Ferrite catalysts derived from electroplating sludge for high-calorie synthetic natural gas production

Article abstract of DOI:10.1016/j.apcata.2017.01.022

In this study, a ferrite catalyst has been prepared through a facile hydrothermal method using industrial Zn and Fe-rich electroplating sludge as raw materials and utilized for the first time as an efficient catalyst for methanation of syngas. The ferrite catalyst showed pretty good catalytic performance during the stability test at 340?°C for 300?h, meanwhile exhibited a higher resistance to thermal shock (600?°C for 12?h) than that of the catalyst prepared from pure chemical reagents or commercial methanation catalyst. More importantly, a high-calorie natural gas with heating value of 41.73?MJ?Nm^?3could be obtained via methanation of syngas over the ferrite catalyst derived from electroplating sludge. Thus, this work provides some new insights for utlising solid waste as raw material for methanation catalyst, which is very cheap.

Full text of DOI:10.1016/j.apcata.2017.01.022

Accepted Manuscript
Title: Ferrite catalysts derived from electroplating sludge for
high-calorie synthetic natural gas production
Authors: Min Chen, Jizhi Zhou, Jia Zhang, Juan Zhang, Zheng
Chen, Jian Ding, Fanhua Kong, Guangren Qian, Jiangang
Chen
PII:
S0926-860X(17)30040-6
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2017.01.022
APCATA 16133
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
26-9-2016
20-1-2017
26-1-2017
Please cite this article as: Min Chen, Jizhi Zhou, Jia Zhang, Juan Zhang, Zheng Chen,
Jian Ding, Fanhua Kong, Guangren Qian, Jiangang Chen, Ferrite catalysts derived
from electroplating sludge for high-calorie synthetic natural gas production, Applied
Catalysis A, General http://dx.doi.org/10.1016/j.apcata.2017.01.022
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Highlights

Ferrite catalysts were synthesized from electroplating sludge by hydrothermal
process.



Electroplating sludge derived catalyst can produce higher heating value of SNG.
Electroplating sludge derived catalyst resist thermal shock perfectly.
Electroplating sludge derived catalyst was more stable and kept intact after
reaction.

Ferrite catalysts prepared from electroplating sludge are used to produce
high-calorie SNG. This method can recycle heavy metals and eliminate the
environmental pollution.

Ferrite catalysts derived from electroplating sludge for high-calorie
synthetic natural gas production
Min Chen,a,b Jizhi Zhou,a Jia Zhang,a Juan Zhang,b Zheng Chen,b Jian Ding,b Fanhua
Kong,c Guangren Qiana* and Jiangang Chenb†
a College of Environmental Engineering, Shanghai University, 333 Nanchen Road,
Shanghai 200444, PR China.
b State Key Laboratory of Coal Conversion, Shanxi Institute of Coal Chemistry, Chinese
Academy of Sciences, Taiyuan 030001, Shanxi, PR China.
c PetroChina Petrochemical Research Institute, Beijing 100195, PR China.
Abstract
In this study, a ferrite catalyst has been prepared through a facile hydrothermal
method using industrial Zn and Fe-rich electroplating sludge as raw materials and
utilized for the first time as an efficient catalyst for methanation of syngas. The ferrite
o
catalyst showed pretty good catalytic performance during the stability test at 340 C
for 300h, meanwhile exhibited a higher resistance to thermal shock (600 oC for 12 h)
than that of the catalyst prepared from pure chemical reagents or commercial
methanation catalyst. More importantly, a high-calorie natural gas with heating value
of 41.73 MJ·Nm-3 could be obtained via methanation of syngas over the ferrite
catalyst derived from electroplating sludge. Thus, this work provides some new
insights for utlising solid waste as raw material for methanation catalyst, which is
very cheap.
Key words； electroplating sludge, ferrite，methanation, high-calorie SNG.
*Corresponding author: E-mail: grqian@shu.edu.cn
†Corresponding author: Email: chenjg@sxicc.ac.cn

1. Introduction
With the development of electroplating industry, sludge generated from
wastewater treatment plants increases, especially in the developing countries, such
as China, electroplating factories produce approximately 10 million tons of
electroplating sludge annually [1]. Since the sludge is enriched in heavy metals such
as Ni, Zn, Fe, Cu, Cr and Cd etc., it is hazardous to environment, as toxic metals
posing a potential risk to the soil and groundwater. Currently, several methods have
being used to dispose the electroplating sludge and the most popular methods are
landfill or metal recovery by suitable technologies [2]. Landfill is not environmentally
benign and may cause large amount of waste of valuable metals [3], thus, it is very
promising to maximize the recovery and reusing of heavy metals economically.
Last decades witness a fairly rapid development of recovery of heavy metals
from electroplating sludge, such as ion exchange, leaching-solvent and membrane
separation, etc. However, these traditional methods have certain obvious drawbacks,
including complicated separation process, high capital cost and relatively low
recovery. Recently ferrite inclusion becomes more and more popular as a novel
treatment to reuse electroplating sludge. During the process heavy metal ions (Mn2+,
Cu2+, Ni2+, Zn2+, Co2+, Fe3+, Al3+ or Cr3+) which match well with the ferrite texture can
be fixed in the crystal lattice of spinel ferrite [4]. Generally, prepared ferrites are
tentatively used as functional materials. Nonetheless, the heavy metals are well
known to be the main elements of heterogeneous catalysis. For instance, Ni, Zn, Cr,
Mn, etc. in ferrite are used as promoters to enhance the efficiency or control the
selectivity of hydrocarbon production in CO hydrogenation [5-7].
As is known, natural gas is an excellent energy carrier due to low carbon release,
advantageous combustion, the existing pipeline grid for transportation and
distribution. It is also used as resources of high purity hydrogen for chemical industry
(trace carbon monoxide present in H2-rich gases) such as NH3 synthesis and methanol
production [8]. In order to extend the application of natural gas as town gas, it is
extremely important to improve the heat value. For example, Japan and South Korea

