditions/2189014
The
three-way catalyst performances of honeycomb-coated Rh catalysts
were studied on several metal phosphate supports (AlPO<sub>4</sub>, YPO<sub>4</sub>, ZrP<sub>2</sub>O<sub>7</sub>, and LaPO<sub>4</sub>) using various simulated exhausts with different air-to-fuel ratios
(<i>A</i>/<i>F</i>). These supports significantly
improved the NO<sub><i>x</i></sub> purification (deNO<sub><i>x</i></sub>) efficiency under slightly lean conditions
(14.6 < <i>A</i>/<i>F</i> ≤ 15.3) as
compared with conventional Rh/ZrO<sub>2</sub> catalysts. The deNO<sub><i>x</i></sub> activity exhibited the following sequence
of increasing the mean electronegativity of the supports: ZrO<sub>2</sub> < YPO<sub>4</sub> < LaPO<sub>4</sub> < AlPO<sub>4</sub> < ZrP<sub>2</sub>O<sub>7</sub>. Although both NO–CO
and NO–C<sub>3</sub>H<sub>6</sub> reactions contributed to
the deNO<sub><i>x</i></sub> process, the latter reaction
was more favored on Rh/ZrP<sub>2</sub>O<sub>7</sub> than on Rh/ZrO<sub>2</sub>. Partially oxidized C<sub>3</sub>H<sub>6</sub> was adsorbed
on Rh/ZrP<sub>2</sub>O<sub>7</sub> in the form of reactive aldehyde
species, in contrast to the less-reactive carboxylate species adsorbed
on Rh/ZrO<sub>2</sub>. Furthermore, Rh oxide was more easily reduced
to the active metallic state on ZrP<sub>2</sub>O<sub>7</sub> compared
with Rh/ZrO<sub>2</sub> when the atmosphere was changed from lean
(<i>A</i>/<i>F</i> > 14.6) to rich (<i>A</i>/<i>F</i> < 14.6). Metallic Rh formed on ZrP<sub>2</sub>O<sub>7</sub> was only slowly oxidized on exposure to excess
O<sub>2</sub>, whereas Rh on ZrO<sub>2</sub> was readily oxidized
to less-active
Rh<sub>2</sub>O<sub>3</sub>. The high activity of Rh/ZrP<sub>2</sub>O<sub>7</sub> toward C<sub>3</sub>H<sub>6</sub> oxidation via aldehyde
species as well as the resistance of metallic Rh against reoxidation
are considered to be possible reasons for the enhanced deNO<sub><i>x</i></sub> performance of this catalyst in a slightly lean
region.