Study On Catalytic Hydrodechlorination Of Chlorinated Aromatic Hydrocarbons Over Supported Pd, Ru, Rh Catalysts

Chlorinated aromatic hydrocarbon have been receiving increasing concern for which had a great threat to human health and could cause serious environmental pollution due to their high toxity and low degradability. The catalytic hydrodechlorination is considered to be the most promising method for eliminating of chlorinated aromatic hydrocarbon because of it is simple, safe and efficient. Many a researchers paid much attention to the hydrodechlorination in both gas-phase and liquid-phase with various catalysts.In this work, by means of studying catalytic hydrodechlorination of chlorinated aromatic hydrocarbon were developed in liquid phase under mild conditions. Using precipitation method make a series of catalysts with different contents, different supports, different active component, and were characterized by energy Dispersive X-ray Fluorescence (EDXRF), Brunauer-Emmett-Teller (BET) specific surface area, X-ray diffraction (XRD), CO-chemisorption and H2-temperature programmed reduction (H2-TPR) analysis, to identify the specific surface area, morphology, particle shape, particle size, crystal structure and dispersion.3%Pd/C catalysts for hydrodechlorination of 1,2,4,5- tetrachlorobenzene, as expected, benzene is the major product, besides, a small amount of chlorobenzene, o-dichlorobenzene. Interestingly, the possible products such as m-DCB, cyclohexane, or chlorocyclohexane were not monitored,1,2,4-trichlorobenzene was an intermediate product. From Arrhenius equation, the overall apparent activation energy in the range 293-323 K was estimated to be 34.1 kJ/mol, showing a first order feature. Further study we investigated the catalytic activities of SiO2, γ-Al2O3, CeO2, carbon, ZrO2 and SBA-15 supported Pd catalysts for HDC of TeCB and found that different supports loaded Pd catalysts exhibited different catalytic HDC activities. Without consideration of supports’properties, carbon was the best supports.The effects of the different active components of catalysts for hydrodechlorination, with respect to the nature of the metal decreases in the following order:Pd>Ru>Rh, and the substitution position of hydrodechlorination in the following order:meta-> para-> ortho-. And hydrodechlorination actions of chlorinated aromatic hydrocarbon are consistent with electrophilic reaction mechanism, when a compound structure containing electron donating groups with high hydrodechlorination efficiency.