Sulfated zirconia promoted with alumina

Traditionally, solid acidic catalysts are applied in industry for the oligomerization of butenes and are still studied. MTS-type aluminosilicates,522 a NiCsNaY zeolite,523 and a silica-alumina containing 13% alumina524 proved to be active and selective catalysts. Moreover, deactivation rates of these catalysts are also favorable. Sulfated zirconia promoted with Fe and Mn was active and selective to yield primarily dimethylbutene isomers under supercritical conditions.525 A small amount of water improved productivity and decreased deactivation. A study showed that the blending octane number of Cg hydrocarbons is directly linked to the number of allylic hydrogens in the molecules.526... 

Sommer and coworkers have made important observations with respect to the activation of alkanes over sulfated zirconia, a new type of solid superacid. Whereas isotope exchange of small alkanes occurs with the involvement of the corresponding pentacoordinate ions, a classical carbenium ion-type mechanism was found to be operative for larger homologs (propane, isobutane). The exception is the isomerization of n-butane over sulfated zirconia promoted by Pt and alumina, where the initiation step for isomerization was suggested to be the protolysis of the C-H bond. ... 

Furuta et al. tested a series of strong solid acids (alumina promoted sulfated zirconia, alumina promoted tungstated zirconia and sulfated tin oxide) for the transesterification of soybean oil with methanol at 200-300°C. Reaction yields over 90% were obtained for the alumina promoted tungstated zirconia at reaction times of 20 h using a flow reactor T = 250°C). The activity of the same catalyst was maintained for up to 100 h. 

In the sol-gel field, this technique has been used only recently in a few investigations. The change in the work function of alumina and alumina-zirconia xerogels, for example, was determined during the impregnation with a sulfate which promotes a charge transfer from Zr and A1 to oxygen species, due to an increase of Lewis acidity (Younes, 2003). 

Acidic or basic promoters can affect the activity of Pt and Pd supported on alumina or zirconia. Basic promoters (e.g. Na) improve CO and propene oxidation while they inhibit NO oxidation. By contrast, acidic promoters (e.g. sulfates) show the greatest effect in propane oxidahon. Carbon monoxide and propene are too shongly adsorbed (with respect to O2) the effect of basic promoters would be to weaken their adsorphon on the metals and thereby to reinforce that of oxygen. The reverse is true for acidic promoters they strengthen the adsorption of propane, too weakly adsorbed on Pt and Pd (see Section 1.2.5). The same result can be observed if sulfates are replaced by SO2 directly injected with the propane/air mixture. The... 

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