Catalytic Dechlorination Of Trichloroethylene By Mesoporous Alumina-Supported Ni-Fe_xO_y

Nickel-based catalysts exhibit good activity for hydrogenation. Nanoscale bimetallic nickel-iron particles have been studied to degrade chlorinated hydrocarbons in water. However, more long lasting catalysts are needed. In this research, nickel-iron oxides catalyst supported on mesoporous alumina is prepared to dechlorinate trichloroethylene.Mesoporous alumina was prepared by sol-gel method. And Ni-Fe hydrotalcite-like precursor on the mesoporous alumina was prepared by consecutive impregnation and co-precipitation. Subsequently the precursor was reduced by hydrogen gas to form Ni-FexOy/mesoporous alumina, which was characterized by XRD, N2adsorption-desorption measurement, SEM-EDS, TEM and XPS. The dechlorination mechanism for trichloroethylene was deduced. And the effects of molar ratio of Ni to Fe, reduction temperature, etc, on dechlorination efficiency of trichloroethylene were evaluated. Trichloroethylene was spiked8times to assess the longevity of Ni-FexOy/mesoporous alumina. The results are as follows:(1) The BET specific surface area of mesoporous alumina is350m2/g, and its pore size is centered at5.48nm. Crystalline nickel and FeNi3were detected in the Ni-FexOy. The unsupported Ni-FexOy particles aggregated together, with sizes in the range of50-100nm. In comparison, the Ni-FexOy on mesoporous alumina, which is produced at400℃, was much more dispersed with a uniform size of about20nm. After reaction with trichloroethylene, crystalline nickel in the Ni-FexOy/mesoporous alumina was oxidized to Ni(OH)2or NiO, while FexOy was partly oxidized to FeOOH or Fe2O3.(2) Mesoporous alumina and FexOy/mesoporous alumina showed adsorption ability toward trichloroethylene, with degradation ratio of55.9%and58.5%at60h respectively. The degradation ratio of trichloroethylene was95.9%, whereas the yield of two-carbon hydrocarbons was only1.3%over Ni-FexOy. The degradation ratio of trichloroethylene and yield of two-carbon hydrocarbons were78.9%and3.9%respectively over Ni/mesoporous alumina.(3) The dechlorination occurred mainly via elimination-hydrogenation mechanism over the Ni-FexOy/mesoporous alumina. And the products are acetylene, ethylene and ethane, with ethylene predominating.(4) The Ni-FexOy/mesoporous alumina with Ni/Fe/Al molar ratio of0.75/0.25/1and reduced at400℃exhibited the best dechlorination activity. The degradation ratio of trichloroethylene was99.3%in60h, while the yield of two-carbon hydrocarbons was12.3%, with ethylene selectivity of98.3%.(5) The degradation of trichloroethylene were1.89μmol,2.33μmol,2.19μmol and2.01μmol respectively after four runs of spiking over Ni-FexOy/mesoporous alumina, with the corresponding yields of two-carbon hydrocarbons of0.25μmol,0.27μmol,0.24μmol and0.23μmol. Initial amount of trichloroethylene increased after each spiking.