Study On Hydrodechlorination Of Chlorinated Phenol With Pd-Sn Catalyst

With the rapid development of the chemical industry,the problem of groundwater pollution with chlorophenols has received increasing attention.Chlorophenols are difficult to degrade when they enter the groundwater,which brings great harm to human health.At present,the catalytic reduction method is widely used in the treatment of chlorophenol compounds because of its advantages of economy,high efficiency,and no pollution.In this paper,we prepared a series of supported Pd-Sn/AC bimetallic catalysts with Pd loading of 1% in the catalysts with different Sn/Pd mole ratio using equal volume impregnation method and unsupported Pd-Sn bimetallic catalysts with microemulsion method with different Sn/Pd mole ratio and studied the catalytic performance for hydrodechlorination of chlorophenols in the water.We characterized the crystal structure,surface morphology,particle shape,particle size and lattice parameters of Pd and Sn metal particles by scanning electron microscopy-X-ray dispersive energy spectroscopy(SEMEDX),high resolution transmission electron microscopy(HR-TEM),temperature programmed reduction(TPR),X-ray electron energy spectroscopy(XPS),and H2 pulsed chemisorption methods.The reaction was carried out in a glass reactor using H2 as a reducing agent.The reaction was carried out by adding an aqueous solution of pchlorophenol and catalyst in a glass apparatus,and the resulting product was analyzed by gas chromatography.The influence of the molar ratio of tin to palladium on the activity and selectivity of the catalyst was investigated.The best active palladium-tin catalyst was selected from the above experiments.The kinetic experiments were performed on the three isomers of chlorophenol(p-chlorophenol,m-chlorophenol and o-chlorophenol)using a palladium tin catalyst and a palladium catalyst,respectively.The effect of the catalyst on the three isomers at different temperatures was examined.The experimental results shows that the particles of Pd and Sn in the supported Pd-Sn catalysts are uniformly distributed on the support.In the supported palladium-tin catalysts,the particle size of Pd metal is in between 2 nm and 5 nm.With the increase of the Sn/Pd molar ratio in the catalysts,the amount of Sn-Pd alloy produced in the catalyst gradually increased.The activity of the catalyst increased first and then decreased with the increasing of Sn/Pd molar ratio.This is because the addition of a small amount of Sn canincrease the dispersion and specific surface area of Pd.When the molar ratio of Sn/Pd is0.3/1 the catalyst has the best catalytic activity.At that case,the dispersion and specific surface area of Pd in the catalyst reached the largest,45.0% and 94.3m2g-1,respectively.When the molar ratio of tin to palladium was higher than 0.3/1,the catalytic activity of the catalyst decreased due to the formation of a large amount of tin-palladium alloy in the catalyst.In the unsupported Pd-Sn bimetallic catalyst,the particle size of the catalyst did not change much,and it was also between 2 nm and 5 nm.With the increase of the content of tin,the catalytic activity of this series of catalysts gradually decreases,but the overall catalytic effect is significantly lower than that of the supported palladium tin catalyst.This is mainly due to the fact that in the absence of support,the amount of alloy formed in the unsupported catalyst is significantly higher than that of the supported catalyst in the same molar ratio,and the formation of the alloy is not conducive to the improvement of the catalytic activity of the catalyst.In the kinetic experiments,the activation energy of hydrodechlorination reaction of the three isomers was in the order of o-chlorophenol>m-chlorophenol>p-chlorophenol for Pd/AC catalyst;the activation energy of hydrodechlorination reaction of the three isomers was o-chlorophenol>p-chlorophenol>m-chlorophenol for Pd-Sn/AC bimetallic catalyst.The rate of hydrodechlorination of the three isomers can be described using firstorder kinetics,and the rate of dechlorination increased as the reaction temperature increasing.