Gas phase benzene hydrogenation on a nickel-silica catalyst II. Gravimetric experiments of benzene, cyclohexene, and cyclohexane adsorption and benzene hydrogenation

Abstract Studies of benzene adsorption on a nickel-silica catalyst have suggested the existence of three forms of chemisorption, in addition to physical adsorption. The chemisorbed forms cover only a part of the surface and are, respectively: (a) a reactive form, active in normal benzene hydrogenation, and discernible up to 110 °C, (b) a form of low reactivity, not contributing to normal benzene hydrogenation, and removable by several hours hydrogen flow at the temperature of adsorption, and (c) a dissociatively adsorbed form, occurring above 120 °C, in the absence of hydrogen. This last form acted as a poison for the hydrogenation reaction and was only removable by hydrogen at 400 °C or above. Cyclohexane adsorbed in hydrogen atmosphere (30–200 °C) proved to be easily removable by hydrogen.