import liquefied natural gas (LNG) with high heating value typically in a range
between 41 and 46 MJ·Nm-3 [9]. Since Sabatier et al. discovered the hydrogenation of
CO to methane, named methanation (Eq. (1)), the technology had been widely
developed and applied to produce synthetic natural gas (SNG). However, side
reactions water-gas shift (WGS: Eq. (2)) occurs along to certain degree when the
syngas is introduced. The stoichiometric ratio of H2/CO will changed according to the
percent of two component reactions.
3H2 + CO → CH4 + H2O
CO + H2O → CO2 + H2
ΔH 298 = −206 kJ·mol−1
ΔH 298 = −41.1 kJ·mol−1
(1)
(2)
Nonetheless, the selectivity of CH4 and CO2 represents the degree of
methanation and WGS reaction, respectively. WGS reaction is undesirable in
producing high-calorie SNG process, and should be suppressed to reduce the
selectivity of CO2 because higher CO2 content yields SNG of lower heating value. In
consequence, mediate selectivity of CH4 and C2+ hydrocarbons with low CO2 content
is primary. Nickel is the most selective methanation catalyst and displays little activity
for WGS reaction [10]. However, Iron catalysts are known to hold high
Fischer-Tropsch synthesis activity with a low selectivity towards methane [11]. That is
the reason why Ni-Al2O3 cannot produce high calorie SNG like Fe contained catalysts.
Typical performance of Ni catalyst was reports by Dennis, which presented the
highest CO conversion and CH4 selectivity about 80% and 85% with few CO2 during
o
o
the temperature range of 220-380 C [10]. Lee et al. reported at 300 C syngas
methanation (81.7-98.2% CO conversion) produced the high-calorie SNG which
contained 22-33% CO2, 18-27% CH4 and 36-40% C2-4 by using a series of Fe-Zn
catalysts [9].
Using syngas generated from carbon sources (coal, biomass, coke oven gas,
municipal solid waste, etc.) to produce SNG has been considered as a promising way
towards the sustainable development and clean utilization of coal in China, whose
energy consumption has to depend mainly on coal [12]. For instance, the remote
coal resource in west of China could be converted into SNG and transported to
consumer city in East by ready SNG pipeline. Nowadays the heating value of SNG can

be enhanced by producing additional C2-C4 hydrocarbons whose heating value
exceed about 40 MJ·Nm-3(i.e. CH4: 37.85 MJ·Nm-3; C2H6: 67.33 MJ·Nm-3；C2H4: 61.42
MJ·Nm-3; C3H8: 97.19 MJ·Nm-3; C3H6: 90.61 MJ·Nm-3; n-C4H10: 128.68 MJ·Nm-3; C4H8:
121.69 MJ·Nm-3) during methanation [9, 13, 14]. The most popular methanation
catalyst is Ni supported on Al2O3. However, it yields less ethane or propylene. Among
the various catalysts in CO hydrogenation, Fe is reported to produce light paraffin as
most efficiently catalyst and Zn is always used to improve the selectivity of paraffin
[15-17]. Besides, Mn as promoter can also enhance the yield of C2-C4 and decrease
the selectivity of methane [14]. Since diversify metal ions exist in ferrite prepared
from electroplating sludge, it is anticipated that the ferrite might produce more C2+
hydrocarbons and then high-calorie SNG. Moreover, the spinel structure might be
more stable on condition of heat shock in methanation reactor, which is critical to
operate stably [18].
In this work, ferrite catalyst prepared from electroplating sludge (catalyst A) was
tested in a methanation reaction in a fixed bed reactor to produce high-calorie SNG.
For purpose of comparison, Ni-Zn ferrite (catalyst B) made by pure chemical reagents
and industrial catalyst Ni-Al2O3 (catalyst C) were also evaluated by methanation
reaction. Catalytic performance of these catalysts for syngas methanation at different
temperature was studied. Besides, catalytic performance was also retested after high
temperature processing. Results showed that catalyst A exhibited good activities to
produce high-calorie SNG. Meanwhile, this catalyst could suppress water gas shift
reaction significantly. What is more, it showed the slightest drop of activity upon the
heat-treatment.
2. Experimental section
2.1 Catalyst preparation
Electroplating sludge, which were directly collected from Taizhou electroplating
company, Zhejiang province, China, S1 (Zn-rich) and S2 (Fe-rich) contained 80.78 and
56.12 wt% of water, respectively. The electroplating wastewater of S1 and S2 were
separately collected from two workshops (S1 : corrosion protection by Zn of an
object; S2 : pickling). The transformantion of the electroplating waste water into

