NMR study of tungstated zirconia catalyst: characterizing the surface of tungstated zirconia and the influence of reduction treatment

In this NMR study, reduction treatment formed and increased Bronsted acid sites on tungstated zirconia (WZ); in contrast, Lewis acid sites was decreased. The upfield shift of pyridine bound to Bronsted acid sites (from -173 to -181 ppm) in reduced and evacuated WZ was ascribed to the increased interaction between pyridine and the H+ of the Bronsted acid sites, indicating that reduction treatment not only increased the number of Bronsted acid sites but also enhanced their strength. However, this upfield shift was not observed in the 31P NMR spectra of trimethylphosphine (TMP). Bronsted acid strength is not high when compared with that of zeolite. (C) 2002 Published by Elsevier Science B.V.