New methods for quantitative determination of Bronsted acid sites on solidacids: Applicability and limits for Al2O3-promoted SO42-/ZrO2 catalysts

Two quantitative methods, both based on H/D exchange, have been developed f or the Bronsted acid sites titration on solid acids. The agreement between the results obtained with the two methods on unpromoted sulfated zirconia ( SZ) is remarkable: 0.061 and 0.064 mmol of H/g of catalyst were respectivel y found with the first (anhydride method) and the second (isobutane method) method. Furthermore, the use of a small alkane as the probe molecule with the isobutane method gives us information about the capacity of the solid t o activate an alkane. Nevertheless, this last method is hard to apply to ve ry active catalysts such as 3% alumina-promoted sulfated zirconia (SZA3). I ndeed, it was not possible in this case to find optimal temperature conditi ons, low enough to minimize secondary reactions such as isomerization or cr acking and, at the same time, sufficiently high for an accurate quantitativ e H/D exchange measure. On the other hand, the anhydride method was always applicable to SZAn catalysts and the obtained results were very reproducibl e. (C) 2001 Academic Press.