electroplating sludge follow the treatment process shown in Fig. 1. As listed in Table
1, the main heavy metal elements were Zn (22.2 wt%) and Fe (23.9 wt%). The
chemical reagents, such as Fe(NO3)3·9H2O, Zn(NO3)2·6H2O, Ni(NO3)2·6H2O, NaOH,
HNO3 were all of analytical grade and purchased from Sino pharm Group Chemical
Reagent Co. Ltd., China. Industrial catalyst J101 was purchased from Nanjing
Chemical Catalyst factory.
2.2 Ferrite preparation via hydrothermal treatment
Catalyst A was prepared by hydrothermal method in typical synthesis using
electroplating sludge. In the first step, electroplating sludge from S1 (7.9g) and S2 (5g)
were dissolved in a solution of deionized water (300.0 mL) to form heterogeneous
slurry by stirring in a 500 mL high-pressure autoclave. The amount of Iron additive
(iron scrap) was determined by stoichiometric formula of ferrite and the sludge
composition. NaOH was used to keep the pH of reaction mixture at 9.0~9.5. Next,
o
the autoclave was heated at 180 C for 6 h. Resulting precipitate was collected by
centrifugation, washed with distilled water to remove any impurities and dried at
105 oC for 15 h after the autoclave cooled to room temperature. At last, the catalysts
were calcined at 950 oC for 4 h in muffle. The simulation catalyst B was prepared by
chemical regent using Fe(NO3)3·9H2O, Zn(NO3)2·6H2O and Ni(NO3)2·6H2O in the same
process as catalyst A. Catalyst C J101 was purchased from Nanjing Chemical Catalyst
factory. The catalyst B and C were designated to make comparisons with catalyst A in
the methanation reaction.
2.3 Characterization
X-ray diffractometer was employed to analyze the XRD profiles of as-obtained
ferrites and spent catalysts. The XRD patterns were acquired on a DX-2700
diffractometer with monochromatic Cu Kα radiation (λ = 0.15418nm) operating at 40
kV and 30 mA at a scanning speed of 4°·min-1 in 2θ = 5-80°. The metal compositions
in sludge and as-obtained ferrites were determined by inductively coupled plasma
optical emission spectrometer (ICP-OES, Optima2100DV, PerkinElmer) after the
suitable treatment. Temperature-programmed reduction (TPR) was carried out in a
quartz tube reactor loaded with about 20 mg of freshly calcined powder catalyst by

glass wool to study the reducibility of the catalysts. Silica gel desiccant and 5A
molecular sieve were applied to purify effluent. The TPR experiments were
performed in a mixture gas of 5% H2/N2 at flow rate of 50 mL·min-1. The quartz tube
reactor was heated at a linear programmed rate of 10 °C·min-1 from room
temperature to 1000 °C and the consumption of H2 in the process of TPR was
monitored by comparison of the thermal conductivity difference between the
reference and the product gas. Nitrogen physisorption isotherms were obtained with
a Micromeritics TriStar II 3020 instrument to measure BET surface area, pore volume
and average pore diameter of the fresh catalysts. Prior to analysis, each sample was
outgassed at room temperature for 24 h to remove the moisture and other
adsorbates. The morphology of as synthesized samples was monitored by using
scanning electron microscope (SEM, Zeiss Supra 55). Temperature programmed
oxidation (TPO) measurements was carried out on a 2 mm (I.D.) quartz tube. 30 mg
of used catalysts were placed between two quartz wool plugs and heated from
o
o
ambient temperature to 1000 C at 10 C·min-1 under 10% O2/He stream. Produced
carbon dioxide was measured on-line by the GC. Furthermore, for comparison
purposes, mechanical mixture of 5mg carbon and 25mg fresh catalyst A was also
tested as reference material.
2.4 Catalyst testing
Methanation reaction was carried out in a 1.2 cm (O.D.) stainless steel fixed-bed.
In a typical run, catalysts with grain size ranging in 60−80 mesh were placed between
three layers of quartz sands in the bed. In order to facilitate the heat transfer and
prevent hot spots resulting from the exothermal character of the reaction, the
calcined 1.0 mL catalysts (1.2g of catalyst A) were diluted with 1 mL quartz sands in
the same size. Bed temperature controlled by a temperature controller was
monitored axially using a type-K movable thermocouple which was buried in the
catalytic bed. Before the reaction, catalysts were activated on-line in a stream of
o
hydrogen at 400 C for 6h at atmospheric pressure with a heating rate of 1 °C·min-1.
Then the pressure was elevated to 2.0 MPa by feeding the syngas mixture (H2/CO = 2)
from the pressurized manifold via individual mass flow controller. The gas hourly

