Chemical Papers
equipped with energy-dispersive spectroscopy (EDS), which
was used to investigate the elementary composition of the
particles.
of saturated sodium bicarbonate solution, transferred to a
separatory funnel and extracted with CHCl (2 × 10 mL).
3
The organic layers were combined, dried with anhydrous
The number of acid sites of the prepared sample and the
precursor materials was determined by the titration method,
follow the process in (Ventura et al. 2017). In the experi-
ments, 20 mL of a sodium hydroxide aqueous solution
Na SO , ꢂltered and transfer to a volumetric ꢃask (25 mL)
2
4
with CHCl . Quantiꢂcation was performed on Gas Chroma-
3
tograph (Shimadzu, GC-2010 Plus Tracera) equipped with
SH-Rtx-5 capillary column and barrier discharge ioniza-
tion (BID) detector. Aniline conversion and product ratios
were determined by external calibration curves obtained by
known concentrations of authentic samples. The obtained
products were also confirmed by GC–MS (Shimadzu,
GCMS-QP2010).
−
1
of known concentration (0.01 mol L ) was added to the
powder (using a mass of 10 mg). The mixture was stirred
during 24 h at room temperature. Upon separation by cen-
trifugation, the supernatant solution was then titrated with
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1
hydrochloric acid (0.05 mol L ) aqueous solution using
phenolphthalein as an indicator. Posteriorly, acid sites quan-
tity within the catalysts was determined by the following
equation:
Conversion of aniline was calculated by:
moles of reactant reacted
Conversion (% ) =
× 100,
initial moles of reactant used
(
3)
NAS = (NNaOH −NHCl) × L,
(2)
whereas selectivity of products using the following
expression:
where NAS=number of acid sites, NNaOH=initial quantity
of NaOH added (moles), NHCl=quantity of HCl consumed
(
moles) and L is the Avogadro constant. The relative acid
Selectivity (%)
strength of the samples was determined by temperature-
programmed desorption of pyridine (TPD-Py) experiments.
Prior to TPD, the samples were heat treated under He ꢃow
total moles of product formed
=
× 100.
the sum of total moles of all oxidation products formed
(4)
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1
(
20 mL min ) at 700 °C for 30 min and cooled under the
Results and discussion
same gas ꢃow to 40 °C. Pyridine adsorption was carried out
using a ꢃow of He containing pyridine vapor (20 mmHg)
through the reactor for 30 min at 40 °C. After baseline stabi-
The inꢃuence of milling time on mean particle size was
monitored (Table 1) and sizes of 10, 50 and 90% of the
particles (D10, D50, and D90, respectively) were obtained.
After 120 min, the main particles sizes were not aꢁected and
remained stable at around 14 μm.
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1
lization under He ꢃow (20 mL min ) at room temperature,
the Py-TPD run was carried out with a heating rate of 10 °C
−
1
min from room temperature up to 750 °C. The pyridine
desorption was monitored using a thermal conductivity
detector (TCD).
Figure 1a shows the X-ray spectrum of the powder sam-
ple after milling and calcination process. The peaks are
intense and sharp, which can be correlated with its crystal-
linity. The higher peak counts are indexed according to the
JCPDS card no. 41-0347 associated with Al O . The peaks
N2-adsorption/desorption isotherms were obtained at liq-
uid nitrogen temperature (− 196 °C). Before the analysis, the
degassing was carried out at 200 °C for 2 h under vacuum.
The Brunauer–Emmett–Teller (BET) equation was applied
to the results to calculate surface area.
2
3
in smaller amounts are indexed according to the JCPDS card
no. 46-1212 associated with AlNbO . It may conꢂrm the
4
The H temperature programmed reduction (H -TPR)
2
2
ꢂnal product mixture which has Al O and AlNbO with
2
3
4
measurement was carried out in a quartz reactor heating
~
72% and~28%, respectively. The mean crystallite size is
from 45 to 990 °C using an 8% H /N gas mixture ꢃow
2
2
−
1
−1
(
20 mL min ) at a heating rate of 10 °C min . Before
the H -TPR tests, the sample (300 mg) was heat-treating at
2
Table 1 Particle size distribution as a function of high-energy milling
2
00 °C under N ꢃow for 0.5 h. The H consumption was
2 2
time
monitored by a thermal conductivity detector (TCD).
The liquid phase oxidation of aniline was performed
according Ventura et al. (2017) and Carreno et al. (2018).
In a one-necked round bottom ꢃask (10 mL) equipped with
a stir bar, the following were added: 10 mg of catalyst,
Time (min)
Mean diam- D10 (μm)
eter (μm)
D50 (μm)
D90 (μm)
0
19.68
17.95
14.53
14.42
13.59
13.74
14.33
1.36
1.14
1.06
1.01
0.91
0.99
0.96
17.07
14.61
12.24
11.64
10.57
11.35
10.84
43.1
40.6
31.9
32.5
31.5
30.6
34.2
3
6
9
1
1
1
0
0
3
mL of the speciꢂc organic solvent, 0.10 mL of aniline and
0
ꢂnally 0.15–1.0 mL of H O (35% aq. solution). The reac-
2
2
20
50
80
tion was maintained at 25 °C using a hotplate stirrer with
oil bath for times varying from 3 to 48 h. Once the reaction
was completed, it was quenched by the addition of 10 mL
1
3