10664 | Chem. Commun., 2017, 53, 10664--10667 This journal is © The Royal Society of Chemistry 2017
Cite this: Chem. Commun., 2017,
53, 10664
Fe
2
O
3
, a cost effective and environmentally friendly
catalyst for the generation of NH
3
– a future
fuel – using a new Al
2
O
3
-looping based technology†
Ye Wu,‡
a
Guodong Jiang,‡
b
Hongbo Zhang,
c
Zhao Sun,
c
Yuan Gao,
a
Xiaoping Chen,
d
Huazhang Liu,
e
Hanjing Tian,
f
Qinghua Lai,
c
Maohong Fan *
c
and Dong Liu*
a
Fe
2
O
3
is found to be a cost-effective and environmentally friendly
catalyst for chemical looping generation of NH
3
– a future fuel. The
optimal Fe
2
O
3
loading on nitrogen carriers, AIN, is 5 wt%. Fe
2
O
3
can reduce the activation energy of the N-desorption step of AIN by
100 kJ mol
1
or B30%.
With the rapid development of the world’s economy, increasing
amounts of conventional fossil fuels including coal, oil and
natural gas are being consumed, which has led to the increase
of CO
2
concentration in the atmosphere and thus climate
change.
1,2
In order to alleviate the environmental challenge,
non-carbon based clean fuels especially H
2
have to be used.
3–5
However, the development of hydrogen energy faces several
limitations. For example, energy-intensive liquefaction is
needed for storing H
2
. In addition, the energy density of H
2
is
lower than conventional gaseous fuels. Therefore, safe and
gaseous fuels with higher hydrogen loading capacities should
be developed. Ammonia or NH
3
meets such requirements.
6–8
More than 90% of the world’s ammonia production currently
uses the Haber–Bosch synthesis (HBS) process developed in 1913.
7
Catalysis plays a key role in Haber–Bosch based NH
3
production.
The majority of HBS catalysts are based on iron and are
promoted by various oxides. The reaction conditions of HBS,
400–550 1C and 200–300 atm, determine the high energy
consumption characteristics of the conversional technology.
Various efforts have been made to overcome this challenge. One
of the recent studies has shown that transition metal-mediated
catalysts with second catalytic sites can be used to alleviate the HBS
reaction conditions to some degree.
8
However, the major barriers
of HBS, high energy consumption resulting from the unfavorable
thermodynamic equilibrium at 400–550 1C and thus the use of this
expensive commodity, and high pressure, cannot be fundamentally
changed. In addition, using methane reforming for H
2
production
in HBS is not sustainable due to the global unsustainability of
CH
4
.
9
Accordingly, people are increasingly interested in exploring
the possibilities of developing inexpensive non-CH
4
NH
3
synthesis
technologies. As an example, Ga ´lvez et al. proposed a two-stage
thermochemical process which is supposed to decrease the energy
requirement and cost needed for NH
3
production.
7,10
This process
starts with an endothermic formation of AlN via the reaction Al
2
O
3
with C in a N
2
atmosphere, followed by exothermically hydrolyzing
AlN for combined NH
3
production and Al
2
O
3
regeneration.
The reactions of the chemical looping ammonia generation (CLAG)
are:
7
3C + N
2
+ Al
2
O
3
- 2AlN + 3CO DH
Y
298
= +708.1 kJ mol
1
(R1)
2AlN + 3H
2
O - Al
2
O
3
+ 2NH
3
DH
Y
298
= 274.1 kJ mol
1
(R2)
Intensive studies on (R1) or the N-sorption step have
been conducted. The major factors affecting (R1) include the
characteristics of carbon, Al
2
O
3
and catalysts, and reaction
conditions. The structure and existing form of Al
2
O
3
affect its
reactivity in (R1). The reactivity of Al(OH)
3
is lower than that of
g-Al
2
O
3
, while it is better than that of a-Al
2
O
3
. The reactivity is
of the order of g-Al
2
O
3
4 Al(OH)
3
c a-Al
2
O
3
.
11
High-quality
catalysts can be used for improving the reaction kinetics of (R1)
a
MIIT Key Laboratory of Thermal Control of Electronic Equipment,
School of Power Engineering, Nanjing University of Science & Technology,
Jiangshu 210094, China. E-mail: ywu@njust.edu.cn; Tel: +86-25-84304232
b
College of Materials Science and Engineering, Nanjing Tech University,
Nanjing 210009, China. E-mail: gdjiang@njtech.edu.cn; Tel: +86-13770930213
c
Departments of Chemical and Petroleum Engineering, University of Wyoming,
WY 82071, USA. E-mail: qlai@uwyo.edu, mfan@uwyo.edu; Tel: +13077665633
d
Key Laboratory of Energy Thermal Conversion and Control of Ministry of
Education, School of Energy and Environment, Southeast University, Nanjing
210096, Jiangsu, China. E-mail: xpchen@seu.edu.cn; Tel: +86-13951898460
e
Institute of Industrial Catalysis of Zhejiang University of Technology, Hangzhou,
310014, Zhejiang, China. E-mail: cuihua@zjut.edu.cn; Tel: +86-13805715584
f
Department of Chemical Engineering, West Virginia University, WV 26506, USA.
E-mail: hanjing.tian@mail.wvu.edu; Tel: +13042939365
† Electronic supplementary information (ESI) available: Details of sample pre-
paration and characterization, N-desorption method, the calculation method of
AlN conversions, and supplementary figures. See DOI: 10.1039/c7cc04742h
‡ Ye Wu and Guodong Jiang are co-first authors because they contributed equally
to the work.
Received 19th June 2017,
Accepted 1st September 2017
DOI: 10.1039/c7cc04742h
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