An NH3-TPD and -FR study on the acidity of sulfated zirconia

Temperature-programmed desorption (TPD) and frequency response (FR) methods were used to study the dynamics of ammonia sorption over sulfated zirconia (SZ). The results were interpreted in comparison with results obtained for zirconia (Z) sulfated zirconia-titania (SZT) and zeolite H-ZSM-5 (HZ). Strong Lewis (L) and Bronsted acid (B) sites were detected on each of the samples. NH3 was found ro bind to species formed from ammonia on the L and B sites (sites L-b and L-t) by H-bonds. The H-bound ammonia was released at lower temperatures than that directly bound to the B and L sites. FR resonance signals were ascribed to sorption processes over sites B, L-b, and L-t. The L sites were fully covered by NH3 up to the highest temperature of the FR measurement, therefore, these sites could not be detected. For SZ and SZT, the FR intensity was found independent of the temperature suggesting that these samples contain energetically heterogeneous sorption sites. (C) 2001 Elsevier Science B.V. All rights reserved.