space velocity (GHSV) was set at 3000 h−1. Subsequently, it was heated to the desired
reaction temperature by steps of 1 °C·min-1. Catalyst samples were activated in
synthesis gas at 2 MPa by increasing the temperature from 280 oC to 360 °C. Catalytic
performance and thermostability were further investigated after high-temperature
treatment processing (that is, 600 oC for 12 h). Heavy hydrocarbons were collected by
a heated trap (at 130 °C and reactor pressure) placed immediately below the reactor.
Products like water and oil were collected by a cold trap placed after the heated trap.
The tail gas and reactant were analyzed on line by gas chromatographs (Shanghai
Haixin GC-950) equipped with a thermal conductivity detector and a flame ionization
detector. And the gas chromatographs worked with a packed column (TDX-101)
filled with carbon molecular sieve. Quantitatively of products were determined by
calibrated area normalization; accordingly, the CO conversion and product selectivity
were calculated on the basis of the equations.
3. Result and discussion
3.1 X-Ray diffraction (XRD)
Fig. 2a and b showed the XRD patterns of the fresh catalysts. As seen in Fig. 2a,
the peaks at 18.5°, 30.3°, 35.7°, 43.3°, 53.7°, 57.1°, 62.7° and 74.2° of ferrite were
apparent in catalyst A though a few peaks ascribed to impurity were also exist. Most
importantly, these typical diffraction peaks of ferrite matched well with (Ni, Zn)Fe2O4
(PDF 08-0234) [19], which indicated that ferrite with the spinel structure was
successfully synthesized from sludge by the hydrothermal method [20, 21]. The
impurity peaks (Fig. 2a) at the value of 2θ equal to 18.6°, 30.7°, 36.1°, 37.8°, 43.9°,
54.5°, 58.1° and 63.8° were assigned to another form of Fe2SiO4 phase (PDF 44-1385).
All peaks (Fig. 2b) observed at 18.3o, 30.1o, 35.4o, 43.0o, 53.4o, 56.9o, 62.5o, and 74.0o
could be corresponded to (Ni, Zn)Fe2O4 suggesting that the ferrite from reagent was
pure phase.
In order to figure out the phase transformations after the methanation reaction,
the XRD patterns of the used catalysts were depicted in Fig. 2. Fig. 2c showed spent
catalyst A almost maintained the spinel feature, which still matched well with (Ni,
Zn)Fe2O4 and Fe2SiO4 after the whole reaction [22-24]. For the spent catalyst B, the

most intense reflections at 2θ of 35.5°, 40.0°, 42.6°, and 45.0° (Fig. 2d) represented
the characteristic peaks of Fe5C2 (PDF 20-0508) which was known as catalytically
active phase for Fischer-Tropsch synthesis [25]. Additionally, peaks corresponding to
ZnO and Ni were observed in Fig. 2d. This result meant that the spinel phase in
catalyst B was not so stable as that in catalyst A. This difference might be due to the
impurity elements in sludge. For instance, addition of silica could enhance the
stability of iron-based catalyst during Fischer–Tropsch synthesis [26-30]. Though the
formation of Fe2SiO4 inhibited the reduction of iron oxide or carburization of catalysts,
it increased the selectivity of light hydrocarbon [31, 32].
Lee et al. reported that ZnFe2O4 could inhibit sintering of catalyst A during
methanation reaction and thermal treatment [33]. Mn could improve the surface
acidity and enhance carbon-rich environment on the surface of the catalyst A, which
leaded to the increase of the selectivity of C2-C4 [14]. By providing H2 dissociation
sites, Cu increased the reduction ability of Fe2O3 to Fe3O4 and the rate of
carburization. Thus, the content of CH4 and paraffin increased in FTS products [33,
34]. With above knowledge, promoting elements such as Zn, Mn, Cu, etc. in sludge
were likely to produce the higher heating-value SNG and make catalyst more stable.
They might affect the FTS performance individually or jointly [34]. Therefore the
effect of catalyst A was a composite promotion and further study is essential to
confirm the influence of individual element.
3.2 Inductively coupled plasma optical emission spectrometer (ICP-OES)
The mass fractions of different elements in catalysts were analyzed using
ICP-OES. Table 2 showed that the contents of Zn and Ni were almost the same in
catalyst A and B. The several extra elements such as Cu, Al, Cr, and Mn in catalyst A
might as structural promoter to promote the reaction of methanation. Catalyst C was
consisted of Ni and Al, with the content of 21.0 % and 23.30 %, respectively. Since Ni
supported on Al2O3 was a typically methanation catalyst we speculated that catalyst
C would show highest selectivity of methane.
3.3 Temperature-programmed reduction (TPR)
The TPR characterization was used to obtain information about the reduction

behavior of catalysts (Fig. 3). Fig. 3a showed a small H2 consumption peak in the
range of 290-310 oC which might be assigned to be the reduction of CuO to Cu. Then
o
the second one at about 335 C was related to the reduction of Ni2+ to Ni. The third
o
peak appeared in a wide range of 400-550 C was ascribed to the reduction of Fe2O3
o
to Fe3O4. The forth broad peak observed in range of 550-770 C was associated with
Fe3O4 to FeO and the last higher than 850 oC was due to conversion of FeO to Fe [35,
36]. Fig. 3b showed a characteristic curve with four peaks of catalyst B in the H2-TPR
spectra. The first hydrogen consumption weak peak was attributed to the conversion
o
of Ni2+ to Ni. The following peaks which appeared at about 375, 400, 500 and 700 C
could be assigned to the following consecutive reduction of the catalyst B: Fe2O3 →
Fe3O4 → FeO → Fe. A similar tendency was also discovered for the nickel ferrite
catalyst by Löfberg et al. [35]. In Fig. 3c, the higher and broader small shoulder at
about 400 oC was attributed to reduction of bulk nickel oxide [37].
These observations suggested that the reduction of Fe2O3 in catalyst B was
easier than catalyst A. That was, the presence of Fe2SiO4 which led to the Fe2O3
reduction more difficult [18]. The results were in agreement with the conclusion
from the X-Ray diffraction. Catalyst C showed the lowest temperature of the
reduction of NiO. The facilitated reduction of NiO in catalyst C was attributed to its
supporting structure.
3.4 N2-adsorption-desorption measurements
Catalyst nanoparticles were analyzed by Brunauer–Emmett–Teller (BET)
measurement. The BET surface area value of the catalyst A calculated from N2
isotherms was 12.9 m2·g-1, however, catalyst B was 5.8 m2·g-1. Obviously, catalyst A
was about 2 times that of catalyst B. It had been reported that the BET surface area
of the iron catalysts could be increased by silica incorporation [28, 30]. Besides, the
elevated surface area of catalyst A could be partially contributed to some impurity
phase (Fe2SiO4) in XRD [38].
Nitrogen-desorption-adsorption isotherms described the textural analyses of
the catalysts in Fig. S1. According to IUPAC classification, all N2 isotherms were type
IV. The pores had uniform size with an evident hysteresis H3 loop in the 0.8–1.0

