Sulfated ZrO2 Research Articles

Relationship between the Scaling of the Acid Strength of Lewis Sites by EPR and NMR Probes

While numerous techniques have been successful for scaling the acid strength of Brønsted sites, the situation is not satisfactory at all, for the Lewis acid sites. This is most unfortunate, since Lewis sites are present in most acid catalysts. This contribution aims to show that the simultaneous use of EPR and NMR probes suggests solutions to the problem of scaling the acid strength of Lewis sites. As shown previously, the hyperfine splitting of the EPR spectrum of the aniline radical cation or of the O−2 superoxide ion is a measurement of the strength of the electron acceptor site. Other researchers have suggested the shielding of the 31P nucleus and the shift of its resonance lines in chemisorbed trimethylphosphine (TMP) as a measurement of the Lewis acid strength. The comparison of the scaling obtained on a set of superacids, namely, and in the decreasing order of acidity, the sulfated derivatives of ZrO2, HfO2, Al2O3 and TiO2, by either the EPR or the NMR probes gives interesting information. While very strong Lewis acid centers in sulfated ZrO2 and HfO2 are revealed by 31P downfield shifted resonance lines, no such lines are observed in sulfated Al2O3 or TiO2 or zeolites (such as dealuminated mordenite) which contains strong Lewis acid centers. In the latter samples, the most downfleld shifted line corresponds to that generally assigned to TMPH+. Measurement of 31P relaxation rates suggests that TMP has a more restricted mobility on strong than on weak Lewis sites. They also show that the origin of the relaxation in TMPH+ is ambiguous: either the mobility of TMPH+ is very restricted and/or the extraproton is not as close to the phosphorus as anticipated.

Catalytic Disproportionation of Alkylsilanes over Sulfated ZrO2

Abstract Gas phase heterogeneous catalytic conversions of diethylsilane(E2), triethylsilane(E3) and diethyldimethylsilane(E2M2) were examined at 373–573 K in a closed recirculation reactor by using a sulfated ZrCO2(SO3/ZrO2) catalyst. The catalyst exhibited high disproportionation activity even at 373 K.

A highly active solid superacid catalyst for n-butane isomerization: a sulfated oxide containing iron, manganese and zirconium

A prorous sulfated metal oxide containing Fe, Mn and Zr is described; it is the most active nonhalide superacid catalyst yet reported, catalysing the isomerization of n-butane at 301 K and being about three orders of magnitude more active than sulfated ZrO2.

Acidity of zirconium oxide and sulfated ZrO 2 samples

Lewis acidities of pure zirconium oxide and of two sulfated samples containing 200 or 280 μmol g −1 of sulfate, activated at 720K, have been compared by FT-IR using probe molecules such as CO, CO 2 and pyridine. The sulfated samples show an increase of the strength of some Lewis acid sites. However, their number does not seem to be affected. CH 3SH adsorption is very sensitive to the presence of sulfate : on pure ZrO 2, it dissociates while on sulfated samples it is mainly coordinated. It is therefore deduced that sulfate formation involves the basic oxygen atoms which also facilitate the dissociation of CH 3SH. The increase of the Lewis acidity observed, in the activation conditions used, is not sufficient to explain alone the superacidic properties of sulfated zirconia.