RSC Advances
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Au3+ was absorbed on the mesopores of the AC shows that this performed using the ASAP 2920, using 10% CO2 (or NH3) in
is the main site of activity while the micropores can be ignored argon (ow 50 ml minꢀ1, holding for 30 min) as the adsorption
in order to improve the usage of Au.12 Meanwhile, the discon- gas and a temperature ramp from 50 to 700 ꢁC (ramp rate, 10 ꢁC
tinuous distribution and disposable activity were its major minꢀ1) when adsorbing. The morphology of the samples was
shortcomings. All the above facts prompted us to consider examined using scanning electron microscopy (SEM) with a
whether gamma-aluminium oxide (g-Al2O3), which has a mes- Nova NanoSEM 450 (FEI, The Netherlands). X-ray diffraction
oporous (20–50 nm) structure and contains abundant hydroxyl (XRD) data were collected using a D8 advanced X-ray diffrac-
groups on the surface, could be an efficient support for Au- tometer (Bruker) with Cu-Ka irradiation at 40 kV and 40 mA in
based catalysts in acetylene hydrochlorination. Recently, g- the scanning range from 10ꢁ to 80ꢁ. Hydrogen temperature-
Al2O3 was used as the support for preparing Au-based catalysts programmed desorption (H2-TPR) was performed using the
for carbon monoxide oxidation14,15 and hydrodechlorination of ASAP 2920, using 10% H2 in argon (ow 50 ml minꢀ1) as the
carbon tetrachloride.16 However, as far as we are concerned, reductive gas and a temperature ramp of 50 to 600 ꢁC (ramp
there is very little literature11,12 reporting Au-based catalysts rate, 10 ꢁC minꢀ1) with a thermal conductivity detector
supported on g-Al2O3, and there is still much room for recording the signal. Fourier-transform infrared (FT-IR) spectra
improvement.
were obtained using a 6700 FT-IR spectrometer (Thermo Fisher
In this work, the g-Al2O3 was employed as the support for the Nicolet). XPS data were collected using an Axis Ultra spec-
gold(III) chloride–copper(II) chloride (AuCl3–CuCl2) catalyst for trometer (Kratos Analytical) with a monochromatized Al-Ka
acetylene hydrochlorination. Because of its mesoporous struc- X-ray source and a minimum energy resolution of 0.48 eV
ture, AuCl3–CuCl2 supported on g-Al2O3 can effectively reduce (Ag 3d5/2).
the content of the Au component. It was found that some g-
Al2O3 have some special characteristics, and that they can be
efficient supports for the catalyst. The possible mechanisms
accounting for the enhanced stability and catalytic efficiency are
also discussed. The effects of textural properties and acid/base
site of the g-Al2O3 support on the catalyst activity were also
studied in detail. In addition, the reasons for deactivation and
the regeneration method were also investigated.
2.3 Catalyst testing
The catalytic performance for acetylene hydrochlorination was
evaluated in a xed-bed microreactor (diameter 10 mm) oper-
ating at a pressure of 0.1 MPa and a temperature of 150 ꢁC. The
reactor was purged with N2 to remove water in the reaction
system before the reaction occurred. Hydrogen chloride passed
through the reactor at a ow rate of 50 ml minꢀ1 for 2 h to
activate the catalyst. Aer the reactor was heated to 150 ꢁC,
acetylene (20 ml minꢀ1) and hydrogen chloride (22 ml minꢀ1
)
2. Experimental section
2.1 Catalyst preparation
were fed through the heated reactor, which contained 10 ml of
catalyst. The reaction product was analyzed by gas chromatog-
raphy (GC-920, Al2O3 PLOT column). The catalyst activity was
determined by the conversion of acetylene (XC H ) and selectivity
Bimetallic Au–Cu/g-Al2O3 catalysts were prepared using an
incipient wetness impregnation technique.8 g-Al2O3 (A, B, C, D)
from different companies (10 g, Hengxin, Yuanheng, Hong Xing
and BaoLai Co. Ltd, China) were initially washed with dilute
2
2
of VCM (SVCM), which are dened as:
aqueous hydrochloric acid (HCl; 1 mol lꢀ1) at 25 C for 1 h to
XC H ¼ (1 ꢀ FC H ) ꢂ 100%
(1)
(2)
ꢁ
2
2
2
2
remove the impurities on the surface. Then the catalyst was
prepared by impregnating the g-Al2O3 with 2 ml of HAuCl4$4H2O
(Au content assay 49.7%) aqua regia solution (1 g HAuCl4$4H2O/
100 ml) and 20 ml of CuCl2$2H2O solution (6.25 g CuCl2$2H2O/
500 ml), stirred for 3 h at 353 K, then dried at 423 K for 12 h. The
catalysts prepared by different supports were donated as ACAlA,
ACAlB, ACAlC, ACAlD. Some of the catalysts were named MAC-
AlB, namely B pretreated with potassium hydroxide (KOH)
denoted as MB, and the catalysts were prepared based on the
process described elsewhere,8 in order to distinguish the effect of
basic sites.
SVCM ¼ FVCM/(1 ꢀ FC H ) ꢂ 100%
2
2
Of which FC H is the residual volume fraction of acetylene
2
2
and FVCM is the volume fraction of chloroethylene.
3. Results and discussion
3.1 Catalytic activity
Catalysts with different supports were used in a xed bed
reactor to assess their catalytic performance for acetylene
hydrochlorination. The XC H and SVCM with reaction time are
2
2
illustrated in Fig. 1. It shows that all the catalysts had excellent
selectivity toward vinyl chloride (C2H3Cl) (Fig. 1a). However,
2.2 Catalyst characterization
Brunauer, Emmett and Teller (BET) surface area analysis and their activities were quite different (Fig. 1b). The catalysts'
pore size distribution were performed by obtaining nitrogen activity initially exhibited a growing trend, but then decreased
(N2) adsorption isotherms at 77 K using a ASAP2020 accelerated aer running for 2 h. ACAlD had the best performance among
surface area and porosimetry analyzer (Micromeritics). the samples with the highest conversion of 96% and stabiliza-
Temperature programmed analysis including carbon dioxide tion of about 90%. For comparison, the three other catalysts
temperature-programmed desorption (CO2-TPD) and ammonia had conversions from 40% to 80%, which were signicantly
temperature-programmed
desorption
(NH3-TPD)
was lower.
16728 | RSC Adv., 2015, 5, 16727–16734
This journal is © The Royal Society of Chemistry 2015