range of relative pressure, clearly related to nitrogen capillary condensation. These
indicated that catalysts were characteristic of mesoporous materials with regard to
mean pore-size distribution (Fig. S2).
3.5 Temperature programmed oxidation (TPO)
TPO analysis was performed on the used catalysts to measure carbon deposition.
For purpose of quantification comparison, carbon black was used as standard
substance. The spent catalyst A, B or reference material were carried out at the same
o
heating rate of 10 C·min-1. Fig. 4 showed that much lower amount of carbon was
deposited on catalyst A than that of B. Furthermore, several CO2 peaks were
observed, indicating different types of carbons with different reactivity toward
oxidation [39-40]. Besides, the peak maximum of carbon species in ferrite catalysts
was shifted to lower temperature compared with reference material, indicating that
the deposited carbon species were mainly oxidized by lattice or surface oxygen [41].
Thus, the TPO profile of spent catalysts suggesting catalyst A held good carbon
resistance than that of catalyst B.
3.6 Catalytic activity
It could be seen from Fig. 5 that conversion of CO increased with the rising of
temperature on these catalysts. The conversion of CO for catalyst B was the highest
during the whole reaction processing. Besides, the conversion of CO for catalyst A
o
was larger than that of catalyst C, except below 300 C. In other words, the catalyst A
showed better performance than commercial catalyst at higher temperature. At 360
oC, catalyst A, B and C showed the highest conversion of CO, which were 87.0 %, 94.6 %
and 39.9%, respectively.
o
Fig. 6 showed that the selectivity of CH4 for catalyst A was 70.1 % at 280 C,
furthermore it reached up to the maximum (72.8 %) when the temperature was 300
o
oC. However, the catalyst B and C exhibited the highest selectivity of CH4 at 320 C.
o
The selectivity of CH4 for catalyst C was larger than that of catalyst A above 300 C.
Catalyst B showed the lowest selectivity of CH4 on the whole. The different CO2
selectivity against temperature was shown in Fig.7. As a result, the ferrite catalyst
prepared from pure regents showed high CO2 selectivity, while the Ni-Al2O3 catalyst

showed much less CO2 selectivity. The predominent cause of the phenomenon was
that Ni catalysts were more favorable for the methanation than the WGS reaction
under high reaction pressure [42]. Surprisingly, the selectivity of CO2 for catalyst A
was as low as catalyst C. The low CO2 selectivity in catalyst A might be correlated with
the heavy metal modification which leaded to different reducibility and carburation
ability.
On the whole, catalyst A showed the higher CH4 selectivity, higher C2-4 selectivity
and lower CO2 selectivity than that of catalyst B and C. It could be elucidated that
catalyst A could be used to produce higher heating value SNG with appropriate
temperature.
To investigate the thermal stability of the catalysts, high temperature treatment
was performed and catalytic activity was tested before and after that. As shown in
Fig. 8 CO conversion of catalyst A decreased from 87.0 % to 57.6 % after heat
treatment, whereas that of catalyst B and C decreased from 94.6 % to 30.7 % and
39.9 % to 6.0 %, respectively. Both A and B exhibited higher catalytic reactivity after
high-temperature processing in contrast to catalyst C. The good resistance to thermal
shock of catalyst A and B might be due to spinel structure. Besides, the reason why
catalyst A showed the best resistance to thermal shock might be explained as the
heavy metal promotion, by which the spent catalyst A was dense, whereas catalyst B
occurred coagulations on the surface as shown in SEM (Fig. S3c-d). Such a privilege is
of great importance in the notorious strong exothermic reaction. A completely
engineering importance of it in methanation reaction was worth of further study.
푀퐽
푚표푙
푣표푙푢푚푒 푓푟푎푐푡ꢀ표푛∗ℎ푒푎푡 표푓 푐표푚푏푢푠푡ꢀ표푛(
)
푀퐽
4
∑
Heating value
(
)=
*
+
of
푁푚3
ꢀ=1
푁푚3
푠푝푒푐ꢀ푓ꢀ푐 푣표푙푢푚푒 (
)
푚표푙
hydrocarbon of carbon number (3)
The SNG calorie produced from catalyst A, B and C was calculated (according to
o
Eq. (3) and table 3), with the highest heating value of 41.7 (340 C) MJ·Nm-3, 32.3
o
o
(320 C) MJ·Nm-3 and 36.0 (320 C) MJ·Nm-3, respectively. The highest heating value
of catalyst A was ascribed to mediate CO2 content and C2+ hydrocarbons content.
Besides, catalyst C produced the least by-product comparing catalyst A and B. Thus,

