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analysis (SEM-EDX), power X-ray diffraction analy- Gauss–Lorentz curves to determine binding energies
sis (XRD), X-ray photoelectron spectroscopy (XPS), of different elements. Infrared spectra were recorded
electron spin resonance (ESR), transmission electron in KBr pellets using thermo Nicolet Nexus 670 spec-
microscopy (TEM) and Fourier transformed infrared trometer in the region of 4000-400 cm−1. The spec-
(FT-IR) spectroscopy.
trum obtained after multiple scans was a plot of
percentage transmittance against wave number. ESR
analysis of Zn-Cr-O samples were performed at room
temperature using JEOL/JES-FA200 spectrophotome-
ter by X-band equipment with an operating frequency
υ = 9.029 GHz. DT/TGA of the oven-dried samples
were recorded using a Leeds and Northup (USA) unit at
a heating rate of 10◦C/min, ranging from 30◦ to 1000◦C
under nitrogen flow.
2. Experimental
2.1 Preparation of catalysts
The Zn–Cr catalysts employed in this investigation
were prepared by a simple co-precipitation method
using Zn(NO3)2·6H2O and Cr(NO3)3·9H2O (Sigma–
Aldrich, AR grade) with Zn:Cr = 2:1 (mole ratio), in
prepared at two different pH, i.e., at pH 7 and 9 using
a mixture of 2M NaOH+1M Na2CO3 (base mixture)
as precipitating agent. Gels were washed thoroughly,
filtered and oven-dried for 12 h at 120◦C, and subse-
quently, calcined in static air at 450◦C for 5 h. The
Zn-Cr samples prepared at pH ∼ 7 and ∼ 9 were
denoted as ZC7 and ZC9, respectively. The bulk Cr2O3
catalyst was prepared by precipitation method using
Cr(NO3)3·9H2O (Sigma–Aldrich, AR grade) with simi-
lar composition of base mixture used here. All these
samples were screened for dehydrocyclization of EDA
and aqueous glycerol and some of the samples were
characterized by various spectroscopic techniques.
2.3 Activity measurements
Catalytic activities were carried out using –18/+23
sieved (BSS) catalyst particles. Carbon mass balance
was done based on the inlet and outlet concentra-
tion of the organic moiety. Prior to the reaction, about
0.2 g of calcined catalyst (sieved particles –18/+23
BSS) was reduced in 5% H2 (balance Ar) at 400◦C
for 5 h. Catalytic activities were measured under strict
kinetic control. An aqueous glycerol solution (20 wt%
in H2O) was used with a glycerol to EDA mole
ratio of 1:1, and a flow rate of the reaction mix-
ture of 5 mL h−1, with N2 as the carrier gas at a
flow rate of 1800 cc h−1. The reaction mixture con-
tained a glycerol:EDA:H2O:N2 = 1:1:20.4:7.4 mole
ratio.
2.2 Characterization of catalysts
2.4 Product analysis
Surface properties of the Zn-Cr-O samples were mea-
sured by N2 adsorption at –196◦C in an Autosorb Samples were analysed by gas chromatograph
3000 physical adsorption apparatus. Specific surface (Shimadzu, GC-17A) via a flame ionization detector
areas were calculated applying BET method. Calcined (FID) using a ZB-5 capillary column at a ramping
forms of Zn–Cr-O catalysts were characterized by rate of 10◦C min−1 from 60◦ to 280◦C. Mass balance
powder XRD analysis using a Rigaku Miniflex X-ray for all the measurements was >95%. Samples were
diffractometer using Ni-filtered Cu Kα radiation (λ = analysed by GC-MS (QP5050A Shimadzu) using a
0.15406 nm) from 2θ = 20 to 80◦, at a scan rate of ZB-5 capillary column with EI mode. Mass spectra
2◦ min−1 with beam voltage and beam current of 30 kV confirmed product distribution and corresponding m/z
and 15 mA, respectively. SEM-EDX analysis was car- values for methylpyrazine: M+. m/z: 94, (M-HCN)
ried out using JEOL-JSM 5600 instrument. For TEM +. m/z: 67, (M-CH3CN) +. m/z: 53, (M-C3H4N) +.
analysis, samples were dispersed in methanol solution m/z: 40; pyrazine: M+. m/z: 80, (M-HCN) +. m/z:
and suspended on a 400-mesh; 3.5 mm diameter Cu grid 53; EDA: (M-H)+ m/z: 59, (M-NH3)+. m/z: 43; glyc-
and images were taken using JEOL JEM 2010 high- erol: (M-CH2OH)+. m/z: 61; {M-(CH2OH, H2O)}+.
resolution transmission electron microscope. XPS pat- m/z: 43; 2,5-dimethylpyrazine: M+. m/z: 108; (M-
terns were recorded using a Kratos Axis Ultra Imaging CH3)+. m/z: 93; (M-HCN) +. m/z: 81; (M-CH3CN) +.
X-ray photoelectron spectrometer equipped with Mg m/z: 67; (M-C3H6N)+. m/z: 52; (M-C4H4N) +. m/z:
anode and a multichannel detector. Charge referencing 42; pyrazinealdehyde: M+. m/z: 108; (M-H)+. m/z:
was done against adventitious carbon (C 1s, 284.8 eV). 107; (M-CO)+. m/z: 80; (M-C2N2)+. m/z: 56; {M-
Shirley-type background was subtracted from the (H,CO,C2H2)}+. m/z: 53; and 2,3-dimethylpyrazine:
signals. Recorded spectra were always fitted using M+. m/z: 108; (M-CH3CN)+. m/z: 67; (M-C4H6N)+.