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(755d) Small Pore Zeolite SSZ-13 Supported Pd As Highly Stable Low-Temperature Methane Combustion Catalysts

Gao, F., Pacific Northwest National Laboratory
Cui, Y., Pacific Northwest National Laboratory
Peng, B., Pacific Northwest National Laboratory
Kovarik, L., Pacific Northwest National Laboratory
Wang, Y., Washington State University

Meng Gao, Feng 2 38 2019-03-12T22:15:00Z 2019-03-12T22:15:00Z 1 396 2263 PNNL 18 5 2654 15.00

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" times new roman>Small pore zeolite
SSZ-13 supported Pd as highly stable low-temperature methane combustion


mso-char-indent-count:1.0">Yanran Cui, Bo Peng, Libor Kovarik, Yong Wang, Feng Gao* " times new roman text1>

0in;margin-left:0in;margin-bottom:.0001pt"> font-family:" times new roman minor-fareast>Institute
for Integrated Catalysis, " times new roman>Pacific Northwest
National Laboratory

mso-char-indent-count:1.0">Richland, WA 99352, USA

*Corresponding author: " times new roman> feng.gao@pnnl.gov


low-temperature catalytic combustion of methane has been extensively studied
for reducing methane emissions from lean-burn natural gas engine exhausts. Pd
supported on Al2O3 has been known to be the most active,
and therefore, the most commonly used catalyst for this application [1].
However below ~450 ºC, water vapor in engine exhausts severely deactivates this
catalyst [2]. The deactivation has been attributed to transformation of the
active PdO phase, e.g., sintering or the formation of an inactive Pd(OH)2
phase, or hydroxyl group accumulation on the alumina supports [3, 4].   

In this work, hydrothermally
stable small pore SSZ-13 zeolites are used as the PdO support. Si/Al ratios of
the supports are systematically varied from 6 to 36 to manipulate support
hydrophobicity, which is found to play a decisive role in Pd dispersion. For a
hydrophilic support at Si/Al = 6, Pd largely presents as atomically dispersed
cations in zeolite exchange positions. By increasing Si/Al ratio to increase
support hydrophobicity, Pd progressively occupies zeolite external surfaces as
PdO particles. Pd/SSZ-13 catalysts with Si/Al = 6 and 12 still suffer from
water-induced deactivation, the same as the Pd/Al2O3
reference catalyst studied here; at Si/Al ratios of 24 and 36, however, the
Pd/SSZ-13 catalysts become much more stable than Pd/Al2O3
in the presence of water vapor. To obtain insights into the stability
improvement of these latter Pd/SSZ-13 catalysts, detailed low-temperature methane
combustion kinetics are conducted. For Pd/Al2O3, the powder-law
dependence on H2O partial pressure is found at -1, fully consistent
with the inhibiting role of water vapor. For the Pd/SSZ-13 catalysts (Si/Al =
24 and 36), the ~0 powder-law dependence on H2O pressure explains
their improved stability. It is concluded that hydrophobicity of the support
plays a key role in promoting the stability and activity of methane combustion


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" times new roman>[4] Schwartz, W. R., Ciuparu, D.,
Pfefferle, L. D., J. Phys. font-family:" times new roman>Chem. C 10.5pt;font-family:" times new roman>116: 8587-8593, 2012