Alcohol dehydration reactions over tungstated zirconia catalysts

The behavior of tungstated zirconia (WZ) toward dehydration of 1-propanol, 2-propanol, and tert.-butanol was compared with that of H-mordenite. For 1- and 2-propanol, the desorption temperatures of olefinic products formed over the WZ catalyst were found to be very close to those observed in H-mordenite; however, the zeolite catalyst had a much larger tendency to retain (or to readsorb) olefins in the pores in the form of oligomerization products, as evidenced by the detection of the m/e = 65 signal (cyclopentadienyl cation) during the temperature-programmed reaction of 2-propanol. The Brønsted acid sites of the zeolite underwent rapid H⁺/D⁺ exchange when 2-propanol deuterated in its hydroxyl group was used. This allowed the olefinic products to incorporate deuterium during reaction. On the other hand, the WZ catalyst did not effect the H⁺/D⁺ exchange of propene formed from CH₃-HCOD-CH₃, presumably because olefin readsorption onto hydrated W⁶⁺ sites does not take place. The structure of the WZ catalyst was monitored by EXAFS and XRD.