A series of SiO2-supported fourth period transition metal catalysts (M/SiO2) was prepared by a wetness impregnation method for the dehydrochlorination of 1, 1, 2-trichloroethane (TCE) in the gas phase. Among these M/SiO2 catalysts, Zn/SiO2 had the best catalytic activity with the highest TCE conversion (~98%) and excellent selectivity for cis-1, 2-dichloroethylene (82%). By increasing the zinc loading, the conversion of TCE using the Zn/SiO2 catalyst was gradually improved, in agreement with the total acidity in the Zn/SiO2 catalyst. Associating the specific activity and specific acidity of the Zn/SiO2 catalyst with different Zn loadings, it was found that higher specific acidity contributed to higher specific activity, indicating that the acid center of Zn/SiO2 was the catalytic active site for the dehydrochlorination of TCE. In the process of dehydrochlorination, the Zn/SiO2 catalyst could be deactivated, mainly due to coke deposition on the catalyst surface. Catalysts with low Zn loading had stronger acid sites, which resulted in more coke formation on the catalyst. The results showed that strong acid sites on the catalyst surface were responsible for the deposition of coke and deactivation of the catalyst.
Received: 25 November 2016
Published: 08 February 2017
Fig 1 Dehydrochlorination of 1, 1, 2-trichloroethane (TCE) catalyzed by SiO2-supported transition metals (a) TCE conversion; (b) selectivity to cis-1, 2-dichloroethylene (cis-DCE); (c) selectivity to trans-1, 2-dichloroethylene (trans-DCE); reaction condition: amount of catalyst, 0.30 g; pretreatment condition: 500 ℃ in N2 for 1.5 h; reaction temperature: 350 ℃; space velocity: 1000 h-1
Fig 2 Effect of Zn precursor (Zn (NO3)2 orZnCl2) on the dehydrochlorination of 1, 1, 2-trichloroethane (TCE) over 10% Zn/SiO2 (a) Zn (NO3)2; (b) ZnCl2. reaction condition: amount of catalyst, 0.30 g; pretreatment condition, 500 ℃ in N2 for 1.5 h; reaction temperature, 350 ℃; space velocity: 1000 h-1
Table 1Effect of pretreatment temperature, reaction temperature and space velocity on the dehydrochlorination of TCE over 10% Zn/SiO2 a
Fig 3 Effect of Zn loadings on the dehydrochlorination of TCE over Zn/SiO2 catalysts (a) TCE conversion; (b) selectivity to cis-DCE. reaction condition: amount of catalyst, 0.30 g; pretreatment condition: 500℃ in N2 for 1.5 h; reaction temperature, 350 ℃; space velocity: 1000 h-1
Fig 4 Dehydrochlorination of TCE over Zn/SiO2 catalysts after decreasing the amount of Zn catalysts (a) TCE conversion; (b) specific activity; (c) selectivity to cis-DCE. reaction condition: amount of catalyst, 0.10 g; pretreatment condition, 500 ℃ in N2 for 1.5 h; reaction temperature: 350 ℃; space velocity: 1000 h-1
Fig 5 XRD and BET characterization of SiO2 and 10% Zn/SiO2 catalysts
Fig 6 SEM (a, b) andTEM (c, d) characterization for fresh and used 10% Zn/SiO2 catalysts
Fig 7 High-resolution XPS data of the Zn 2p3/2 peak for the fresh and used samples of 5% Zn/SiO2 and 10% Zn/SiO2 catalysts
Fig 8 Thermo gravimetric analysis (TGA) curve of fresh and used 10% Zn/SiO2 catalysts in Air atmosphere
Fig 9 Raman spectroscopy (a) and normalized surface carbon deposit (b) of used 10% Zn/SiO2 catalysts with different Zn loadings
Fig 10 NH3Temperature Programmed Desorption (NH3-TPD) (a) and normalized surface acidity (b) of Zn/SiO2 catalysts with different Zn loadings
Fig 11 Possible activity center and deactivation mechanism for the dehydorchlorination of TCE over Zn/SiO2 catalysts
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