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@PHDTHESIS{Ren:843754,
author = {Ren, Jie},
othercontributors = {Palkovits, Regina and Liauw, Marcel},
title = {{D}esigning highly active and stable {N}i-based catalysts
for methanation of carbon dioxide},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2022-03376},
pages = {1 Online-Ressource : Illustrationen},
year = {2022},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2022},
abstract = {Power-to-Gas (PtG) concept is under discussion as a
technology for storing energy on a large scale as a result
of the fluctuating and locally concentrated availability of
renewable energy sources. Therefore, methanation of CO2 with
renewable H2 (i.e., via electrolysis) is considered
promising due to the fact that it can be integrated in the
existing infrastructure of natural gas and electricity
grids. CO2 methanation is an exothermic and
thermodynamically favorable reaction requiring an effective
catalyst. Ni-based catalysts are widely investigated for CO2
methanation due to their low cost, easy availability, and
comparable activity during the reaction. Nevertheless,
conventional Ni-based catalysts (i.e., Ni/Al2O3) are easily
deactivated due to sintering and coke deposition during the
exothermic methanation reaction. Hence, Ni-based catalysts
with enhanced properties (e.g., special structure, Ni
dispersion, oxygen vacancy, reduction degree) need to be
deeply investigated for providing crucial knowledge for
related researchers. In chapter 2, hydrotalcite-derived
Mg-Al oxides with different morphologies were synthesized
through co-precipitation and used for Ni-based catalyst
preparation. The effect of support morphology on the Ni
dispersion and catalytic activity in CO2 methanation was
investigated. Obtained supports and catalysts were
rigorously characterized by various techniques, determining
crystallite size, Ni dispersion, morphologies, and basic
sites of the materials. The activity, selectivity, and
long-term stability of Ni-based hydrotalcite-derived
catalysts were evaluated for CO2 methanation under different
conditions (i.e., gas hourly space velocities, reaction
temperatures, and reduction temperatures). Based on the
results, Mg-Al hydrotalcites prepared under solution pH of
10 and aging temperature of 20 oC (MAH-10) supported 20
$wt\%$ Ni, with a “rosette-like” structure, exhibited
remarkable CO2 conversion $(83.5\%),$ CH4 selectivity
$(99.4\%),$ and turnover frequency (TOF) of 13.5 min−1 at
400 °C. This superior activity of Ni/MAH-10 was attributed
to its high basicity, optimized pore size, and defined
support structure, which resulted in a high Ni dispersion
and metallic surface area after reduction. In chapter 3,
novel La2-xCexNiO4 perovskite-derived catalysts were
prepared by a sol-gel method, and various characterization
techniques were employed to understand structure-performance
relationships in CO2 methanation. Based on the
characterization results of La2-xCexNiO4 catalysts,
La0.5Ce1.5NiO4 with a La/Ce ratio of 0.5/1.5 and 11 $wt.\%$
Ni was found to have tailored basicity, reducibility, oxygen
vacancies, better Ni dispersion, and larger Ni (111) crystal
plane, which therefore exhibited the highest CO2 conversion
rate of 57.4 mmolCO2/molNi/s and $99.8\%$ CH4 selectivity at
350 °C. In agreement with the properties obtained from
characterization, in-situ DRIFTS experiments confirmed CO2
methanation over La0.5Ce1.5NiO4 to proceed via CO
hydrogenation. At last, the results obtained in this chapter
suggest that both basicity and oxygen vacancy content
contribute to the outstanding catalytic performance and
stability during CO2 methanation. To know the influence of
the preparation method, the activity and structure of
Ni/(La, Ce)Ox and La0.5Ce1.5NiO4 were compared (in chapter
4). The results demonstrate that Ni/(La, Ce)Ox prepared by
impregnation possess a smaller particle size but less Ni
(111) crystal plane than La0.5Ce1.5NiO4, which therefore
show low activity and stability in CO2 methanation. In
chapter 5, the effects of impurities (i.e., N2, steam, and
O2) on the activity of CO2 methanation over Ni/ZrO2 were
carefully studied. The reducible ZrO2 supporting Ni favors
the formation of oxygen vacancy, which enhance CO2
adsorption and subsequent hydrogenation into methane.
Interestingly, it was found that trace O2 enhanced CO2
methanation over Ni/ZrO2 due to the generation of more *OH
groups, which facilitate the conversion of the intermediates
to methane. In summary, the various Ni-based catalysts were
fabricated through different methods, and the activity was
carefully investigated. Through the advanced
characterizations, the effects of metal-support interaction,
reaction conditions, preparation method, and the impurities
on the CO2 methanation were elucidated. This thesis gathers
important findings on Ni-based catalysts design, which are
crucial to advance the CO2 methanation in PtG technology.},
cin = {155310 / 150000},
ddc = {540},
cid = {$I:(DE-82)155310_20140620$ / $I:(DE-82)150000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2022-03376},
url = {https://publications.rwth-aachen.de/record/843754},
}
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