AN NMR-STUDY OF ACID SITES ON SULFATED-ZIRCONIA CATALYSTS USING TRIMETHYLPHOSPHINE AS A PROBE

Concentrations of Bronsted and Lewis acid sites on sulfated-zirconia c atalysts were determined using the P-31 MAS NMR spectra of adsorbed tr imethylphospine. A sample that had been calcined and exposed to air fo r a long period exhibited only Bronsted acidity; however, treatment of the sample at progressively higher temperatures resulted in the devel opment of at least three types of Lewis acidity, along with a decrease in the concentration of Bronsted acid sites. In a related study the a ctivity of these catalysts for the alkylation of isobutane with 2-bute ne was determined. The aged catalyst was inactive, but activation of t he material at 100-degrees-C resulted in the most active catalyst. The rmal treatment at higher temperatures resulted in a loss in activity w hich paralleled the decrease in the Bronsted acid sites. These results are consistent with a model in which strong Bronsted acidity is a res ult of the interaction between bisulfate groups and adjacent Lewis aci d sites.