| Summary: | 博士 === 國立中央大學 === 化學工程學系 === 85 === The effects of additives (Na2O, K2O, CeO2, and SiO2) on Pd/
Al2O3 and Pt/Al2O3 for CO and HC oxidation were studied in this
work. The objectivesof this work are (1) to improve the CO
conversion on the existing commercialcatalytic converter for a
two-stroke motorcycle and (2) to pursue a methodto improving the
CO conversion on the Pd-containing catalytic converter. The
characterization of the catalysts includes BET surface area,
pore volume, temperature-programmed reduction of hydrogen,
temperature-programmeddesorption of carbon dioxide, and CO
chemisorption. The reactions were performedunder the
stoichiometric and oxygen-deficient conditions. In addition,
theactual performances of the catalytic converters were verified
by the ECE-40 mode driving cycle test. From the experimental
results, one finds that the addition of promoteron Pt/Al2O3 or
Pd/Al2O3 catalyst slightly decreases the surface area and
porevolume of the catalyat but does not markedly change the Pt
dispersion. TheCO2-TPD results reveal that the basicity of the
Pt powder catalyst is in the order: Pt/K2O/Al2O3 ≒ Pt/K2O/CeO2/
Al2O3 > Pt/Na2O/Al2O3 > Pt/K2O/Al2O3-SiO2 > Pt/Al2O3 > Pt/Al2
O3-SiO2. The basicity of Pt/CeO2/Al2O3 or Pt/Al2O3-SiO2 can be
increased by the addition of K2O. In addition, the basicity of
Pt/K2O/Al2O3 added amount of K2O. The order of basicity of the
Pt catalysts can also be applied to the Pd catalysts. Under
the stoichiometric point, the activities of the Pt powder
catalystsfor CO and C3H6 oxidation follow the order: Pt/K2O/Al2
O3 > Pt/Na2O/Al2O3 > Pt/Al2O3 > Pt/Al2O3-SiO2,that is the same
as the order of basicity of these catalysts. The activity of Pt/
K2O/Al2O3 is even higher than Pt/CeO2/Al2O3. Inaddition, the
effect of K2O on activities of Pt/Al2O3 for CO and C3H6
oxidation is affected by the added amount of K2O. In addition,
Pd catalysts exhibit a higher activity than Pt catalysts for CO
and C3H6 oxidation when they are supported on the same support.
Under an oxygen-deficient condition and in the absence of water,
C3H6 conversionson all powder catalysts studied in this work
always increase with increasing reaction temperature.
Nevertheless, the CO conversion shows the reverse trend once
oxygen is completely reacted. Pt/Al2O3 and Pt/Al2O3-SiO2 exhibit
higher C3H6 conversions and lower CO conversions, that is
contrary to Pt/K2O/Al2O3. Moreover, the CO conversion on Pt/Al2
O3 can be promoted by addition of CeO2, Na2O, and K2O. Under
an oxygen-deficient condition and in the presence of water, CO
and C3H6 conversions can be increased by the water-gas shift
(WGS) and steam reforming reactions. Pt/Al2O3 and Pt/Al2O3-SiO2
exhibit higher activities for the steamreforming reaction, while
they exhibit lower activities for the WGS reaction. The addition
of Na2O or K2O on Pt/Al2O3 catalyst can significantly enhance
the WGS reaction. The activities of the catalysts for the WGS
reaction also followthe order of basicity of these powder
catalysts,i.e., Pt/K2O/Al2O3>Pt/Na2O2/Al2O3>> Pt/Al2O3 > Pt/Al2
O3-SiO2. In addition, the promotional effect of Na2O or K2Oon
the Pt/Al2O3 for the WGS reaction is better than that of CeO2.
When Pt and Pdare supported on the same support, CO conversions
on Pd-containing catalystsare significantly lower than those on
Pt-containing catalysts under an oxygen- deficient condition.
Nevertheless, the CO conversion on Pd/Al2O3 can be
significantlyincreased by the simultaneous addition of K2O and
CeO2. The effect od air/fuel ratio on the CO conversion of
the monolithic catalystis significantly greater than that on the
HC conversion. The experimental results reveal that the HC
conversions on PtRh-containing monolithic catalysts follow the
order: PtRh/Al2O3-SiO2 >= PtRh/Al2O3 > PtRh/Al2O3-CeO2 > PtRh/K2
O/Al2O3-SiO2 >PtRh/K2O/Al2O3 > Pt/K2O/Al2O3-CeO2, that is
contrary to the order of the CO conversion.On the other hand,
the CO conversion on the PdRh-containing monolithic catalystis
significantly lower than that of the PtRh-containibg catalyst.
Nevertheless,the difference in CO conversions between PdRh/Al2
O3-CeO2 and PtRh/Al2O3-CeO2 canbe significantly lessened by
adding K2O on the Pd catalyst. The experimental results
verifiy that K2O is a promising additve to the
catalyticconverter for a two-stroke motorcycle. The test results
of the ECE-40 mode drivingcycle reveal that the CO conversions
on PdRh/Al2O3-CeO2 and PtRh/Al2O3-CeO2 can be significantly
promoted by the addition of K2O. The CO conversion PdRh/K2O/Al2
O3-CeO2is close to that PtRh/Al2O3-CeO2 (the existing commercial
catalytic converter for a two-stroke motorcycle). Therefore,
PtRh/K2O/Al2O3-CeO2 can be applied to a two-stroke motorcycle
with the higher CO emission. PdRh/K2O/Al2O3-CeO2 might
substitute PtRh/Al2O3-CeO2 to be used in a two-stroke motorcycle
with the lower CO emission.
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