Studies On Liquid-phase Dechlorination Of Chlorophenols Over Synthesized And Modified Pdcob Amorphous Catalysts

Since the emission of chlorophenols to the environment caused serious pollutions, liquid-phase catalytic hydrodechlorination (HDC), has received the researchers’ attention owing to its various advantages in disposing the chlorinated organic compounds. The bimetallic catalysts have gotten more and more applications because they are able to react with water to produce hydrogen source. In this dissertation, taking Pd modified CoB amorphous alloy catalysts (PdCoB) and chlorophenols (4-chlorophenol,2,4-dichlorophenol,2,4,6-trichlorophenol) as the case research objects and probe molecules respectively, water-phase hydrodechlorination performances and kinetics were investigated.PdCoB-PR catalyst prepared by precipitation-reduction shows significantly higher activity for the dechlorination of4-chlorophenol than PdCoB catalysts prepared by co-reduction and reduction-replacement. The great difference in activity is caused by the structure factors, such as specific surface area, dispersion, particle size and electronic factors, such as electron-deficient Pd centers.The optimized preparation conditions of PdCoB-PR catalyst is:COSO4as cobalt precursor,273K as preparation temperature, Pd/Co=0.0005wt and molB/molM=7as dosage ratio of PdCl2and NaBH4,1h as reduction time. Then, the Kobs of80mg/L4-chlorophenol with1.25g/L PdCoB-PR reached0.433min-1. On the other hand, dechlorination activity of4-CP with PdCoB-PR remained as pH ranging from2.5to11and deactivation was observed only in extremely acidic and alkaline solutions.Compared with PdFe catalysts reported in other literatures, PdCoB-PR showed much higher activity and selectivity for the dechlorination of chlorophenols. The activity dropped down to77%,50%and38%in Runs2,3and4, respectively, when PdCoB-PR participated in dechlorination process continuously. The cover of Co(OH)2precipitates with flocculent shape on nano-particles may account for the deactivation. The dechlorination mechanism of CPs in PdCoB-PR system is the hydro-dechlorination caused by atomic hydrogen (H*) which is decomposition of H2gas by Pd.