Dehydrochlorination of 1, 1, 2-trichloroethane over SiO2-supported alkali and transition metal catalysts: Tunable selectivity controlled by the acid - base properties of the catalysts

Dehydrochlorination of 1, 1, 2-trichloroethane was performed on SiO2 supported alkali metal (Na. K, Cs) and transition metal (Mn, Ni, Zn) catalysts. The surface basicity or acidity of the catalyst exerted great influence on catalytic behaviors. The catalysts with higher amount of base or acid sites resulted in higher activity due to more adsorption sites for reactant. The basic catalysts (Cs/SiO2 and K/SiO2) tended to form vinylidene chloride with a selectivity up to 80 %; the neutral catalysts (Na/SiO2 and SiO2) tended to form 1, 2-dichloroethene with a selectivity up to about 80 %; the acidic catalysts (Zn/SiO2, Mn/SiO2 and Ni/SiO2) tended to form 1, 2-dichloroethene with a selectivity up to 96 %. Proposed reaction mechanisms included an E1cb mechanism with a carbanion intermediate on the basic catalysts, an E2 concerted mechanism on the neutral catalysts, and an E1 mechanism with a carbonium intermediate on the acidic catalysts.