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

•High surface basicity or acidity promoted adsorption of reactant and thus activity.•Stronger basicity of catalyst favored higher selectivity to vinylidene chloride.•Medium Lewis acidity favored the formation of cis-1, 2-dichloroethene.•Acid-base properties of the catalysts led to E1cb, E1 and E2 mechanisms.