the reason why catalyst A could produce high-calorie SNG and catalyst C always used
in methanation were obviously.
3.7 Stability
In order to investigate the stability of catalyst A, a long-term test was performed
o
under 340 C, 2 MPa up to 300 h. Fig. 9 showed the catalytic stability of catalyst A
during methanation process. In the 300 h stability test, the CO conversion, CH4 and
CO2 selectivity obtained on catalyst A maintained at about 65%, 50% and 13%,
respectively. No deactivation was observed in the time on stream, suggesting an
excellent catalytic stability of the catalyst prepared from electroplating sludge. Here,
the resistance to deactivation might be ascribed to the presence of heavy metals.
3.8 Economic assessment
The catalyst cost was evaluated for next step of application. Dealing
electroplating sludge would spend 149.81-299.63 $·t-1 nowadays. In other words,
producing catalyst A not only could ignore the cost of raw materials but also saved
the handling expense and offer environmental benefits. So, the feedstock of catalyst
A was assumed to be -224.72 $·t-1.
During hydrothermal processing, the electricity consumption was approximately
200 kw·h. The cost of desalted water was calculated at 2.55 $·t-1 and electricity was
0.12 $/kw·h.
Table 4 showed among the three catalysts, catalyst C was the most expensive
one which was almost 33 times than that of catalyst A. Catalyst B involved slightly
higher cost because of the use of pure chemicals regents, while catalyst A resulted in
most cost-saving because of the reuse of the electroplating sludge.
4. Conclusions
Ferrite catalysts were synthesized by facilitating waste material, i.e.,
electroplating sludge. Our study demonstrated that the sludge could be used as a
valuable resource for synthesizing a highly active and stable methanation catalyst.
Comparing with catalyst B prepared by pure reagents and catalyst C employed in
industry, electroplating sludge derived catalyst could produce higher heating value of
SNG, resist thermal shock perfectly and suppress water gas shift efficiently. Besides,

due to the presence of impurity elements catalyst A was more stable and kept intact
after reaction. In a word, a new promising route to handle electroplating sludge and
synthesis catalyst is provided by this work.
Acknowledgements
Financial support is acknowledged from the Natural Science Foundation of
China (Grant No. 21673272, 21373254) and PetroChina (Project No. 14-08-05-02).
We would like to thank Mr. Wenbin Zhang and Mr. Lei Xie for the facilitation in the
equipment maintenance, Mrs. Yingying Xue, Mr. Yongbiao Zhai, Mr. Yanting Liu and
Mr. Buhuan Wang for the helpful discussions.

Notes and references
[1] J. Zhang, J. Zhang, Y. Xu, H. Su, X. Li, J.Z. Zhou, G. Qian, L. Li, Z.P. Xu, Efficient
selective catalytic reduction of NO by novel carbon-doped metal catalysts made
from electroplating sludge, Environ. Sci. Technol. 48 (2014) 11497-11503.
[2] M. Arsenovic, Z. Radojevic, S. Stankovic, Removal of toxic metals from industrial
sludge by fixing in brick structure, Constr Build Mater 37 (2012) 7-14.
[3] N. Nagarajan, P. Gunasekaran, P. Rajendran, Genetic characterization, nickel
tolerance, biosorption, kinetics, and uptake mechanism of a bacterium isolated
from electroplating industrial effluent, Can. J. Microbiol. 61 (2015) 297-306.
[4] D. Chen, J. Hou, L.-h. Yao, H.-m. Jin, G.-R. Qian, Z.P. Xu, Ferrite materials prepared
from two industrial wastes: Electroplating sludge and spent pickle liquor, Sep.
Purif. Technol. 75 (2010) 210-217.
[5] V.R.R. Pendyala, G. Jacobs, M.K. Gnanamani, Y. Hu, A. MacLennan, B.H. Davis,
Selectivity control of Cu promoted iron-based Fischer-Tropsch catalyst by tuning
the oxidation state of Cu to mimic K, Appl. Catal. A: Gen. 495 (2015) 45-53.
[6] M. Al-Dossary, A.A. Ismail, J.L.G. Fierro, H. Bouzid, S.A. Al-Sayari, Effect of Mn
loading onto MnFeO nanocomposites for the CO2 hydrogenation reaction, Appl.
Catal. B: Environ. 165 (2015) 651-660.
[7] H. Wang, Y. Yang, J. Xu, H. Wang, M. Ding, Y. Li, Study of bimetallic interactions
and promoter effects of FeZn, FeMn and FeCr Fischer–Tropsch synthesis catalysts,
J. Mol. Catal. A: Chem. 326 (2010) 29-40.
[8] J. Gao, Q. Liu, F. Gu, B. Liu, Z. Zhong, F. Su, Recent advances in methanation
catalysts for the production of synthetic natural gas, RSC Adv. 5 (2015)
22759-22776.
[9] Y.H. Lee, D.-W. Lee, H. Kim, H.S. Choi, K.-Y. Lee, Fe–Zn catalysts for the production
of high-calorie synthetic natural gas, Fuel 159 (2015) 259-268.
[10]C. Cheng, D. Shen, R. Xiao, C. Wu, Methanation of syngas (H2/CO) over the
different Ni-based catalysts, Fuel 189 (2017) 419-427.
[11]C.G. Visconti, M. Martinelli, L. Falbo, A. Infantes-Molina, L. Lietti, P. Forzatti, G.

