Hydrogen exchange between sulfated zirconias and per deutero-benzene as characterization of the surface acidity - Study by DRIFT and H-1 MAS-NMR spectroscopies

The surface acidity of sulfated zirconia has been investigated by diffuse reflectance IR and H-1 MAS-NMR spectroscopies. Both techniques give evidence of the existence of two types of acid sites: a weak acid characterized by an infrared band at 3630 cm(-1) and an H-1 NMR resonance at 3.5 ppm relative to TMS, and a strong acid characterized by resonances at 3300 cm(-1) in infrared and 5.8 ppm in H-1 NMR. The interaction of deuterated benzene with these solids also shows two types of acid sites: the weaker sites give hydrogen bonding with benzene, evidenced by a shift of the resonance frequency in infrared spectrometry. The presence of strong acid sites able to exchange protons with deuterated benzene has been ascertained by FTIR and NMR investigation of the adsorbed phase and by mass spectrometric analysis of the effluents. The catalytic properties in isomerization of n-hexane are correlated with the presence of these strong acid sites, the formation of which depends on the type of preparation of the catalyst. (C) 1997 Academic Press.