Paper
Catalysis Science & Technology
2. Materials and methods
2.1. Preparation and characterization of SWs
measure the conversion of m-cresol and TOC removal. At the
end of each experiment, the reactor was cooled down to room
temperature and opened to recover the remaining SW cata-
lyst. The catalyst was separated by filtration, whilst the
remaining solution was stored for further analysis of the pH,
m-cresol, TOC and metal ions leached from the catalyst.
The catalytic activity and stability of the SW catalysts in
CWAO were tested in a fixed-bed reactor with upflow of
m-cresol wastewater and air. The exact characteristics of the
reactor and the catalyst bed are presented in Fig. S1 and S2.†
The size of the catalytic particles was less than 2 mm. The
gas and liquid flow rates were 40 mL min−1 and 0.17 mL
min−1, respectively. The operating temperature and reaction
pressures ranged from 180 °C to 220 °C and 20 to 33 bar,
respectively.
SWs were prepared by using municipal sewage sludge from a
wastewater treatment plant (WWTP) in Dalian (China). Sew-
age sludge was dried to constant weight at 105 °C and car-
bonized at 600 °C for 4 h under a heating rate of 3 °C min−1
and a high purity nitrogen (99.999 wt%) flow of 500 mL
min−1. After the furnace had cooled to room temperature,
SWs were obtained. In order to modify the surface of SWs,
different acids were used to treat the SWs. In the acid treat-
ment process, 50 mL of SWs were produced by immersing
carbonized SWs with the same volume of HCl (20.5 wt%),
H2SO4 (63.4 wt%) and HNO3 (40.5 wt%) for 24 h, respectively.
Then, HCl-SW, H2SO4-SW and HNO3-SW were washed with
deionized water until the pH of the washing water reached 6–
7 and the recovered solids were dried at room temperature.
X-ray Fluorescence (XRF) was used to analyze the element
content in the SW samples with Magix 601 equipment pro-
duced by PANalytical. Thermogravimetric analysis (TGA)
(WRT-1D, China) was performed to measure the amount of
carbon in SWs. The X-ray diffraction (XRD) spectra were
obtained by using an X'Pert PRO instrument produced by
PANalytical with Cu Kα (λ = 1.5406 Å) radiation at 40 kV and
40 mA in the 2θ scan range of 10–90°. The functional groups
on the SWs were analyzed by Fourier Transform Infrared
Spectroscopy (FTIR, Tensor 27, Germany). X-ray photoelec-
tron spectroscopy (XPS) was performed to analyze the compo-
sition and chemical state of the surface elements of the SW
catalysts. A Thermo ESCALAB250Xi instrument, with an Al K
X-ray source (1486.6 eV) and a pass energy of 20 eV, was used
at a pressure of 6.5 × 10−5 Pa. The binding energies were cali-
brated with respect to the signal for contamination carbon
2.3. Analysis methods
All solutions used in this study were prepared in deionized
water of 18.25 MΩ cm−1. m-Cresol, nitric acid, sulfuric acid
and hydrochloric acid were of analytical grade.
The concentration of m-cresol was analyzed via High-
Performance Liquid Chromatography (HPLC). The HPLC sys-
tem (Dalian Elite Analytic Instruments Co., Ltd) was
equipped with an Elite C18 chromatographic column (4.6
mm × 250 mm, 5 μm) and a UV-detector set at 272 nm. The
mobile phase was methanol : water = 80 : 20 (V/V) and the flow
rate was fixed at 1.0 mL min−1.
A total organic carbon (TOC) analyzer (TOC-VCPH/CPN
,
Shimadzu, Japan) was employed to determine the residual
amounts of organic substances in the effluent.
The pH of the m-cresol solution was measured using a
REX PHS-3C pH meter (Rex Instrument Factory, Shanghai,
China), and the meter was calibrated daily before use.
High-performance liquid chromatography-mass spectrom-
etry (HPLC-MS) was used to investigate the intermediates in
treated solutions by using an Agilent Q-TOF 6540 mass
spectrometer.
(binding energy
= 284.6 eV). Temperature-programmed
desorption (TPD) was used to measure the surface functional
groups on the SW catalysts. The SW powder sample was
treated at room temperature for 2 h under pure He (99.999%)
flow. Then sample was heated up to 900 °C with a heating
rate of 6 °C min−1 under pure He (99.999%) flow. The
desorbed CO and CO2 were detected with a mass spectrome-
ter (Pfeiffer Vacuum, Ominstar GSD 301 O2).
Gas chromatography-mass spectrometry (GC-MS) was uti-
lized to identify the intermediates in treated solutions. In
order to detect the intermediate of low molecular weight
acids from m-cresol degradation in CWAO, an esterification
reaction was used to prepare the sample. The esterification
method was given as follows. First of all, a liquid sample was
concentrated through a rotary evaporator. Secondly, 2 mL of
10% (v/v) H2SO4 in alcohol was mixed with the residuals in a
vial and placed in an oven at 60 °C for 8 h. While the mixture
was cooled, it was neutralized with 1 mL of saturated Na2CO3.
Then, 1 mL of hexane was added into the mixture to extract
the fatty acids by stirring for 2 min. When the mixture set-
tled, a pipette was used to remove the top hexane layer and
transfer it into another vial. Finally, the dried hexane layer
dried with Na2SO4 (anhydrous) to remove any residual water
was filtered for GC-MS analyses. An Agilent model 7890A Gas
Chromatograph (GC) equipped with a model 5975C mass
selective detector and a capillary column (HP-5ms, 30 m ×
2.2. Degradation experiments
The catalytic activity of the prepared SWs was assessed in a
500 mL batch reactor equipped with a magnetic stirrer and
an electric heating jacket. The reactor was a CJF-0.5-type
autoclave made of titanium alloy supplied by Dalian Tongda
Autoclaves Plant. In a standard experiment, 200 mL of
m-cresol (5000 mg L−1) solution and 1 g of the catalyst were
put into the autoclave. The size of the catalytic particles was
less than 60 mesh. The reactor was closed and filled with a
certain pressure of oxygen (6.6 bar), then the heating-up pro-
gram was started. When the set temperature was attained,
the stirring started at a speed of 600 rpm. This time was
taken as the zero time and the liquid specimens were taken
after 15 min, 30 min, 45 min, 60 min, 75 min and 90 min to
Catal. Sci. Technol.
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