On The Gas-Phase Catalytic Hydrodechlorination Of Chlorobenzene And1,2-Dichloroethane Over Supported Catalysts

Gas-phase catalytic hydrodechlorination (HDC) was considered as a highly effective, cost-effective technique for the elimination of chlorinated organic pollutants. Supported catalysts were commonly used in HDC. The structure properties of support, the metal type and metal dispersion, and preparation method would impact the activity and stability of the catalyst. In this thesis, the HDC of chlorobenzene and dichloroethane was systematically studied on different catalysts. The relationship between the structural properties and the catalytic performance of the catalyst was elucidated.The thesis included three reaction systems:(1) chlorobenzene hydrodechlorination over Pd supported on TiO2nanotube (Pd/TNT),(2) dichloroethane in acetone over Cu supported on γ-Al2O3(Cu/Al2O3), and (3) dichloroethane in acetone over Cu supported on TiO2(Cu/TiO2). The catalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), acid-base titration, CO chemosorption, H2-temperature programmed reduction (TPR), elements analysis (ICP) and N2adsorption-desorption. The conclusion was summarized as follows,The HDC of chlorobenzene over Pd/TNT synthesized via the traditional impregnation and deposition-precipitation method was investigated. TiO2nanotube was calcined at250,400,550℃, respectively. As the calcination temperature increased, the structure of TNT collapsed gradually, the specific surface area and the content of the surface hydroxyl group decreased, while the crystallinity of the catalyst increased. The highest Pd dispersion was identified on Pd/TNT when TiO2nanotube was calcinated at400℃. Accordingly, Pd/TNT-400synthesized via the deposition-precipitation method exhibited the best catalytic performance with a chlorobenzene conversion rate of92%. The activity of Pd/TNT mainly depended on the metal dispersion, morphology and crystallinity of the catalyst. Additionally, the presence of Pdn+resulting from the strong metal-interaction between metal and support could markedly enhance catalytic activity. Furthermore, surface hydroxyl from catalyst support could transfer chlorine from metal to support, effectively suppressing catalyst poisoning.The influence of trace1,2-dichloroethance on the catalytic hydrogenation of acetone on Cu/Al2O3was investigated. The catalyst was prepared using the impregnation and deposition-precipitation methods. The Cu/Al2O3catalyst exhibited very stable catalytic activity for the hydrogenation of acetone to isopropanol in the absence of1,2-dichloroethance. At Cu particle size below5nm, the catalytic activity of the catalyst increased with Cu particle size. However, the presence of trace1,2-dichloroethance suppressed the catalytic activity, and some polymers were identified as the products along with isopropanol. The doping of Cu/Al2O3with other metals, e.g. Pd, Ni, and Zn, led to decreased Cu particle size, giving rise to decreased catalytic activity. Additionally, Zn doping resulted in fast catalyst deactivation. Pd doping did not influence the deactivation rate, while Ni doping suppressed chlorine poisoning and metal sintering.The Pd-Cu/TiO2catalysts were prepared using the photodeposition, replacement reaction, and precipitation-deposition methods, and the influence of trace1,2-dichloroethane on the catalytic hydrogenation of acetone on these catalysts were investigated. It was observed that the reaction mechanism on Cu/TiO2was apparently different from that on Cu/Al2O3. The catalyst with smaller Cu particles exhibited a higher catalytic activity. Additionally, the catalysts prepared using three different methods differed in the structural properties as well as the catalytic activities. The initial catalytic activity of the catalyst prepared by the replacement method was about5%. In contrast, the catalysts prepared by the photodeposition and precipitation-deposition methods exhibited enhanced catalytic activities. Particularly, due to a high Cu exposure the catalyst obtained by the photodeposition method had a higher Cu dispersion, giving rise to the optimized catalytic activity and stability.