Acidity and cracking activity on MgHY zeolite

Solid acidity of Mg cation exchanged HY zeolite was characterized by means of IRMS-TPD experiments of ammonia. Enthalpy (Delta H) of ammonia desorption on the Bronsted acid site was kept nearly a constant 111 kJ mol(-1) with introducing Mg, while a strong Lewis acid site with 140-160 kJ mol(-1) of Delta H was generated. Desorption energies of NH3 on Mg2+ cation located in site I' and Mg-OH+ in site III, which were calculated by a density functional theory, were in agreement with the measured values. Catalytic activity for octane cracking was significantly increased by the introduction of Mg, and the activity was higher on the MgHY than on the Ca- and Ba-HY at more than 40% of the exchange degree. As a prominent character of the catalysis, hydrogen was formed in the cracking of octane on the MgHY. Discussion was made on the acidity and cracking activity of the MgHY, which was distinctively different from on Ca- and Ba-HY. (C) 2011 Elsevier Inc. All rights reserved.