title: Reductive dechlorination of 1,2,4-trichlorobenzene with palladized nanoscale Fe(zero-valent) particles supported on chitosan and silica.
abstract: In this study, nanoscale Pd-Fe particles, with diameters less than 100 nm, were synthesized and dispersed over the chitosan and silica supports. Three different Pd-Fe particles were synthesized, namely 0.1% Pd-Fe, 0.5% Pd-Fe and 1.0% Pd-Fe. SEM images confirmed that the Pd-Fe particles were dispersed over the surface of the supports while SEM-EDX confirmed evenly distribution of Pd over Fe(zero-valent). alpha-Fe(zero-valent) crystallites were identified by means of XRD and observed in TEM. Reductive dechlorinations of 1,2,4-trichlorobenzene (1,2,4-TCB) with the nanoscale Pd-Fe/chitosan and Pd-Fe/silica were carried out in the batch experiment system. Disappearance of the parent species and formation of the reaction intermediates and end product were monitored at discrete times. The results show that the nano-scale Pd-Fe particles were able to completely dechlorinate the chlorinated benzenes within a very short timescale. Complete dechlorinations of 1,2,4-TCB to benzene were achieved within 60 min with the 1.0% Pd-Fe/chitosan and within 100 min with the 1.0% Pd-Fe/silica. Reaction rates were observed to increase with increasing Pd content of the Pd-Fe/support. The reactions apparently followed pseudo-first-order kinetics with respect to the 1,2,4-TCB transformation. A kinetic model is constructed to fit the experimental results for the reactions, enabling identification of the major and minor dechlorination pathways of 1,2,4-TCB. The model suggests that the 1,2,4-TCB transformation mainly followed the primary pathway of direct reductive dechlorination to benzene and secondary pathway of sequential hydrogenolysis to 1,2-dichlorobenzene (1,2-DCB) and then chlorobenzene (CB) or benzene.
authors.affiliation: Environmental Engineering Research Centre, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: Bao-Wei
authors.initials: BW
authors.lastname: Zhu
authors.forename: Teik-Thye
authors.initials: TT
authors.lastname: Lim
authors.forename: Jing
authors.initials: J
authors.lastname: Feng
mesh_terms: D048271:Chitosan / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry; D002722:Chlorobenzenes / Q000737:chemistry*; D004785:Environmental Pollutants / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010165:Palladium / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D002722:Chlorobenzenes; D004785:Environmental Pollutants; C009947:1,2,4-trichlorobenzene; D002713:Chlorine; D010165:Palladium; D012822:Silicon Dioxide; D048271:Chitosan; D007501:Iron