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

Authors: 
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
catalysts

normal">

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

normal">Abstract

The
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
catalysts.

References:

[1]
Gélin, P., Primet, M., Appl. Catal. B:
Environ.
39: 1-37, 2002

[2]
Mihai, O., Smedler, G., Nylén, U., Olofsson, M., Olsson, L., Catal. Sci. Technol. 7: 3084-3096, 2017

[3]
Roth, D., Gélin, P., Primet, M., Tena, E., Appl.
Catal. A: General 203: 37-45, 2000

" 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

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