Iaquaniello, E. Palo, B. Picutti, F. Brignoli, CO2 hydrogenation to lower olefins on a
high surface area K-promoted bulk Fe-catalyst, Appl. Catal. B: Environ. 200 (2017)
530-542.
[12]Y. Li, Q. Zhang, R. Chai, G. Zhao, Y. Liu, Y. Lu, Structured Ni-CeO2-Al2O3/Ni-Foam
Catalyst with Enhanced Heat Transfer for Substitute Natural Gas Production by
Syngas Methanation, ChemCatChem 7 (2015) 1427-1431.
[13]T. Inui, A. Sakamoto, T. Takeguchi, Y. Ishigaki, Synthesis of Highly Calorific
Gaseous Fuel from Syngas on Cobalt-Manganese-Ruthenium Composite
Catalysts, Ind. Eng. Chem. Res. 28 (1989) 427-431.
[14]Y.H. Lee, H. Kim, H.S. Choi, D.-W. Lee, K.-Y. Lee, Co-Mn-Ru/Al2O3 catalyst for the
production of high-calorific synthetic natural gas, Korean J. Chem. Eng. 32 (2015)
2220-2226.
[15]H.M.T. Galvis, J.H. Bitter, C.B. Khare, M. Ruitenbeek, A.I. Dugulan, K.P.d. Jong,
Supported Iron Nanoparticles as Catalysts for Sustainable Production of Lower
Olefins, Science 335 (2012) 835-838.
[16]S.L. Soled, E. Iglesia, S. Miseo, B. DeRites, R. Fiato, Selective synthesis of α-olefins
on Fe-Zn Fischer-Tropsch catalysts, Top. Catal. (1995) 193-205.
[17]S. Li, A. Li, S. Krishnamoorthy, E. Iglesia, Effects of Zn, Cu, and K promoters on the
structure and on the reduction, carburization, and catalytic behavior of
iron-based Fischer–Tropsch synthesis catalysts, Catal. Lett. 77 (2001) 197-205.
[18]P. Liu, H. He, G. Wei, X. Liang, F. Qi, F. Tan, W. Tan, J. Zhu, R. Zhu, Effect of Mn
substitution on the promoted formaldehyde oxidation over spinel ferrite:
Catalyst characterization, performance and reaction mechanism, Appl. Catal., B
182 (2016) 476-484.
[19]Y. Wang, X. Wu, W. Zhang, W. Chen, Synthesis and electromagnetic properties of
La-doped Ni–Zn ferrites, J. Magn. Magn. Mater. 398 (2016) 90-95.
[20]K.E. deKrafft, C. Wang, W. Lin, Metal-Organic Framework Templated Synthesis of
Fe2O3/TiO2 Nanocomposite for Hydrogen Production, Adv. Mater. 24 (2012)
2014-2018.
[21]A.M. Afzal, M. Umair, G. Dastgeer, M. Rizwan, M.Z. Yaqoob, R. Rashid, H.S. Munir,

Effect of O-vacancies on magnetic properties of bismuth ferrite nanoparticles by
solution evaporation method, J. Magn. Magn. Mater. 399 (2016) 77-80.
[22]A. Hajalilou, S.A. Mazlan, K. Shameli, A comparative study of different
concentrations of pure Zn powder effects on synthesis, structure, magnetic and
microwave-absorbing properties in mechanically-alloyed Ni–Zn ferrite, J. Phys.
Chem. Solids 96-97 (2016) 49-59.
[23]A. Boudjemaa, I. Popescu, T. Juzsakova, M. Kebir, N. Helaili, K. Bachari, I.-C.
Marcu, M-substituted (M = Co, Ni and Cu) zinc ferrite photo-catalysts for
hydrogen production by water photo-reduction, Int. J. Hydrogen Energy 41 (2016)
11108-11118.
[24]N. Kavitha, P. Manohar, Magnetic and Electrical Properties of
Magnesium-Substituted Ni–Zn Ferrites, J Supercond Nov Magn 29 (2016)
2151-2157.
[25]W. Chen, Z. Fan, X. Pan, X. Bao, Effect of Confinement in Carbon Nanotubes on
the Activity, J. Am. Chem. Soc. 130 (2008) 9414-9419.
[26]C.-H. Zhang, H.-J. Wan, Y. Yang, H.-W. Xiang, Y.-W. Li, Study on the iron–silica
interaction of a co–precipitated Fe/SiO2 Fischer–Tropsch synthesis catalyst, Catal.
Commun. 7 (2006) 733-738.
[27]K. Jothimurugesan, J.G. Goodwin Jr, S.K. Gangwal, J.J. Spivey, Development of Fe
Fischer-Tropsch catalysts for slurry bubble column reactors, Catal. Today 58
(2000) 335–344.
[28]H. Suo, S. Wang, C. Zhang, J. Xu, B. Wu, Y. Yang, H. Xiang, Y.-W. Li, Chemical and
structural effects of silica in iron-based Fischer–Tropsch synthesis catalysts, J.
Catal. 286 (2012) 111-123.
[29]M. Qing, Y. Yang, B. Wu, J. Xu, C. Zhang, P. Gao, Y. Li, Modification of Fe–SiO2
interaction with zirconia for iron-based Fischer–Tropsch catalysts, J. Catal. 279
(2011) 111-122.
[30]R.P. Mogorosi, N. Fischer, M. Claeys, E. van Steen, Strong–metal–support
interaction by molecular design: Fe–silicate interactions in Fischer–Tropsch
catalysts, J. Catal. 289 (2012) 140-150.

