Physicochemical and catalytic characterization of non-hydrothermally synthesized Mg-, Ni- and Mg-Ni-saponite-like materials

Saponite-like materials with Mg2+ or Ni2+ ions and their mixt. in the octahedral sheet were non-hydrothermally synthesized. Their protonic forms were prepd. through deammoniation or by treatment with HCl. The products were characterized by phys. methods, gas-phase adsorption of amines and the catalytic transformation of 2-propanol and cumene via pulse and flow methods. The materials have a house-of-card' texture composed of platelets with small lateral dimensions and exhibit a high surface area and pore vol. Subsequent deammoniation resulted in the formation of non-framework Ni2+ and possibly Mg2+ ions. Mg-saponite, prepd. in this way, shows predominantly non-framework species formed by tetrahedrally coordinated Al3+ ions whereas its acid-treated counterpart contains Al3+ in both framework and non-framework positions.Deammoniated Ni-saponite exhibits a peculiar catalytic behavior, which manifests itself in the fact that the activity in the 2-propanol decompn. in a pulse expt. is low while under flow conditions it becomes the most active. This is ascribed to generation during the reaction of new acidic centers due to the dissociative adsorption of produced water on site pairs formed by coordinatively unsatd. non-framework Ni2+ and framework oxygen ions. Cumene conversion tests confirm this explanation. The high activity and stability of acid-treated Mg-saponite in cumene dealkylation underlines its potential use for high-temp. acid-catalyzed reactions. The Bronsted acidity of the saponite-like materials is related to their layer charge, cation exchange capacity and diminished with increasing Ni content, whereas the Lewis acidity increased. Both the gas-phase amine chemisorption and catalytic tests provide the same order of protonic acidity: Mg > MgNi > Ni. The origin of the acidic sites from deammoniation or HCl treatment is discussed. [on SciFinder (R)]