ACID-MODIFIED&NICKEL EXCHANGED MORDENITE FOR GAS-PHASE HYDRODECHLORINATION OF TRICHLOROETHYLENE

Date

2023-6-12

Author

Akyıldız, Enes

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Contamination of groundwater due to halogenated hydrocarbons is a growing environmental issue because of their abundant utilization in industry and their toxic nature which brings serious concerns about human health. Trichloroethylene (TCE) is one of the frequently observed halogenated compounds in groundwater. Among different water treatment methods, catalytic hydrodechlorination (HDC) effectively removes chlorinated hydrocarbon. Catalytic treatment via HDC is an elimination-based method where the reaction occurs by interacting chlorinated hydrocarbons with hydrogen on a metal catalyst surface, resulting in hydrogen chloride (HCl) and chloride-free hydrocarbons. HDC can be applied on both aqueous and gas phases. The phase of the reaction brings different challenges such as the groundwater matrix effect and proposes different mechanisms and application areas. Numerous studies on different combinations of metals and supports for HDC demonstrate favorable catalytic performance, yet, challenges such as (i) catalyst inhibition due to the reaction product HCl which is irreversibly adsorbed on active sites and causing deactivation, in other words, chloride poisoning, (ii) formation of carbonaceous species on active sites. To adapt catalytic HDC as an elimination-based technique in the industry these challenges still need to be addressed and improved. Herein this study, the acidity effect of zeolite support material has been tested with dealuminated mordenite (MOR). Since the degree of dealumination directly affects the acidic properties of catalyst support, dealumination was carried out with 6 M and 13 M nitric acid (HNO3) concentrations, and one sample was left bare without dealumination. Si/Al ratios of HMOR, 6MHMOR, and 13MHMOR are 10, 58, and 101 respectively. Nickel loading to MOR samples was done via ion exchange. Physisorption and crystallographic analysis showed that 3 different acid catalysts remained stable in terms of textural and crystal properties upon harsh-dealumination. The elemental analysis also showed that the percentages of Nickel loadings were similar for all three catalysts. DRIFTS of adsorbed pyridine on dealuminated MORs have shown that number of strong acid sites decreased with respect to the increased degree of dealumination. The activity results of three catalysts showed that the optimized acidity of the catalyst support has a remarkable effect on HDC performance. In terms of percent conversion loss, Ni-6MHMOR presented the best performance with a low amount of carbon and Cl- deposition. Highest carbon formation and Cl- deposition was observed with bare Ni-6MHMOR catalyst during the TGA and TPH analysis.

Subject Keywords

Hydrodechlorination, Trichloroethylene, Nickel, Dealumination, Pyridine DRIFTS, Mordenite, Zeolite

URI

https://hdl.handle.net/11511/104494

Collections

Graduate School of Natural and Applied Sciences, Thesis