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 Brönsted acid (B) sites were detected on each of the samples. NH3 was found to bind to species formed from ammonia on the L and B sites (sites Ll and Lb) 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, Lb, and Ll. 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.