(208d) A Detailed Kinetics Study for 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">A
detailed kinetics study for 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 " times new roman>, 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

normal"> 

justify;text-justify:inter-ideograph;text-indent:.5in;line-height:normal">Over the past decade, natural gas
became one of the cleanest and most promising energy sources for various power
and transportation industries. A drop in natural gas price due to the
discovery of large shale gas reserves and new hydraulic drilling technologies
have helped spur an increase in its production and utilization. While natural
gas is considered to have lower emissions than coal and other liquid fuels, its
incomplete combustion can lead to methane (CH4) slip that is the
main component of natural gas [1-3]. Methane has about 20 times higher global warming potential than
that of CO2 [4], thus the
abatement of CH4 emissions is currently an area of great concern and
focus. Our recent findings showed that Ni/CexZr1-xO2
catalysts have a promising activity towards the complete combustion of CH4,
attributed to a synergistic effect between the active metal Ni and the CexZr1-xO2
support. However, the reaction mechanism of CH4 combustion
over Ni/CexZr1-xO2 catalysts is still not well
understood.

justify;text-justify:inter-ideograph;text-indent:.5in;line-height:normal">Herein, we report a detailed
kinetics study over various 2 wt.% Ni/CexZr1-xO2 (x = 1, 0.83, 0.17, 0) catalysts. The CH4 and O2 concentrations
were varied in the range of 3.3 - 6.67% and 2.7 - 33.3%, respectively. CH4
conversion was maintained to <30% by controlling the reaction
temperature from 375℃ to 425℃. Apparent activation energies (Ea) as
well as reactant partial pressure dependencies in methane combustion were investigated. Three different reaction mechanism models, Langmuir-Hinshelwod, Eley-Rideal,
and Mars-van Krevelen, were used to fit our kinetic data. The Mars-van
Krevelen model showed the best fit with the steady state experimental results. Based
on this model (Fig. 1), CH4 is activated on NiO that is partially
reduced to Ni0 during the reaction of gas phase CH4 with
lattice oxygen. Furthermore, the lattice oxygen from the CexZr1-xO2
support can be transferred to Ni0, resulting into reduction of the CexZr1-xO2
support and reoxidation of Ni0 to NiO. The oxygen vacancies
generated from the oxygen transfer can be refilled by the gas phase oxygen. Determination
of the CH4 combustion mechanism over Ni/CexZr1-xO2
catalysts can guide the rational design of future oxidation catalysts in
many applications, such as natural gas vehicles, turbines, and on-site
production flaring of methane.

.0001pt;text-align:center">

text-align:justify;text-justify:inter-ideograph"> " times new roman>Figure 1.
Schematic for CH4 combustion over Ni/CexZr1-xO2
catalysts based on the Mars-van Krevelen mechanism.

normal">[1]
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normal">[2]
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normal">[3]
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justify;text-justify:inter-ideograph;line-height:normal">[4] 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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