peaks of the first peak shifted to lower temperatures regions, the possible reason is that, on one hand, BiOCl active
component with higher dispersion and smaller particle size were easily reduced; on the other hand, sulfur addition
can adsorption of the surface of the BiOCl nanoparticles and make it easier to be reduced. As a result, BiS0.5/AC
possesses a relative higher catalytic activity.
<InlineImage2> <InlineImage3> <InlineImage4> <InlineImage5>
X-ray photoelectron spectroscopy (XPS) was used to determine the electronic property of surface chemical
compositions of the fresh and used catalysts. Fig. 3 displays the Bi 4f regions of XPS spectra of the Bi/AC and
BiS0.5/AC catalysts. To detect any shift more precisely, the positions of Bi 4f peaks were referred to the main peak
of C 1s (284.6 eV). Comparison between the spectra of two fresh catalysts Bi/AC and BiS0.5/AC (Table S1 in
Supporting information) indicated that the binding energy for the Bi 4f peak of fresh BiS0.5/AC is shifted negatively
ca. 0.5 eV relative to the energy observed for the freshly Bi/AC catalyst. This negative shift in the Bi 4f binding
energy of BiS0.5/AC catalyst is due to the decreasing in the size of the active component and the attachment of the
sulfur species onto the BiOCl surface [21]. Therefore, the active site increasing in the BiS0.5/AC catalyst leads to the
promotion in the catalytic performance. Besides, the positive shift of Bi 4f binding energy for the used catalysts
reveals the growth of the BiOCl during the running time, resulting in the decreasing of the catalytic performance
for acetylene hydrochlorination reaction. In Fig. S4 (Supporting information), the binding energy of the sulfur
species was found to be 168.7 eV, demonstrating the presence of SO42 in the catalyst [22,23].
<InlineImage6>
To explore the reason for the enhanced catalytic performance of S-promoted Bi/AC catalyst, low-temperature N2
adsorption/desorption experiments were performed to investigate the textural properties of the Bi-based catalysts
with the addition of H2SO4. Table 1 listed the specific surface area, pore volume of the fresh and used Bi/AC and
BiSX/AC catalysts. Compared with Bi/AC, these BiS0.1/AC, BiS0.5/AC and BiS1/AC catalyst have a larger Brunauer-
Emmett-Teller (BET) surface area and this value decreased with the enhancement of H2SO4 doping. The rising of
the specific surface area is probably due to the hindered crystal growth of bismuth oxychloride by sulfur doping,
consistent with the XRD and H2-TPR results. In addition, the specific surface area and total pore volume of the
spent catalysts are lower than those of fresh catalysts, indicating the coke deposition formation or BiOCl particle
sintering occurred during the reaction time, which usually caused the deactivation of catalyst [7,24].
Thermogravimetric analysis (TGA) was performed to provide direct evidence to the coke deposition formation,
which usually caused deactivation of catalysts [25,26]. Experiment was operated under an air atmosphere and the
results are illustrated in Fig. S5 (Supporting information). The quantity of carbon deposits should identical to the
difference in mass loss between the fresh and used catalysts within the temperature range of coke burning. The
weight losses of fresh and spent Bi/AC catalysts in the range of 150-350 °C are 3.8% and 4.8%, respectively, which
suggested that the actual amount of coke deposition is 1%. The actual quantity of coke deposition by the BiS0.5/AC
is 1.6%, which is higher than that deposited on the Bi/AC catalyst. Therefore, the coke deposited on the BiS0.5/AC
catalyst occurs to a greater extent than that by the Bi/AC catalyst, consistent with the XRD results. Thus, the
enhanced stability of BiS0.5/AC catalyst cannot be attributed to the coke effect of the catalyst [27].
Overall, BiSX/C catalysts with different Bi/S molar ratios were synthesized and BiS0.5/C exhibited better catalytic
performance than Bi/C catalyst for the acetylene hydrochlorination reaction. The enhanced catalytic performance
was mainly attributed to the better dispersion of the BiOCl particles and elevating of the specific surface area of
the catalysts, which consequently led the BiS0.5/AC catalyst with increased amount of accessible active sites.
Therefore, the introduction of promoter was demonstrated as an effective method to improve the catalytic
performance of the nonmercuric non-noble catalysts for acetylene hydrochlorination reaction.
Acknowledgment
This work was supported by the National Natural Science Foundation of China (Nos. U1403293, 21263025) and the Graduate Research
and Innovation Program of Xinjiang (No. XJGRI2015010).
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