Comparative study on catalytic hydrodehalogenation of halogenated aromatic compounds over Pd/C and Raney Ni catalysts.

Xuanxuan Ma,Guodong Gu,Sujing Liu,Ying Liu,Chuanhai Xia

doi:10.1038/srep25068

Abstract

Catalytic hydrodehalogenation (HDH) has proved to be an efficient approach to dispose halogenated aromatic compounds (HACs). Liquid-phase HDH of single and mixed halobenzenes/4-halophenols with H2 over 5% Pd/C and Raney Ni catalyst are investigated and compared. For liquid-phase HDH of single HACs, hydrogenolytic scission reactivity of C-X bonds decreases in order of C-Br > C-Cl > C-I > C-F over Pd/C catalyst, and in order of C-I > C-Br > C-Cl > C-F over Raney Ni catalyst. To clarify the reason why hydrogenolytic scission reactivity of C-X bonds over Pd/C and Raney Ni catalysts exhibits different trends, liquid-phase HDH of mixed HACs over Pd/C and Raney Ni catalysts were studied, and catalysts are characterized by SEM, EDX, and XRD techniques. It was found that the high adsorption of iodoarenes on Pd/C catalyst caused the HDH reactivity of iodoarenes to be lower than that of chloroarenes and bromoarenes in the HDH of single HACs. Moreover, the adsorption of in situ produced iodine ion (I−) to catalyst surface would result in the decline of catalytic activity, which might be the main reason why the HDH reactivity of HACs in the presence of NaI is rather low.

Highlights

Halogenated aromatic compounds (HACs) are important and versatile molecules with many applications in synthetic organic chemistry and industrial chemical processes[1]
Faucher et al found that the reactivity of HACs over Pd/C catalyst decreased in order of CB > BB > IB in liquid phase system, exactly to the true reactivity order of C-X bond[34]
For liquid-phase HDH of single HACs, hydrogenolytic scission reactivity of C-X bonds decreases in order of C-Br > C-Cl > C-I > C-F over Pd/C catalyst, and in order of C-I > C-Br > C-Cl > C-F over Raney Ni catalyst

Summary

Introduction

Halogenated aromatic compounds (HACs) are important and versatile molecules with many applications in synthetic organic chemistry and industrial chemical processes[1]. Several methods have been developed for the remediation of HACs, including incineration[6], microbial degradation[7], chemical oxidation[8], photochemical degradation[9], ultrasonic irradiation[10], electrolysis[11], and catalytic hydrodehalogenation (HDH)[12,13,14,15]. We compared hydrogenolytic scission reactivity of C-X bonds in liquid-phase HDH of single HACs over Pd/C and Raney Ni catalyst with halobenzenes and 4-halophenols as the representative. In order to verify the trend of hydrogenolytic scission reactivity of C-X bonds, liquid-phase HDH of mixed HACs over Pd/C and Raney Ni catalyst were further carried out. The effect of halide ion on catalytic HDH of HACs over Pd/C and Raney Ni catalyst were investigated

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