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

Chih-Han  Liu, University at Buffalo

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

Chih Han Liu1, Junjie Chen1, Todd J. Toops2, Eleni A. Kyriakidou1,*

1Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA

2National Transportation Research Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA



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].  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].  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.

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].  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.


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.


[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: LTAT _ Low-Temperature-Storage-Protocol.pdf