(755e) Controlled Synthesis of High Surface Area Pd and Pt/SiO2(core)@ZrO2(shell) Catalysts for Low Temperature Oxidation Applications

Authors: 
Liu, C. H., University at Buffalo
Toops, T. J., Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory
Kyriakidou, E. A., University at Buffalo, The State University of New York
Chen, J., University at Buffalo, The State University of New York

text-align:center;line-height:normal">Controlled
Synthesis of High Surface Area Pd and Pt/SiO2(core)@ZrO2(shell)
Catalysts for Low Temperature Oxidation Applications

normal"> 

text-align:center;line-height:normal"> 9.0pt;font-family:" times new roman>Chih Han Liu1, Junjie
Chen1,
Todd J. Toops2, Eleni A. Kyriakidou1,*

text-align:center;line-height:normal">1Department
of Chemical and Biological Engineering, University at Buffalo, The State
University of New York, Buffalo, NY 14260, USA

text-align:center;line-height:normal">2National
Transportation Research Center, Oak Ridge National Laboratory, Oak Ridge, TN
37831, USA

text-align:center;line-height:normal"> font-family:" times new roman>*elenikyr@buffalo.edu

justify;text-justify:inter-ideograph;line-height:normal">Future diesel oxidation catalysts
will need to perform effectively at increasingly low exhaust temperatures; this
so-called “150ºC challenge” (i.e., achieve over 90% conversion below 150oC)
arises from continued improvements in engines efficiency.  Palladium supported
on ZrO2 catalysts have been tested for their low temperature diesel
oxidation performance where 50 and 90% conversions were achieved at 160, 180ºC
for CO and 180, 195ºC for C3H6, respectively [1] " times new roman>.  Uncontrolled incorporation of ZrO2 on
high surface area SiO2, resulted in incomplete coverage of SiO2
by ZrO2, leading to decreased performance compared to Pd/ZrO2
catalysts.  Complete coverage of SiO2 by ZrO2 was thus
introduced and SiO2(core)@ZrO2(shell) supports with an
enhanced surface area of 210 m2/g were synthesized [2] " times new roman>.  Herein, SiO2@ZrO2 supports
with controlled sizes were synthesized by varying the NH4OH
concentration and feed rate, resulting in SiO2@ZrO2
spheres with average diameters of 450 nm and 202 nm (Fig. 1A, B).  The surface
areas of the synthesized SiO2@ZrO2 supports increased with
decreasing SiO2@ZrO2 diameter: 147 and 293 m2/g
for SiO2@ZrO2 supports with 450 and 202 nm diameter,
respectively.

text-indent:.5in">The
catalytic performance of 1 wt.% Pd/SiO2@ZrO2 monometallic
catalysts was evaluated using the Crosscut Lean Exhaust Emissions Reduction
Simulations (CLEERS) protocol (333 mL/min, 12% O2, 6% H2O,
6% CO2, 400 ppm H2, 2000 ppm CO, 100 ppm NO, 250 ppm C2H4,
100 ppm C3H6 ,33.33 ppm C3H8 and
210 ppm C10H22, Ar balance) under degreened and
hydrothermally aged conditions [3] " times new roman>.  Comparable T50’s of CO were observed
over 1 wt. % Pd/SiO2@ZrO2 with 450 and 202 nm support
diameter, while Pd/SiO2@ZrO2 (202 nm) had a lower T50
of THCs by 17oC (Fig. 1C).  Improved performance was achieved after
hydrothermal aging at 800oC/10h, with the T50’s of 1 wt.
% Pd/SiO2@ZrO2 (450 nm) decreasing to 187oC
(CO) and 240ºC (THCs), while even lower T50’s (176oC
(CO), 222ºC (THCs)) were achieved over the smaller support diameter (202 nm) 1
wt. % Pd/SiO2@ZrO2 catalyst.  Monometallic 1.8 wt.%
Pt/SiO2@ZrO2, as well as bimetallic Pd-Pt/SiO2@ZrO2
catalysts with Pd/Pt ratios varying from 1/3 to 3 were synthesized for an
immediate comparison with the performance of 1 wt.% Pd/SiO2@ZrO2
This work illustrates the potential of developing Pd-based oxidation catalysts
with enhanced durability and low-temperature activity using SiO2@ZrO2
core@shell shaped mixed oxide supports with controlled sizes.

text-align:center;line-height:normal">

justify;text-justify:inter-ideograph;line-height:normal">Figure 1.  TEM image of SiO2@ZrO2
supports with (A) 450 nm (B) 202 nm diameters, and (C) T50,90 of 1
wt.% Pd/SiO2@ZrO2 catalysts with 202, 450 nm support
diameters evaluated with the simulated diesel exhaust CLEERS protocol.

justify;text-justify:inter-ideograph;line-height:normal"> 

[1] M.-Y. Kim, E.A.
Kyriakidou, J.-S. Choi, T.J. Toops, A.J. Binder, C. Thomas, J.E. Parks II, V.
Schwartz, J. Chen, D.K. Hensley, Appl. Catal., B, 187, 181-194 (2016).

[2] E.A.
Kyriakidou, T.J. Toops, J.-S. Choi, M.J. Lance, J.E. Parks II, US Patent
Publication US20180250659A1 (2018).

[3] Aftertreatment
Protocols for Catalyst Characterization and Performance Evaluation:
Low-Temperature Storage Catalyst Test Protocol:
https://cleers.org/wp-content/uploads/2018/03/2018_ LTAT _
Low-Temperature-Storage-Protocol.pdf

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