(575j) Catalytic NOx Reduction Using Paper-Structured Catalyst for the Purification of Automobile Exhaust Gas

Air
pollution caused by exhaust gases from combustion engines and systems has
recently become one of the serious environmental issues on a global scale. To
purify exhaust gas, monolithic ceramic honeycombs are widely used as a support
of catalyst components in practical applications; however it has several
disadvantages, e.g. small sideways gas diffusion and low thermal conductivity.
Thus, there has been increasing interest in the new catalytic materials with
micro-meter scale porous structures, which enable the effective gas diffusion
during the catalytic reaction. In our previous works, we have successfully
prepared the Cu/ZnO catalyst powder/inorganic fiber composites, called
paper-structured catalyst, by a papermaking technique. The
paper-structured catalyst possessed a unique fiber-network microstructure and demonstrated
a high catalytic
efficiency and durability as compared with the original catalyst powder in the methanol reforming process for hydrogen production. In
this study, a novel paper-structured catalyst containing Pt/Al₂O₃
powders was prepared aiming at the effective catalytic reduction of nitrogen
oxides (NO_X) in the automobile exhaust gas. Fine powders of Pt/Al₂O₃
catalyst were successfully supported on the ceramic fiber network by a
papermaking technique with a dual polyelectrolyte system; the total retention
of inorganic components reached up to ca. 95%. The paper composite was
flexible, lightweight and easy-to-handle. The ceramic fiber
network tailored in the paper-structured catalyst formed a characteristic
porous microstructure (average pore size: ca. 20 µm,
porosity: ca. 70%). Conversion
efficiency from NO_X to N₂ by using paper-structured
catalyst was superior to those by original catalyst powders,
commercial honeycomb catalyst or pellet-shaped catalyst.
Besides, the paper-structured catalyst demonstrated a quick response in the
catalytic NO_X reduction at a rapid increasing reaction temperature. Loading
of catalyst powders or pellets brought about both poor heat transfer and
heterogeneous gas flow. On the other hand, paper-structured catalyst possessed
a unique micro-porous structure that can promote the effective heat and gas
transfer to the active surfaces, surpassing that of a commercial honeycomb
catalyst. Therefore,
the paper-structured Pt/Al₂O₃ catalyst
is expected to be a promising catalytic material in the practical applications
for the
purification of automobile exhaust gas.