(758e) Complete Methane Combustion over Ni/CexZr1-XO2 catalysts

Authors: 
Chen, J., University at Buffalo, The State University of New York
Carlson, B., University at Buffalo, The State University of New York
Choi, J. S., Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory
Li, Z., Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory
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

text-align:center;line-height:normal">Complete methane combustion over
Ni/CexZr1-xO2 catalysts

text-align:center;line-height:normal"> font-family:" times new roman> 

text-align:center;line-height:normal"> 9.0pt;font-family:" times new roman>Junjie Chen1, Benjamin
D. Carlson1,
Jae-Soon Choi2, Zhenglong Li2, 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;text-indent:.5in;line-height:normal">As the push for alternative energy
sources grows, natural gas has become a promising, significantly cleaner
burning resource compared to traditional fossil fuels.  Methane (CH4),
as the main component of natural gas, has about 20 times higher global warming
potential compared to CO2 [1].  Thus, unburnt CH4
emissions from combustion engines or turbines have attracted significant
attention.  Although Ni/CeO2-ZrO2 has been shown to be an
effective catalyst for CH4 reforming reactions, the development of
Ni/CeO2-ZrO2 catalysts that are highly active for the
oxidation of CH4 has been poorly investigated.  [17] " times new roman>The goal of this work is to develop a fundamental
understanding of the synergistic effect between the active metal (Ni) and a
series of ceria-zirconia redox supports, as well as the impact of the oxygen
storage capacity (OSC) of CexZr1-xO2 supports
on the CH4 combustion performance.

justify;text-justify:inter-ideograph;text-indent:.5in;line-height:normal">CexZr1-xO2
(x=1, 0.83, 0.5, 0.17, 0) supports were synthesized by co-precipitation.  Nickel
was deposited on the as-synthesized supports by dry impregnation.  The textural and redox properties
of the synthesized 2 wt.% Ni/CexZr1-xO2catalysts were
characterized by N2 physisorption, STEM, EDS, XRD, Raman, H2-TPR
and O2 pulse chemisorption.  The
CH4 oxidation performance of both CexZr1-xO2
supports and 2 wt. % Ni/CexZr1-xO2 catalysts was
tested under a feed gas ratio of CH4: O2: Ar = 1: 5: 9, with
30 sccm total flow (90,000 h-1).  The main low-temperature reduction
peak data of 2 wt.% Ni/CeO2 is centered at
214oC (Fig. 1a) and is assigned to NixOy reduction. 
Zirconia doping led to shifting of the NixOy reduction
peak higher temperatures. Specifically, the NixOy
reduction temperature increased with increasing Zr doping as follows: Ni/CeO2
(214℃) < Ni/Ce0.83Zr0.17O2 (235℃)
< Ni/Ce0.5Zr0.5O2 (264℃) < Ni/Ce0.17Zr0.83O2
(293℃) < ZrO2 (401℃).  Additionally, the CH4
oxidation performance of 2
wt.% Ni/CexZr1-xO2
catalysts (Fig. 1b) followed the same trend as the NixOy reduction
temperature, with the 2 wt.% Ni/CeO2 outperforming (T50 =
54℃, T90 = 72 oC) the 2 wt.% Ni/ZrO2
catalyst.  There results indicate that enhancing the support OSC by Zr doping (ZrO2
(1.9 μmol/g) < CeO2 (33.7 μmol/g) < Ce0.17Zr0.83O2
(41.3 μmol/g)  < Ce0.83Zr0.17O2 (75.7
μmol/g) < Ce0.5Zr0.5O2 (119.7
μmol/g) ) does not enhance the CH4 oxidation performance,
indicating that only the surface or sublayer oxygen species of the catalyst
participate in the lean CH4 combustion.  Although Zr doping does not
improve the CH4 oxidation performance of Ni/CeO2, it
enhances the thermal stability of the catalyst.  Three consecutive CH4
oxidation cycling experiments over Ni/CexZr1-xO2
showed that Zr containing catalysts have better thermal stability than 2 wt.% Ni/CeO2.
Combining the redox properties and methane combustion performance of CexZr1-xO2
and Ni/CexZr1-xO2 catalysts, a dual-site
methane combustion mechanism was proposed as well as a promotion effect between
nickel and ceria-zirconia supports.

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

line-height:105%">Figure 1. " times new roman> H2 –TPR (a) and CH4
combustion performance as a function of inlet temperature (b) of 2 wt.% Ni/CexZr1-xO2
catalysts and 2 wt.% Ni/Quartz sand.

line-height:105%"> " times new roman> 

line-height:105%"> " times new roman>[1]    Peng, H.,
Rao, C., Zhang, N., Wang, X., Liu, W., Mao, W., Han, L., Zhang, P. and Dai,
S., Angew. Chem. lnt. Ed., 2018.

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