[31]D.B. Bukur, X. Lang, D. Mukesh, W.H. Zimmerman, M.P. Rosynek, C. Li,
Binder/Support Effects on the Activity and Selectivity of Iron Catalysts in the
Fischer-Tropsch Synthesis, Ind. Eng. Chem. Res. 29 (1990) 1588-1599.
[32]H. Suo, C. Zhang, B. Wu, J. Xu, Y. Yang, H. Xiang, Y. Li, A comparative study of
Fe/SiO2 Fischer–Tropsch synthesis catalysts using tetraethoxysilane and acidic
silica sol as silica sources, Catal. Today 183 (2012) 88-95.
[33]S. Li, A. Li, S. Krishnamoorthy, E. Iglesia, Effects of Zn, Cu, and K promoters on the
structure and on the reduction, carburization, and catalytic behavior of
iron-based Fischer-Tropsch synthesis catalysts, Catal. Lett. 77 (2001) 197-205.
[34]C. Zhang, Y. Yang, B. Teng, T. Li, H. Zheng, H. Xiang, Y. Li, Study of an
iron-manganese Fischer–Tropsch synthesis catalyst promoted with copper, J.
Catal. 237 (2006) 405-415.
[35]R. Benrabaa, A. Löfberg, J. Guerrero Caballero, E. Bordes-Richard, A. Rubbens,
R.-N. Vannier, H. Boukhlouf, A. Barama, Sol–gel synthesis and characterization of
silica supported nickel ferrite catalysts for dry reforming of methane, Catal.
Commun. 58 (2015) 127-131.
[36]Y.-H. Huang, S.-F. Wang, A.-P. Tsai, S. Kameoka, Reduction behaviors and catalytic
properties for methanol steam reforming of Cu-based spinel compounds CuX2O4
(X=Fe, Mn, Al, La), Ceram. Int. 40 (2014) 4541-4551.
[37]A. Zarei Senseni, S.M. Seyed Fattahi, M. Rezaei, F. Meshkani, A comparative study
of experimental investigation and response surface optimization of steam
reforming of glycerol over nickel nano-catalysts, Int. J. Hydrogen Energy. 41 (2016)
10178-10192.
[38]J. Zhang, J.-M. Song, H.-L. Niu, C.-J. Mao, S.-Y. Zhang, Y.-H. Shen, ZnFe2O4
nanoparticles: Synthesis, characterization, and enhanced gas sensing property
for acetone, Sensors Actuators B: Chem. 221 (2015) 55-62.
[39]L. Dong, C. Wu, H. Ling, J. Shi, P.T. Williams, J. Huang, Promoting hydrogen
production and minimizing catalyst deactivation from the pyrolysis-catalytic
steam reforming of biomass on nanosized NiZnAlOx catalysts, Fuel 188 (2017)
610-620.

[40]A. Vita, C. Italiano, C. Fabiano, L. Pino, M. Laganà, V. Recupero, Hydrogen-rich gas
production by steam reforming of n-dodecane, Appl. Catal. B: Environ. 199 (2016)
350-360.
[41]S.A. Theofanidis, R. Batchu, V.V. Galvita, H. Poelman, G.B. Marin, Carbon
gasification from Fe-Ni catalysts after methane dry reforming, Appl. Catal. B:
Environ. 185 (2016) 42-55.
[42]D. Tian, Z. Liu, D. Li, H. Shi, W. Pan, Y. Cheng, Bimetallic Ni–Fe total-methanation
catalyst for the production of substitute natural gas under high pressure, Fuel
104 (2013) 224-229.

Fig. 1. The treatment process of electroplating wastewater to sludge
(PMA: Polyscrylamide)

Fig. 2. XRD patterns of samples: Catalyst A, the ferrite sample prepared by sludge;
Catalyst B, the ferrite sample prepared from chemical regents; Spent Catalyst A, the
spent ferrite sample prepared by sludge; Spent Catalyst B, the spent ferrite sample
prepared from chemical regents.

Fig. 3. H2-TPR curves of samples: Catalyst A, the ferrite sample prepared by sludge;
Catalyst B, the ferrite sample prepared from chemical regents; Catalyst C, sample
J101 purchased from Nanjing Chemical Catalyst factory.

Fig. 4. O2-TPO profile: CO2 intensity as a function of temperature for used ferrite
sample prepared by sludge (Catalyst A), used ferrite sample prepared from chemical
regents (Catalyst B) and carbon black (Reference material). Heating rate of 10
oC·min-1.

Fig. 5. The conversion of CO with the rising of temperature during methanation
reaction. Reaction conditions: 2.0MPa, H2/CO = 2. Catalyst A: the ferrite sample
prepared from sludge; Catalyst B: the ferrite sample prepared from chemical regents;
Catalyst C: sample J101 purchased from Nanjing Chemical Catalyst factory.

Fig. 6. The selectivity of CH4 with the rising of temperature during methanation
reaction. Reaction conditions: 2.0MPa, H2/CO = 2. Catalyst A: the ferrite sample
prepared from sludge; Catalyst B: the ferrite sample prepared from chemical regents;
Catalyst C: sample J101 purchased from Nanjing Chemical Catalyst factory.

Fig. 7. The selectivity of CO2 with the rising of temperature during methanation
reaction. Reaction conditions: 2.0MPa, H2/CO = 2. Catalyst A: the ferrite sample
prepared from sludge; Catalyst B: the ferrite sample prepared from chemical regents;
Catalyst C: sample J101 purchased from Nanjing Chemical Catalyst factory.

Fig. 8. The conversion of CO before and after the high-temperature processing:
Catalyst A, the ferrite sample prepared from sludge; Catalyst B, the ferrite sample
prepared from chemical regents; Catalyst C, sample J101 purchased from Nanjing
Chemical Catalyst factory. Reaction conditions: 360 oC, 2.0MPa, H2/CO = 2

Fig. 9. Stability test of Catalyst A : ferrite sample prepared from sludge. Reaction
conditions: 340 oC, 2.0MPa, H2/CO = 2.